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  • Oxford University Press  (209,586)
  • American Geophysical Union  (100,964)
  • 2020-2022  (29,824)
  • 2015-2019  (119,928)
  • 2010-2014  (110,527)
  • 1990-1994  (48,025)
  • 1945-1949  (2,246)
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  • 1
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    Great Policy Successes (2019)
    Oxford University Press
    Details
    Publication Date: 2024-03-23
    Description: "With so much media and political criticism of their shortcomings and failures, it is easy to overlook the fact that many governments work pretty well much of the time. Great Policy Successes turns the spotlight on instances of public policy that are remarkably successful. It develops a framework for identifying and assessing policy successes, paying attention not just to their programmatic outcomes but also to the quality of the processes by which policies are designed and delivered, the level of support and legitimacy they attain, and the extent to which successful performance endures over time. The bulk of the book is then devoted to 15 detailed case studies of striking policy successes from around the world, including Singapore's public health system, Copenhagen and Melbourne's rise from stilted backwaters to the highly liveable and dynamic urban centres they are today, Brazil's Bolsa Familia poverty relief scheme, the US's GI Bill, and Germany's breakthrough labour market reforms of the 2000s. Each case is set in context, its main actors are introduced, key events and decisions are described, the assessment framework is applied to gauge the nature and level of its success, key contributing factors to success are identified, and potential lessons and future challenges are identified. Purposefully avoiding the kind of heavy theorizing that characterizes many accounts of public policy processes, each case is written in an accessible and narrative style ideally suited for classroom use in conjunction with mainstream textbooks on public policy design, implementation, and evaluation.
    Keywords: public policy ; policy evaluation ; government ; governance ; social policy ; health policy ; economic policy ; thema EDItEUR::J Society and Social Sciences::JP Politics and government
    Language: English
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  • 2
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    Millimeter wave spectroscopic measurements over the South Pole: 5. Morphology and evolution of HNO3vertical distribution, 1993 versus 1995 (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: We compare differences and similarities in the annual stratospheric HNO3 cycle derived from ground‐based measurements at the South Pole during 1993 and 1995, after correcting an error in earlier published profile retrievals for 1993 which led to under estimation of mixing ratios. The data series presented here provide profiling over the range ∼16–48 km, and cover the fall‐winter‐spring cycle in the behavior of HNO3 in the extreme Antarctic with a large degree of temporal overlap. With the exception of one gap of 20 days, the combined data sets cover a full annual cycle. The record shows an increase in HNO3 above 30 km occurring about 20 days before sunset, which appears to be the result of higher altitude heterogeneous conversion of NOx as photolysis diminishes. Both years show a strong increase in HNO3 beginning about polar sunset, in a layer peaking at about 25 km, as additional NOx is heterogeneously converted to nitric acid. When temperatures drop to the polar stratospheric cloud (PSC) formation range near the end of May, gas phase HNO3 is rapidly reduced in the lower stratosphere, although at least 2–3 weeks of temperatures ≤192 K appear to be required to complete most of the gas‐phase removal at the upper end of the depletion range (22–25 km). Despite a significant difference in residual sulfate loading from the explosion of Mount Pinatubo, there appears to be little gross difference in the timing and effects of PSC formation in removing gas phase HNO3 in these 2 years, though removal may be more rapid in 1995. Incorporation of gas phase HNO3 into PSCs appears to be nearly complete up to ∼25 km by midwinter. We also see a repeat of the formation of gas phase HNO3 in the middle stratosphere in early midwinter of 1995 with about the same timing as in 1993, suggesting that this phenomenon is driven by a repetition of dynamical transport and appropriate temperatures and pressures in the polar night, and not (as has been suggested) by ion‐based heterogeneous chemistry that requires triggering by large relativistic electron fluxes. High‐altitude HNO3 production peaks during a period of ∼20 days, but appears to persist for up to ∼40 days in the 40–45 km range, ceasing well before sunrise. This HNO3 descends rapidly throughout the production period, at a rate in good agreement with theoretically determined midwinter subsidence rates. As noted in earlier studies, later warming of this region above PSC evaporation temperatures does not cause reappearance of large amounts of HNO3, indicating that most PSCs gravitationally sink out of the stratosphere before early spring. We present evidence that smaller PSCs do evaporate to ∼1 to 3.5 ppbv of HNO3 in the lower stratosphere, however, working downward from ∼25 km as temperatures rise during the late winter. There is a delay of ∼15 days after sunrise before photolysis causes significant depletion in the altitude range below ∼30 km, where subsidence has carried virtually all higher‐altitude HNO3 by polar sunrise. Some continued subsidence and photolysis combine to keep mixing ratios less than ∼5 ppbv below 30 km until the final breakdown of the vortex in November brings larger amounts of HNO3 with air from lower latitudes.
    Description: Published
    Description: 17739-17750
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: ozone depletion ; HNO3 ; Antarctic stratosphere ; 01.01. Atmosphere
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 3
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    Evolution of temperature, O3, CO, and N2O profiles during the exceptional 2009 Arctic major stratospheric warming as observed by lidar and mm-wave spectroscopy at Thule (76.5°N, 68.8°W), Greenland. (2010)
    American Geophysical Union
    Details
    Publication Date: 2020-12-18
    Description: The 2009 Arctic sudden stratospheric warming (SSW) was the most intense event of this kind ever observed. Unique ground-based measurements of middle atmospheric profiles for temperature, O3, CO, and N2O obtained at Thule (76.5°N, 68.8°W), Greenland, in the period January – early March are used to show the evolution of the 2009 SSW in the region of its maximum intensity. The first sign of the SSW was detected at θ~2000 K on January 19, when a rapid decrease in CO mixing ratio took place. The first evidence of a temperature increase was observed at the same level on 22 January, the earliest date on which lidar measurements reached above ~50 km. The warming propagated from the upper to the lower stratosphere in 7 days and the record maximum temperature of 289 K was observed between 1300 and 1500 K potential temperature on 22 January. A strong vortex splitting was associated with the SSW. Stratospheric backward trajectories indicate that airmasses arriving to Thule during the warming peak underwent a rapid compression and an intense adiabatic warming of up to 50 K. The rapid advection of air from the extra-tropics was also occasionally observed to produce elevated values of N2O mixing ratio. Starting from mid-February the temperature profile and the N2O mixing ratio returned to the pre-warming values in the mid and upper stratosphere, indicating the reformation of the vortex at these levels. In late winter, vertical descent from starting altitudes of ~60 km is estimated from CO profiles to be 0.25±0.05 km/day.
    Description: Published
    Description: D24315
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 1.10. TTC - Telerilevamento
    Description: JCR Journal
    Description: open
    Keywords: sudden stratospheric warming ; winter polar stratosphere ; temperature ; O3 ; N2O ; CO ; 01. Atmosphere::01.01. Atmosphere::01.01.01. Composition and Structure ; 01. Atmosphere::01.01. Atmosphere::01.01.04. Processes and Dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 4
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    High-speed imaging of Strombolian explosions: The ejection velocity of pyroclasts (2015)
    American Geophysical Union
    Details
    Publication Date: 2020-12-14
    Description: Explosive volcanic eruptions are defined as the violent ejection of gas and hot fragments from a vent in the Earth's crust. Knowledge of ejection velocity is crucial for understanding and modeling relevant physical processes of an eruption, and yet direct measurements are still a difficult task with largely variable results. Here we apply pioneering high-speed imaging to measure the ejection velocity of pyroclasts from Strombolian explosive eruptions with an unparalleled temporal resolution. Measured supersonic velocities, up to 405 m/s, are twice higher than previously reported for such eruptions. Individual Strombolian explosions include multiple, sub-second-lasting ejection pulses characterized by an exponential decay of velocity. When fitted with an empirical model from shock-tube experiments literature, this decay allows constraining the length of the pressurized gas pockets responsible for the ejection pulses. These results directly impact eruption modeling and related hazard assessment, as well as the interpretation of geophysical signals from monitoring networks.
    Description: INGV-DPC “V2” and “Paroxysm”, FIRB-MIUR “Research and Development of New Technologies for Protection and Defense of Territory from Natural Risks”, and FP7-PEOPLE-IEF-2008 – 235328 Projects
    Description: Published
    Description: L02301
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: open
    Keywords: strombolian ; ejection velocity ; explosive eruption ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques ; 05. General::05.02. Data dissemination::05.02.03. Volcanic eruptions
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Insights into shallow magmatic processes at Kīlauea Volcano, Hawaiʻi, from a multiyear continuous gravity time series (2017)
    American Geophysical Union
    Details
    Publication Date: 2021-02-10
    Description: Continuous gravity data collected near the summit eruptive vent at Kīlauea Volcano, Hawaiʻi, during 2011–2015 show a strong correlation with summit-area surface deformation and the level of the lava lake within the vent over periods of days to weeks, suggesting that changes in gravity reflect variations in volcanic activity. Joint analysis of gravity and lava level time series data indicates that over the entire time period studied, the average density of the lava within the upper tens to hundreds of meters of the summit eruptive vent remained low—approximately 1000–1500 kg/m^3. The ratio of gravity change (adjusted for Earth tides and instrumental drift) to lava level change measured over 15 day windows rose gradually over the course of 2011–2015, probably reflecting either (1) a small increase in the density of lava within the eruptive vent or (2) an increase in the volume of lava within the vent due to gradual vent enlargement. Superimposed on the overall time series were transient spikes of mass change associated with inflation and deflation of Kīlauea’s summit and coincident changes in lava level. The unexpectedly strong mass variations during these episodes suggest magma flux to and from the shallow magmatic system without commensurate deformation, perhaps indicating magma accumulation within, and withdrawal from, void space—a process that might not otherwise be apparent from lava level and deformation data alone. Continuous gravity data thus provide unique insights into magmatic processes, arguing for continued application of the method at other frequently active volcanoes.
    Description: Published
    Description: 5477–5492
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Kīlauea Volcano; gravity changes; lava lake; volcano monitoring ; 04. Solid Earth::04.02. Exploration geophysics::04.02.02. Gravity methods ; 04. Solid Earth::04.03. Geodesy::04.03.05. Gravity variations ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 6
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    The borehole dilatometers network of Mt. Etna : a powerful tool to detect and infer volcano dynamics (2017)
    American Geophysical Union
    Details
    Publication Date: 2021-02-10
    Description: A network of four borehole dilatometers has been installed on Etna in two successive phases (2010–2011 and 2014). The borehole dilatometers are installed in holes drilled at depths usually greater than 100 m, and they measure the volumetric strain of the surrounding rock with a nominal precision up to 10^-11 in a wide frequency range (10^-7–25 Hz). Here we describe the characteristics of the network and the results of the in situ calibrations obtained after the installations by different methods. We illustrate short-term strain changes recorded during several lava fountains erupted by Etna during 2011–2013, and we also show signal changes recorded at all four stations during the lava fountain on 28 December 2014. Analytical and numerical computations constrained the eruptions source depth and also its volume change that is related to the magma volume emitted. Finally, we show the potential of the signal in the medium term to reveal strain changes related to different phases of the volcanic activity.
    Description: Published
    Description: 4655–4669
    Description: 1IT. Reti di monitoraggio e Osservazioni
    Description: JCR Journal
    Description: restricted
    Keywords: Etna volcano ; borehole strainmeters ; strain ; eruptions and lava fountains ; 04. Solid Earth::04.06. Seismology::04.06.06. Surveys, measurements, and monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 7
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    Eruptive activity at Turrialba volcano (Costa Rica): Inferences from 3He/4He in fumarole gases and chemistry of the products ejected during 2014 and 2015 (2017)
    American Geophysical Union
    Details
    Publication Date: 2021-03-01
    Description: A new period of eruptive activity started at Turrialba volcano, Costa Rica, in 2010 after almost 150 years of quiescence. This activity has been characterized by sporadic explosions whose frequency clearly increased since October 2014. This study aimed to identify the mechanisms that triggered the resumption of this eruptive activity and characterize the evolution of the phenomena over the past 2 years. We integrate 3He/4He data available on fumarole gases collected in the summit area of Turrialba between 1999 and 2011 with new measurements made on samples collected between September 2014 and February 2016. The results of a petrological investigation of the products that erupted between October 2014 and May 2015 are also presented. We infer that the resumption of eruptive activity in 2010 was triggered by a replenishment of the plumbing system of Turrialba by a new batch of magma. This is supported by the increase in 3He/4He values observed since 2005 at the crater fumaroles and by comparable high values in September 2014, just before the onset of the new eruptive phase. The presence of a number of fresh and juvenile glassy shards in the erupted products increased between October 2014 and May 2015, suggesting the involvement of new magma with a composition similar to that erupted in 1864–1866. We conclude that the increase in 3He/4He at the summit fumaroles since October 2015 represents strong evidence of a new phase of magma replenishment, which implies that the level of activity remains high at the volcano.
    Description: Published
    Description: 3V. Proprietà dei magmi e dei prodotti vulcanici
    Description: 4V. Dinamica dei processi pre-eruttivi
    Description: 5V. Dinamica dei processi eruttivi e post-eruttivi
    Description: JCR Journal
    Keywords: Turrialba volcano ; eruptive activity ; 3He/4He ; fumarole gases ; glassy shards ; juvenile component ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.07. Tectonophysics::04.07.08. Volcanic arcs ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas ; 04. Solid Earth::04.08. Volcanology::04.08.05. Volcanic rocks ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 8
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    Retrospective short-term forecasting experiment in Italy based on the occurrence of strong (fore) shocks (2021)
    Oxford University Press
    Details
    Publication Date: 2021-03-15
    Description: In a recent work we computed the relative frequencies with which strong shocks (4.0≤Mw〈5.0), widely felt by the population were followed in the same area by potentially destructive main shocks (Mw≥5.0) in Italy. Assuming the stationarity of the seismic release properties, such frequencies can be tentatively used to estimate the probabilities of potentially destructive shocks after the occurrence of future strong shocks. This allows us to set up an alarm-based forecasting hypothesis related to strong foreshocks occurrence. Such hypothesis is tested retrospectively on the data of a homogenized seismic catalogue of the Italian area against a purely random hypothesis that simply forecasts the target main shocks proportionally to the space-time fraction occupied by the alarms. We compute the latter fraction in two ways a) as the ratio between the average time covered by the alarms in each area and the total duration of the forecasting experiment (60 years) and b) as the same ratio but weighted by the past frequency of occurrence of earthquakes in each area. In both cases the overall retrospective performance of our forecasting algorithm is definitely better than the random case. Considering an alarm duration of three months, the algorithm retrospectively forecasts more than 70% of all shocks with Mw5.5 occurred in Italy from 1960 to 2019 with a total space-time fraction covered by the alarms of the order of 2%. Considering the same space-time coverage, the algorithm is also able to retrospectively forecasts more than 40% of the first main shocks with Mw5.5 of the seismic sequences occurred in the same time interval. Given the good reliability of our results, the forecasting algorithm is set and ready to be tested also prospectively, in parallel to other ongoing procedures operating on the Italian territory.
    Description: This paper benefitted from funding provided by the European Union within the ambit of the H2020 project RISE (No. 821115), which in particular fully financed the PhD grant of one of the authors (E.B.).
    Description: Published
    Description: 1192–1206
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
    Keywords: Earthquake interaction ; Statistical seismology ; forecasting, ; prediction ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 9
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    The September 26, 1997 Colfiorito, Italy Earthquakes: modeled coseismic surface displacement from SAR interferometry and GPS (2012)
    American Geophysical Union
    Details
    Publication Date: 2021-05-25
    Description: The largest events of the 1997 Umbria-Marche sesimic sequence were the two September 26 earthquakes of Mw=5.7 (00:33 GMT) and Mw=6.0 (09:40 GMT), which caused severe damage and ground cracks in a wide area around the epicenters. We created an ERS-SAR differenrtial interferogram, where nine fringes are visible in and around the Colfiorito basin, corresponding to 25 cm of coseismic surface dispalacements. GPS data show a maximum horizontal displacement...
    Description: Published
    Description: 883-886
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: restricted
    Keywords: Colfiorito, SAR, GPS ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 10
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    An unloading foam model to constrain Etna’s 11–13 January 2011 lava fountaining episode (2011)
    American Geophysical Union
    Details
    Publication Date: 2021-06-09
    Description: The 11–13 January 2011 eruptive episode at Etna volcano occurred after several months of increasing ash emissions from the summit craters, and was heralded by increasing SO2 output, which peaked at ∼5000 megagrams/day several hours before the start of the eruptive activity. The eruptive episode began with a phase of Strombolian activity from a pit crater on the eastern flank of the SE‐Crater. Explosions became more intense with time and eventually became transitional between Strombolian and fountaining, before moving into a lava fountaining phase. Fountaining was accompanied by lava output from the lower rim of the pit crater. Emplacement of the resulting lava flow field, as well as associated lava fountain‐ and Strombolian‐phases, was tracked using a remote sensing network comprising both thermal and visible cameras. Thermal surveys completed once the eruptive episode had ended also allowed us to reconstruct the emplacement of the lava flow field. Using a high temporal resolution geostationary satellite data we were also able to construct a detailed record of the heat flux during the fountain‐fed flow phase and its subsequent cooling. The dense rock volume of erupted lava obtained from the satellite data was 1.2 × 106 m3; this was emplaced over a period of about 6 h to give a mean output rate of ∼55 m3 s−1. By comparison, geologic data allowed us to estimate dense rock volumes of ∼0.85 × 106 m3 for the pyroclastics erupted during the lava fountain phase, and 0.84–1.7 × 106 m3 for lavas erupted during the effusive phase, resulting in a total erupted dense rock volume of 1.7–2.5 × 106 m3 and a mean output rate of 78–117 m3 s−1. The sequence of events and quantitative results presented here shed light on the shallow feeding system of the volcano.
    Description: Published
    Description: B11207
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: partially_open
    Keywords: Etna ; lava fountains ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 11
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    A year of lava fountaining at Etna: Volumes from SEVIRI (2012)
    American Geophysical Union
    Details
    Publication Date: 2021-06-09
    Description: We present a new method that uses cooling curves, apparent in high temporal resolution thermal data acquired by geostationary sensors, to estimate erupted volumes and mean output rates during short lava fountaining events. The 15 minute temporal resolution of the data allows phases of waxing and peak activity to be identified during short (150-to- 810 minute-long) events. Cooling curves, which decay over 8-to-21 hour-periods following the fountaining event, can also be identified. Application to 19 fountaining events recorded at Etna by MSG’s SEVIRI sensor between 10 January 2011 and 9 January 2012, yields a total erupted dense rock lava volume of 28 106 m3, with a maximum intensity of 227 m3 s 1 being obtained for the 12 August 2011 event. The timeaveraged output over the year was 0.9 m3 s 1, this being the same as the rate that has characterized Etna’s effusive activity for the last 40 years.
    Description: We are grateful to EUMETSAT for SEVIRI data.
    Description: Published
    Description: L06305
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: restricted
    Keywords: satellite ; lava fountains ; Etna ; erupted volume ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 12
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    Thermal structure of a vanishing subduction system. An example of seismically-derived crustal temperature along the Italian peninsula (2020)
    Oxford University Press
    Details
    Publication Date: 2020-10-16
    Description: This article has been accepted for publication in Geophysical Journal International ©: The Authors 2019. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy.
    Description: The active tectonic processes in convergent margins confer a high degree of complexity to the crust. Determining the thermal structure is, therefore, key to better elucidate the nature of those processes. In order to reconstruct the thermal structure of the crust beneath the Italian peninsula, we combine the most recent and accurate shear-wave velocity model that is currently available with thermodynamic modelling, assuming a global average crustal composition with no lateral variations. Our model, presented in terms of Moho temperature and crustal thermal gradients, shows a very good agreement with the known thermal anomalies associated with the backarc spreading related to the Apennine subduction. Importantly, we envisage a new anomalous region of high Moho temperatures in NW Italy (T 〉 800 degrees C at 30 km), at the transition between the Alps and Apennine orogens. The lowest temperatures of our model, corresponding to geothermal gradients 〈 19 degrees C km(-1), are obtained in the still active but slow-convergent portion of the northern Apennine. Moho temperatures increase moving southwards along the Apennine chain, an observation that is coherent with the evidence of ceasing subduction and consequent rebalancing of the depressed isotherms along the slab. Our results suggest that a thermal structure in different tectonic settings can be inferred with acceptable uncertainties based on absolute seismic velocity models. In this sense, our approach can be extended to any other region.
    Description: Published
    Description: 239–247
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 13
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    Magma andVolatile Supply to Post-collapse Volcanism and Block Resurgence in Siwi Caldera (Tanna Island,Vanuatu Arc) (2011)
    Oxford University Press
    Details
    Publication Date: 2020-11-20
    Description: Siwi caldera, in the Vanuatu arc (Tanna island), is a rare volcanic complex where both persistent eruptive activity (Yasur volcano)and rapid block resurgence (Yenkahe horst) can be investigated simultaneously during a post-caldera stage. Here we provide new constraints on the feeding system of this volcanic complex, based on a detailed study of the petrology, geochemistry and volatile content of Yasur^Siwi bulk-rocks and melt inclusions, combined with measurements of the chemical composition and mass fluxes of Yasur volcanic gases. Major and trace element analyses of Yasur^ Siwi volcanic rocks, together with literature data for other volcanic centers, point to a single magmatic series and possibly long-lived feeding of Tanna volcanism by a homogeneous arc basalt. Olivine-hosted melt inclusions show that the parental basaltic magma, which produces basaltic-trachyandesites to trachyandesites by 50^70% crystal fractionation, is moderately enriched in volatiles ( 1wt % H2O, 0·1wt % S and 0·055 wt % Cl). The basaltic-trachyandesite magma, emplaced at between 4^5 km depth and the surface, preserves a high temperature (1107 158C) and constant H2O content ( 1wt %) until very shallow depths, where it degasses extensively and crystallizes. These conditions, maintained over the past 1400 years of Yasur activity, require early water loss during basalt differentiation, prevalent open-system degassing, and a relatively high heat flow ( 109W). Yasur volcano releases on average 13·4 103 tons d 1 of H2O and 680 tons d 1 of SO2, but moderate amounts of CO2 (840 tons d 1), HCl (165 tons d 1), and HF (23 tons d 1). Combined with melt inclusion data, these gas outputs constrain a bulk magma degassing rate of 5 107 m3 a 1, about a half of which is due to degassing of the basaltic-trachyandesite. We compute that 25 km3 of this magma have degassed without erupting and have accumulated beneath Siwi caldera over the past 1000 years, which is one order of magnitude larger than the accumulated volume uplift of the Yenkahe resurgent block. Hence, basalt supply and gradual storage of unerupted degassed basaltictrachyandesite could easily account for (or contribute to) the Yenkahe block resurgence.
    Description: Published
    Description: 1077-1105
    Description: 2.3. TTC - Laboratori di chimica e fisica delle rocce
    Description: 2.4. TTC - Laboratori di geochimica dei fluidi
    Description: JCR Journal
    Description: restricted
    Keywords: Vanuatu arc ; Yasur ; gas fluxes ; volatiles ; melt inclusions ; resurgent block ; volcano thermal budget ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases ; 04. Solid Earth::04.08. Volcanology::04.08.03. Magmas
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  • 14
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    Turbulent times in the northern polar ionosphere? (2011)
    American Geophysical Union
    Details
    Publication Date: 2020-12-03
    Description: A model is presented of the growth rate of turbulently generated irregularities in the electron concentration of northern polar cap plasma patches. The turbulence is generated by the short‐term fluctuations in the electric field imposed on the polar cap ionosphere by electric field mapping from the magnetosphere. The model uses an ionospheric imaging algorithm to specify the state of the ionosphere throughout. The growth rates are used to estimate mean amplitudes for the irregularities, and these mean amplitudes are compared with observations of the scintillation indices S4 and s by calculating the linear correlation coefficients between them. The scintillation data are recorded by GPS L1 band receivers stationed at high northern latitudes. A total of 13 days are analyzed, covering four separate magnetic storm periods. These results are compared with those from a similar model of the gradient drift instability (GDI) growth rate. Overall, the results show better correlation between the GDI process and the scintillation indices than for the turbulence process and the scintillation indices. Two storms, however, show approximately equally good correlations for both processes, indicating that there might be times when the turbulence process of irregularity formation on plasma patches may be the controlling one.
    Description: Published
    Description: A04310
    Description: 1.7. Osservazioni di alta e media atmosfera
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: JCR Journal
    Description: restricted
    Keywords: ionospheric irregularities ; scintillations ; Gradient Drift Instability ; 01. Atmosphere::01.02. Ionosphere::01.02.04. Plasma Physics ; 01. Atmosphere::01.02. Ionosphere::01.02.07. Scintillations ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
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  • 15
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    Synchronization between tides and sustained oscillations of the hydrothermal system of Campi Flegrei (Italy) (2013)
    American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: Long continuous seismic data recorded at five broadband seismic stations during 2006 at Campi Flegrei caldera have been analyzed. Introducing a coarse-grained method, we evaluate the time evolution of amplitude and polarization of the seismic noise in the frequency band common to long-period events. The series are modulated on tidal time scales: the root-mean square is basically dominated by solar contribution, while the azimuth of the polarization vector shows lunar diurnal and semidiurnal constituents. In addition, we find that in the frequency band common to long-period events the azimuths are polarized toward a specific area, suggesting that these persistent oscillations can be induced by the activity of the shallow geothermal reservoir.
    Description: Published
    Description: 2628–2637
    Description: JCR Journal
    Description: restricted
    Keywords: sustained hydrothermal tremor ; Campi Flegrei Caldera ; polarization analysis ; tidal modulation ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
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  • 16
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    Spatially resolved SO2 flux emissions from Mt Etna (2017)
    American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: We report on a systematic record of SO2 flux emissions from individual vents of Etna volcano (Sicily), which we obtained using a permanent UV camera network. Observations were carried out in summer 2014, a period encompassing two eruptive episodes of the New South East Crater (NSEC) and a fissure-fed eruption in the upper Valle del Bove. We demonstrate that our vent-resolved SO2 flux time series allow capturing shifts in activity from one vent to another and contribute to our understanding of Etna’s shallowplumbingsystemstructure.We findthatthe fissureeruptioncontributed~50,000tofSO2 or~30%of the SO2 emitted by the volcano during the 5 July to 10 August eruptive interval. Activity from this eruptive ventgraduallyvanishedon10August,markingaswitchofdegassingtowardtheNSEC.Onsetofdegassingat the NSEC was a precursory to explosive paroxysmal activity on 11–15 August.
    Description: Published
    Description: 7511-7519
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Records of SO2 flux emissions from Etna’sindividualventsallowcapturing shifts in volcanic activity ; Vent-resolved SO2 flux time series provide constraints on geometry of the shallow plumbing system ; Vent-resolved SO2 flux time series demonstrate SO2 flux increase precursory to paroxysmal (lava fountaining) activity ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
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  • 17
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    Mapping Moho depth variations in central Italy from PsMoho-P delay times: Evidence of an E-W transition in the Adriatic Moho at 42°N latitude (2014)
    American Geophysical Union
    Details
    Publication Date: 2020-12-18
    Description: Along the Italian peninsula adjoin two crustal domains, peri-Tyrrhenian and Adriatic, whose boundary is not univocal in central Italy. In this area, we attempt to map the extent of the Moho in the two terrains from variations of the travel time difference between the direct P wave and the P-to-S wave converted at the crust-mantle boundary, called PsMoho. We use teleseismic receiver functions computed at 38 broad-band stations in this and previous studies, and assigned each of the recording sites to the Adriatic or peri-Tyrrhenian terrains based on station location, geologic and geophysical data and interpretation, and consistency of delays with the regional Moho trend. The results of the present study show that the PsMoho arrival time varies from 2.3 to 4.1 s in the peri-Tyrrhenian domain and from 3.7 to 5.5 s in the Adriatic domain. As expected, the lowest time difference is observed along the Tyrrhenian coastline and the largest values are observed in the axial zone of the Apennine chain. A key new result of this study is a sharp E-W boundary in the Adriatic domain that separates a deeper Moho north of about 42 N latitude from a shallower Moho to the south. This feature is constrained for a length of about 40 km by the observations available in this study. The E-W boundary requires a revision of prior mapping of the Moho in central Italy and supports previous hypotheses of lithosphere segmentation.
    Description: Published
    Description: 3929–3938
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: open
    Keywords: teleseismic receiver functions ; Moho discontinuity ; central Italy ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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  • 18
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    Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy (2020)
    Oxford University Press
    Details
    Publication Date: 2020-12-15
    Description: This article has been accepted for publication in Geophysical Journal International ©: The Authors 2015. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Uploaded in accordance with the publisher's self-archiving policy.
    Description: ectonic earthquake swarms challenge our understanding of earthquake processes since it is difficult to link observations to the underlying physical mechanisms and to assess the hazard they pose. Transient forcing is thought to initiate and drive the spatio-temporal release of energy during swarms. The nature of the transient forcing may vary across sequences and range from aseismic creeping or transient slip to diffusion of pore pressure pulses to fluid redistribution and migration within the seismogenic crust. Distinguishing between such forcing mechanisms may be critical to reduce epistemic uncertainties in the assessment of hazard due to seismic swarms, because it can provide information on the frequency–magnitude distribution of the earthquakes (often deviating from the assumed Gutenberg–Richter relation) and on the expected source parameters influencing the ground motion (for example the stress drop). Here we study the ongoing Pollino range (Southern Italy) seismic swarm, a long-lasting seismic sequence with more than five thousand events recorded and located since October 2010. The two largest shocks (magnitude M w = 4.2 and M w = 5.1) are among the largest earthquakes ever recorded in an area which represents a seismic gap in the Italian historical earthquake catalogue. We investigate the geometrical, mechanical and statistical characteristics of the largest earthquakes and of the entire swarm. We calculate the focal mechanisms of the M l 〉 3 events in the sequence and the transfer of Coulomb stress on nearby known faults and analyse the statistics of the earthquake catalogue. We find that only 25 per cent of the earthquakes in the sequence can be explained as aftershocks, and the remaining 75 per cent may be attributed to a transient forcing. The b-values change in time throughout the sequence, with low b-values correlated with the period of highest rate of activity and with the occurrence of the largest shock. In the light of recent studies on the palaeoseismic and historical activity in the Pollino area, we identify two scenarios consistent with the observations and our analysis: This and past seismic swarms may have been ‘passive’ features, with small fault patches failing on largely locked faults, or may have been accompanied by an ‘active’, largely aseismic, release of a large portion of the accumulated tectonic strain. Those scenarios have very different implications for the seismic hazard of the area.
    Description: Published
    Description: 1553–1567
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
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  • 19
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    Non-stability of the noise HVSR at sites near or on topographic heights (2021)
    Oxford University Press
    Details
    Publication Date: 2021-01-18
    Description: The horizontal to vertical spectral ratio (HVSR) of seismic noise is often used to investigate site effects, and it is usually assumed to be a stable feature of the site considered. Here we show that such an assumption is not always justified, and may lead to incorrect conclusions. The HVSR analysis was performed on ambient seismic noise recordings lasting from weeks to months at many sites in Calabria, Italy. Results show a variety of site effects, from the resonance of a shallow sedimentary layer to the polarized amplification of horizontal ground motion associated with topographic effects. We describe the results of seven sites whose HVSR is characterized by dual content: one that is persistent, and another appearing only occasionally. Two sites very near the coast of the Tyrrhenian sea and five sites in the Calabrian Arc mountains show the most remarkable results. The shape of the HVSR changes significantly at these sites when the amplitude of background noise increases in a broad frequency band during periods of bad weather. The occasional contribution to the HVSR consists of one or more peaks, depending on the site, that appear only when the amplitude of ambient noise is higher than usual. The seven sites where we observe the HVSR variability are all located in complex geological environments, on mountains, ridges or foothills. A variation of the HVSR correlated with the day–night cycle is also observed at some of these sites.
    Description: Published
    Description: 2162–2171
    Description: 1T. Struttura della Terra
    Description: JCR Journal
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  • 20
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    Low-temperature magnetic properties of pelagic carbonates: Oxidation of biogenic magnetite and identification of magnetosome chains (2014)
    American Geophysical Union
    Details
    Publication Date: 2021-02-17
    Description: Pelagic marine carbonates provide important records of past environmental change. We carried out detailed low-temperature magnetic measurements on biogenic magnetite-bearing sediments from the Southern Ocean (Ocean Drilling Program (ODP) Holes 738B, 738C, 689D, and 690C) and on samples containing whole magnetotactic bacteria cells. We document a range of low-temperature magnetic properties, including reversible humped low-temperature cycling (LTC) curves. Different degrees of magnetite oxidation are considered to be responsible for the observed variable shapes of LTC curves. A dipole spring mechanism in magnetosome chains is introduced to explain reversible LTC curves. This dipole spring mechanism is proposed to result from the uniaxial anisotropy that originates from the chain arrangement of biogenic magnetite, similar to published results for uniaxial stable single domain (SD) particles. The dipole spring mechanism reversibly restores the remanence during warming in LTC measurements. This supports a previous idea that remanence of magnetosome chains is completely reversible during LTC experiments. We suggest that this magnetic fingerprint is a diagnostic indicator for intact magnetosome chains, although the presence of isolated uniaxial stable SD particles and magnetically interacting particles can complicate this test. Magnetic measurements through the Eocene section of ODP Hole 738B reveal an interval with distinct magnetic properties that we interpret to originate from less oxidized biogenic magnetite and enrichment of a biogenic “hard” component. Co-occurrence of these two magnetic fingerprints during the late Eocene in the Southern Ocean indicates less oxic conditions, probably due to increased oceanic primary productivity and organic carbon burial.
    Description: Published
    Description: 6049–6065
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: pelagic carbonates ; biogenic magnetite ; rock magnetism ; environmental magnetism ; ODP ; 04. Solid Earth::04.04. Geology::04.04.08. Sediments: dating, processes, transport ; 04. Solid Earth::04.05. Geomagnetism::04.05.09. Environmental magnetism
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  • 21
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    The annual asymmetry in the F2 layer during deep solar minimum (2008–2009): December anomaly (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-02-10
    Description: Annual January/July midlatitude daytime asymmetry in monthly median NmF2 and model thermospheric parameters has been considered during deep solar minimum, (2008–2009), when solar and geomagnetic activities were at the lowest level, to analyze the background effect due to the Sun-Earth minimum distance, perihelion, in the vicinity of the December solstice. Averaged over 10 midlatitude station pairs, the NmF2 asymmetry was found to be ≈1.23, while the average asymmetry for the annual component in NmF2 variations is ≈1.17. Annual asymmetry in monthly median neutral composition and temperature predicted by Mass Spectrometer Incoherent Scatter 86 (MSIS86) and MSISE00 thermospheric models along with the 7% increase in solar EUV flux in the vicinity of the December solstice is sufficient to explain the observed annual asymmetry in NmF2. A hierarchy of aeronomic parameters responsible for the observed asymmetry in NmF2 has been established: the main contributor is atomic oxygen—about 50% of the total effect, [N2] contributes around 35% strongly compensating the [O] contribution, and solar EUV and Tn provide 〈10% each. The zonal mean annual asymmetry in MSIS86 atomic oxygen column density was shown to be 1.18 at low and middle latitudes, and this is close to the estimated asymmetry for the annual component in NmF2 variations. The earlier proposed mechanism of the December anomaly is considered as a plausible one to explain the 1.18 January/July asymmetry in the atomic oxygen variations and consequently the NmF2 annual daytime asymmetry at middle latitudes under the deep solar minimum.
    Description: Published
    Description: 1341-1354
    Description: 2A. Fisica dell'alta atmosfera
    Description: JCR Journal
    Description: restricted
    Keywords: december anomaly ; 01. Atmosphere::01.02. Ionosphere::01.02.01. Ion chemistry and composition
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  • 22
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    The Shallow Plumbing System of Piton de la Fournaise Volcano (La Reunion Island, Indian Ocean) Revealed by the Major 2007 Caldera-Forming Eruption (2021)
    Oxford University Press
    Details
    Publication Date: 2021-02-10
    Description: The 2007 caldera-forming eruption of Piton de la Fournaise (PdF) erupted the largest volume of magma (210 Mm3)recorded at this volcano in at least three centuries. Major and trace element and Sr^Nd isotope data for bulk-rocks, groundmasses and olivine phenocrysts have been combined with melt inclusion data (major, trace and volatile elements) to track magma evolution over the whole eruptive sequence. We show that each eruptive phase had a distinctive geochemical and petrological signature and that caldera collapse on 5 April was preceded by a marked shift in bulk magma composition and crystal content and size. Aphyric basalt erupted at the beginning of the sequence (February 2007) had relatively high Sr isotope ratio (87Sr/86Sr ¼ 0·70420^0·704180) and low Nd isotopic ratio(143Nd/144Nd ¼ 0·51285^0·51286). Olivine-basalts extruded on2^5 April just before caldera collapse are less enriched in radiogenic Sr (87Sr/86Sr ¼ 0·70412^0·70416), but characterized by the same Nd isotopic composition. This magma is interpreted as a new deep input, which pressurized the shallow PdF plumbing system and triggered the 2007 activity. Post-collapse oceanite lavas represent the main volume of magma extruded in 2007. Their bulk-rocks and groundmasses have 87Sr/86Sr (0·70418) intermediate between those of February and 5 April, and similar to those of the March 2007 and 2001^2006 lavas.We show that the Steady State Basalts (SSB) commonly erupted at PdF are hybrid melts, which result from multistep mixing between ‘alkaline’and ‘transitional’end-members. Our results lead us to propose a new model of the PdF plumbing system to reconcile the petrological, geochemical and geophysical observations: (1) the shallow portion (above sea level) of the PdF plumbing system hosts several small sills, in which magma experiences variable degrees of degassing, cooling and crystallization; (2) oceanite lavas result from the withdrawal of shallow harrisitic mushes stored at low pressures (548 MPa; 51800^2400 m depth) below both the volcano summit and its eastern flank; (3) water degassing plays a major role in fast magma crystallization at shallow depths. Multistep ascent and periodic extrusion of the shallow magmas is promoted by injections of deeper and hotter basaltic magma, containing up to 1·3 wt % H2O and 1630 ppm S. In 2007, the new deep input was the ultimate source of the large excess in sulfur degassing detected by satellites. Lateral draining and intrusion of magma below the eastern flank of the volcano are the cause of major volcano deformation, flank sliding and summit caldera collapse.
    Description: Published
    Description: 1287-1315
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: 4V. Processi pre-eruttivi
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: Piton de la Fournaise ; plumbing system ; magma reservoir ; caldera collapse ; melt inclusions ; volatile budget ; isotope geochemistry ; basalt
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  • 23
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    Numerical analysis of interseismic, coseismic and postseismic phases for normal and reverse faulting earthquakes in Italy (2021)
    Oxford University Press
    Details
    Publication Date: 2021-02-23
    Description: The preparation, initiation, and occurrence dynamics of earthquakes in Italy are governed by several frequently unknown physical mechanisms and parameters. Understanding these mechanisms is crucial for developing new techniques and approaches for earthquake monitoring and hazard assessments. Here, we develop a first-order numerical model simulating quasi-static crustal interseismic loading, coseismic brittle episodic dislocations, and postseismic relaxation for extensional and compressional earthquakes in Italy based on a common framework of lithostatic and tectonic forces. Our model includes an upper crust, where the fault is locked, and a deep crust, where the fault experiences steady shear.
    Description: Published
    Description: 627–645
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
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  • 24
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    An automatically generated high-resolution earthquake catalogue for the 2016–2017 Central Italy seismic sequence, including P and S phase arrival times (2021)
    Oxford University Press
    Details
    Publication Date: 2021-03-24
    Description: The 2016–17 central Italy earthquake sequence began with the first mainshock near the town of Amatrice on August 24 (MW 6.0), and was followed by two subsequent large events near Visso on October 26 (MW 5.9) and Norcia on October 30 (MW 6.5), plus a cluster of 4 events with MW 〉 5.0 within few hours on January 18, 2017. The affected area had been monitored before the sequence started by the permanent Italian National Seismic Network (RSNC), and was enhanced during the sequence by temporary stations deployed by the National Institute of Geophysics and Volcanology and the British Geological Survey. By the middle of September, there was a dense network of 155 stations, with a mean separation in the epicentral area of 6–10 km, comparable to the most likely earthquake depth range in the region. This network configuration was kept stable for an entire year, producing 2.5 TB of continuous waveform recordings. Here we describe how this data was used to develop a large and comprehensive earthquake catalogue using the Complete Automatic Seismic Processor (CASP) procedure. This procedure detected more than 450,000 events in the year following the first mainshock, and determined their phase arrival times through an advanced picker engine (RSNI-Picker2), producing a set of about 7 million P- and 10 million S-wave arrival times. These were then used to locate the events using a non-linear location (NLL) algorithm, a 1D velocity model calibrated for the area, and station corrections and then to compute their local magnitudes (ML). The procedure was validated by comparison of the derived data for phase picks and earthquake parameters with a handpicked reference catalogue (hereinafter referred to as ‘RefCat’). The automated procedure takes less than 12 hours on an Intel Core-i7 workstation to analyse the primary waveform data and to detect and locate 3000 events on the most seismically active day of the sequence. This proves the concept that the CASP algorithm can provide effectively real-time data for input into daily operational earthquake forecasts, The results show that there have been significant improvements compared to RefCat obtained in the same period using manual phase picks. The number of detected and located events is higher (from 84,401 to 450,000), the magnitude of completeness is lower (from ML 1.4 to 0.6), and also the number of phase picks is greater with an average number of 72 picked arrival for a ML = 1.4 compared with 30 phases for RefCat using manual phase picking. These propagate into formal uncertainties of ± 0.9km in epicentral location and ± 1.5km in depth for the enhanced catalogue for the vast majority of the events. Together, these provide a significant improvement in the resolution of fine structures such as local planar structures and clusters, in particular the identification of shallow events occurring in parts of the crust previously thought to be inactive. The lower completeness magnitude provides a rich data set for development and testing of analysis techniques of seismic sequences evolution, including real-time, operational monitoring of b-value, time-dependent hazard evaluation and aftershock forecasting.
    Description: Published
    Description: 555–571
    Description: 3T. Fisica dei terremoti e Sorgente Sismica
    Description: JCR Journal
    Keywords: 04.06. Seismology
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    Erratum: On seismic ambient noise cross-correlation and surface-wave attenuation (2021)
    Oxford University Press
    Details
    Publication Date: 2021-05-12
    Description: erratum paper
    Description: Published
    Description: 1090-1092
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: Theoretical seismology ; Seismic attenuation ; Seismic noise ; Surface waves ; Free oscillations ; Seismic interferometry ; 04.06. Seismology ; 04.01. Earth Interior
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  • 26
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    Crustal structure of the Azores Archipelago from Rayleigh wave ellipticity data (2021)
    Oxford University Press
    Details
    Publication Date: 2021-05-12
    Description: This article has been accepted for publication inGeophysical Journal International ©The Author(s) 2020. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
    Description: Determining the crustal structure of ocean island volcanoes is important to understand the formation and tectonic evolution of the oceanic lithosphere and tectonic swells in marine settings, and to assess seismic hazard in the islands. The Azores Archipelago is located near a triple junction system and is possibly under the influence of a mantle plume, being at the locus of a wide range of geodynamic processes. However, its crustal structure is still poorly constrained and debated due to the limited seismic coverage of the region and the peculiar linear geometry of the islands. To address these limitations, in this study we invert teleseismic Rayleigh wave ellipticity measurements for 1-D shear wave speed (VS) crustal models of the Azores Archipelago. Moreover, we test the reliability of these new models by using them in independent moment tensor inversions of local seismic data and demonstrate that our models improve the waveform fit compared to previous models. We find that data from the westernmost seismic stations used in this study require a shallower Moho depth (∼10 km) than data from stations in the eastern part of the archipelago (∼13–16 km). This apparent increase in the Moho depth with increasing distance from the mid-Atlantic ridge (MAR) is expected. However, the rate at which Moho deepens away from the MAR is greater than that predicted from a half-space cooling model, suggesting that local tectonic perturbations have modified crustal structure. The 1-D VS models obtained beneath the westernmost seismic stations also show higher wave speeds than for the easternmost stations, which correlates well with the ages of the islands except Santa Maria Island. We interpret the relatively low VS profile found beneath Santa Maria Island as resulting from underplating, which agrees with previous geological studies of the island. Compared to a recent receiver function study of the region, the shallow structure (top ∼2 km) in our models shows lower shear wave speed, which may have important implications for future hazard studies of the region. More generally, the new seismic crustal models we present in this study will be useful to better understand the tectonics, seismicity, moment tensors and strong ground motions in the region.
    Description: Published
    Description: 1232–1247
    Description: 5T. Sismologia, geofisica e geologia per l'ingegneria sismica
    Description: JCR Journal
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  • 27
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    Changing modes and rates of mafic magma supply at Pantelleria (Sicily Channel, Southern Italy): new perspectives on the volcano factory drawn upon olivine records (2021)
    Oxford University Press
    Details
    Publication Date: 2021-05-12
    Description: The island of Pantelleria, located in the Sicily Channel Rift Zone (Italy), has been the site of violent peralkaline silicic magmatism alternating with minor effusive to low-intensity Strombolian erup- tions of basaltic composition. The basaltic rock suites exposed on the island were sampled to in- vestigate the plumbing system dynamics through the study of chemical stratigraphy and temporal records of olivine crystals. Our petrographic and geochemical observations, together with the com- positional variability of olivine, suggest different evolutionary histories for basaltic magmas erupted over two major periods divided by the 􏰃45 ka Green Tuff (GT) eruption. Core-to-rim com- positional traverses across olivine crystals document different types of zoning. We recognized oliv- ine zones affected by Fo oscillations at very fine scales in the inner cores, rims and/or in intermedi- ate portions of crystals and used them to reconstruct the residence and passage of crystals through different magmatic environments, with P–T–ƒO2 and compositional characteristics con- strained by thermodynamic modeling. The sequence of magmatic environments evidenced by oliv- ine zoning indicate that the pre-GT volcanic period was dominated by injection at shallow crustal levels (􏰃300–200 MPa) of primitive melts, initially moving from a deep storage zone at the crust- mantle boundary. Supply of this magma significantly decreased after the GT eruption, while the dy- namics of magma transfer within the upper portion of the plumbing system were greatly enhanced. The diffusive relaxation of olivine zoning provided the timing of storage and migration of a crystal through different environments. For magmas feeding the ancient (〉45 ka) basaltic activ- ity we retrieved transfer histories that are much longer (up to 􏰃3 years) if compared with those cal- culated for the post-GT basalts (1–9 months). The compositional and temporal dataset presented in this study supports the idea that the GT eruption and the subsequent collapse of the volcanic edi- fice could have caused major changes to the internal structural setting of Pantelleria, creating more favorable conditions for the migration of magmas in the upper portions of the plumbing system.
    Description: Published
    Description: egaa05
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
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  • 28
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    The Deep Plumbing System of Ischia: a Physico-chemical Window on the Fluid-saturated and CO2-sustained Neapolitan Volcanism (Southern Italy) (2021)
    Oxford University Press
    Details
    Publication Date: 2021-05-12
    Description: Ischia, a volcanic island located 18 miles SW of Naples (Southern Italy), is a densely populated active caldera that last erupted in AD 1302. Melt inclusions in phenocrysts of the Vateliero and Cava Nocelle shoshonite^latite eruptive products (6th to 4th centuries BC) constrain the structure and nature of the Ischia deep magmatic feeding system.Their geochemical characteristics make Ischia a natural borehole for probing the physico-chemical conditions of magma generation in mantle contaminated by slab-derived fluids or melts, largely dominated by CO2.Volatile concentrations in olivine-hosted melt inclusions require gas^melt equilibria at between 3 and 18 km depth. In agreement with what has already been demonstrated at the other neighboring Neapolitan volcanoes (Procida, Campi Flegrei caldera and Somma^Vesuvius volcanic complex), a major crystallization depth at 8^10 km has been identified.The analyzed melt inclusions provide clear evidence for CO2-dominated gas fluxing and consequent dehydration of magma batches stagnating at crustal discontinuities. Gas fluxing is further supported by selective enrichment in K owing to fluid-transfer during magma differentiation.This takes place under oxidized conditions (Fe3þ /Fe 0·3) that can be fixed by an equimolar proportion of divalent and trivalent iron in the melt if post-entrapment crystallization of the host olivine is discarded.The melt inclusion data, together with data from the literature for other Neapolitan volcanoes, show that magmatism and volcanism in the Neapolitan area, despite differences in composition and eruption dynamics, are closely linked to supercritical CO2-rich fluids. These fluids are produced by devolatilization of subducting terrigenous^pelagic metasediments and infiltrate the overlying mantle wedge, generate magmas and control their ascent up to eruption. Geochemical characteristics of Ischia and the other Neapolitan volcanoes reveal that the extent of fluid or melt contamination of the pre-subduction asthenospheric mantle wedge was similar among these volcanoes. However, differences in the isotopic compositions of the erupted magmas (more enriched in radiogenic Sr at Ischia, Campi Flegrei and Somma^Vesuvius with respect to Procida) and the amount of H2O in the plumbing system of these volcanoes (almost double at Ischia, Campi Flegrei and Somma^Vesuvius than at Procida) reflect the different flow-rates of deep slab-derived fluids or melts through the mantle wedge, which, in turn, control the amount of generated magma.The high bulk permeability of the lithosphere below Ischia, Campi Flegrei and Somma^Vesuvius, determined by the occurrence of intersecting NW^SE and NE^SW regional fault systems, favours fluid ascent and accumulation at crustal levels, with consequent larger magma production and storage than at Procida, located along the NE^SW system.
    Description: Published
    Description: 951-984
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici
    Description: 4V. Processi pre-eruttivi
    Description: 6A. Geochimica per l'ambiente e geologia medica
    Description: JCR Journal
    Keywords: CO2-fluxing ; melt inclusions ; redox state ; trachybasalts
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    A retrospective comparative forecast test on the 1992 Landers sequence (2012)
    American Geophysical Union
    Details
    Publication Date: 2021-06-16
    Description: We perform a retrospective forecast experiment on the 1992 Landers sequence comparing the predictive power of commonly used model frameworks for short‐term earthquake forecasting. We compare a modified short‐term earthquake probability (STEP) model, six realizations of the epidemic‐type aftershock sequence (ETAS) model, and four models that combine Coulomb stress changes calculations and rate‐and‐state theory to generate seismicity rates (CRS models). We perform the experiment under the premise of a controlled environment with predefined conditions for the testing region and data for all modelers. We evaluate the forecasts with likelihood tests to analyze spatial consistency and the total amount of forecasted events versus observed data. We find that (1) 9 of the 11 models perform superior compared to a simple reference model, (2) ETAS models forecast the spatial evolution of seismicity best and perform best in the entire test suite, (3) the modified STEP model matches best the total number of events, (4) CRS models can only compete with empirical statistical models by introducing stochasticity in these models considering uncertainties in the finite‐fault source model, and (5) resolving Coulomb stress changes on 3‐D optimally oriented planes is more adequate for forecasting purposes than using the specified receiver fault concept. We conclude that statistical models perform generally better than the tested physics‐based models and parameter value updates using the occurrence of aftershocks generally improve the predictive power in particular for the purely statistical models in space and time.
    Description: Published
    Description: B05305
    Description: 4.2. TTC - Modelli per la stima della pericolosità sismica a scala nazionale
    Description: JCR Journal
    Description: reserved
    Keywords: earthquake forecast ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
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  • 30
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    The origin of along-rift variations in faulting and magmatism in the Ethiopian Rift (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-06-25
    Description: The geological record at rifts and margins worldwide often reveals considerable along-strike variations in volumes of extruded and intruded igneous rocks. These variations may be the result of asthenospheric heterogeneity, variations in rate, and timing of extension; alternatively, preexisting plate architecture and/or the evolving kinematics of extension during breakup may exert first-order control on magmatism. The Main Ethiopian Rift (MER) in East Africa provides an excellent opportunity to address this dichotomy: it exposes, along strike, several sectors of asynchronous rift development from continental rifting in the south to incipient oceanic spreading in the north. Here we perform studies of volcanic cone density and rift obliquity along strike in the MER. By synthesizing these new data in light of existing geophysical, geochemical, and petrological constraints on magma generation and emplacement, we are able to discriminate between tectonic and mantle geodynamic controls on the geological record of a newly forming magmatic rifted margin. The timing of rift sector development, the three-dimensional focusing of melt, and the ponding of plume material where the rift dramatically narrows each influence igneous intrusion and volcanism along the MER. However, rifting obliquity plays an important role in localizing intrusion into the crust beneath en echelon volcanic segments. Along-strike variations in volumes and types of igneous rocks found at rifted margins thus likely carry information about the development of strain during rifting, as well as the physical state of the convecting mantle at the time of breakup.
    Description: Published
    Description: 467-477
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Variationsinmeltproductioncausedby asynchronous rift sector development • Where the rift narrows, ponding of plume material may enhance melting • Three-dimensional migration of melt along the LAB focuses magma supply ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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  • 31
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    Sulphur behaviour and redox conditions in etnean magmas during magma differentiation and degassing (2021)
    Oxford University Press
    Details
    Publication Date: 2021-06-21
    Description: Sulphur behaviour and variations in redox conditions during magma differentiation and degassing in the Mt Etna (Italy) volcanic system have been explored by integrating the study of olivine-hosted melt inclusions (MIs) with an experimental survey of sulphur solubility in hydrous basaltic magmas. Sulphur solubility experiments were performed at conditions relevant to the Etnean plumbing system (1200 C, 200MPa and oxygen fugacity between NNOþ0 2 and NNOþ1 7, with NNO being the nickel–nickel oxide buffer), and their results confirm the important control of oxygen fugacity (fO2) on S abundance in mafic magmas and on S partitioning between fluid and melt phases (DSfluid/melt). The observed DSfluid/melt value increases from 5164 to 14666 when fO2 decreases from NNOþ1 760 5 to NNOþ0 3. Based on the calculated DSfluid/melt and a careful selection of previously published data, an empirical model is proposed for basaltic magmas to predict the variation of DSfluid/melt values with variations in P (25–300 MPa), T (1030–1200 C) and fO2 (between NNO– 0 8 and NNOþ2 4). Olivine-hosted melt inclusions (Fo89-91) from tephra of the prehistoric (4 ka BP) sub-plinian picritic eruption, named FS (‘Fall Stratified’), have been investigated for their major element compositions, volatile contents and iron speciation (expressed as Fe3þ/PFe ratio). These primitive MIs present S content from 235677 to 34456168 ppm, and oxygen fugacity values, estimated from Fe3þ/PFe ratios, range from NNOþ0 760 2 to NNOþ1 660 2. Iron speciation has also been investigated in more evolved and volatile-poorer Etnean MIs. The only primitive melt inclusion from the Mt Spagnolo eruption (4–15 ka BP) presents a S content of 1515649ppm and an estimated fO2 of NNOþ1 460 1. The more evolved MIs (from 2002–2003, 2006, 2008–2009 and 2013 eruptions) have S content lower than 500 ppm, and their Fe3þ/RFe ratios result in fO2 between NNO– 0 960 1 and NNOþ0 460 1. Redox conditions and S behaviour in Etnean magmas during degassing and fractional crystallization were modelled coupling MELTS code with our empirical DSfluid/melt model. Starting from an FS-type magma composition and upon decrease of T and P, fractional crystallization of olivine, clinopyroxene, spinel and plagioclase causes a significant fO2 decrease. The fO2 reduction, in turn, causes a decrease in sulphur solubility and an increase in DSfluid/melt, promoting S exsolution during magma ascent, which further enhances the reduction of fO2. For the evolved MIs of 2002–2013 eruptions, magma differentiation may therefore have played a crucial role in decreasing redox conditions and favouring efficient S degassing. Differently, during the unusual FS eruption, only limited melt evolution is observed and S exsolution seems to have been triggered by a major pressure decrease accompanied by H2O and CO2 exsolution during fast magmatic ascent.
    Description: Published
    Description: egaa095
    Description: 4V. Processi pre-eruttivi
    Description: JCR Journal
    Keywords: melt inclusions ; sulphur solubility experiments ; XANES ; Mt. Etna ; 04.08. Volcanology
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  • 32
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    Birth of an ocean in the Red Sea: Initial pangs (2012)
    American Geophysical Union
    Details
    Publication Date: 2021-07-14
    Description: We obtained areal variations of crustal thickness, magnetic intensity, and degree of melting of the sub- axial upwelling mantle at Thetis and Nereus Deeps, the two northernmost axial segments of initial oceanic crustal accretion in the Red Sea, where Arabia is separating from Africa. The initial emplacement of oceanic crust occurred at South Thetis and Central Nereus roughly $2.2 and $2 Ma, respectively, and is taking place today in the northern Thetis and southern Nereus tips. Basaltic glasses major and trace element com- position suggests a rift-to-drift transition marked by magmatic activity with typical MORB signature, with no contamination by continental lithosphere, but with slight differences in mantle source composition and/or potential temperature between Thetis and Nereus. Eruption rate, spreading rate, magnetic intensity, crustal thickness and degree of mantle melting were highest at both Thetis and Nereus in the very initial phases of oceanic crust accretion, immediately after continental breakup, probably due to fast mantle upwelling enhanced by an initially strong horizontal thermal gradient. This is consistent with a rift model where the lower continental lithosphere has been replaced by upwelling asthenosphere before continental rupturing, implying depth-dependent extension due to decoupling between the upper and lower lithosphere with man- tle-lithosphere-necking breakup before crustal-necking breakup. Independent along-axis centers of upwell- ing form at the rifting stage just before oceanic crust accretion, with buoyancy-driven convection within a hot, low viscosity asthenosphere. Each initial axial cell taps a different asthenospheric source and serves as nucleus for axial propagation of oceanic accretion, resulting in linear segments of spreading.
    Description: Published
    Description: Q08009
    Description: 2.6. TTC - Laboratorio di gravimetria, magnetismo ed elettromagnetismo in aree attive
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: partially_open
    Keywords: Red Sea ; Gravity and Magnetics ; magma genesis and partial melting ; mantle processes ; transition from continental to oceanic rift ; 04. Solid Earth::04.03. Geodesy::04.03.04. Gravity anomalies ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics
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    Probabilistic Seismic Hazard Analysis at Regional and National Scales: State of the Art and Future Challenges (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-01
    Description: Seismic hazard modeling is a multidisciplinary science that aims to forecast earthquake occurrence and its resultant ground shaking. Such models consist of a probabilistic framework that quantifies uncertainty across a complex system; typically, this includes at least two model components developed from Earth science: seismic source and ground motion models. Although there is no scientific prescription for the forecast length, the most common probabilistic seismic hazard analyses consider forecasting windows of 30 to 50 years, which are typically an engineering demand for building code purposes. These types of analyses are the topic of this review paper. Although the core methods and assumptions of seismic hazard modeling have largely remained unchanged for more than 50 years, we review the most recent initiatives, which face the difficult task of meeting both the increasingly sophisticated demands of society and keeping pace with advances in scientific understanding. A need for more accurate and spatially precise hazard forecasting must be balanced with increased quantification of uncertainty and new challenges such as moving from time‐independent hazard to forecasts that are time dependent and specific to the time period of interest. Meeting these challenges requires the development of science‐driven models, which integrate all information available, the adoption of proper mathematical frameworks to quantify the different types of uncertainties in the hazard model, and the development of a proper testing phase of the model to quantify its consistency and skill. We review the state of the art of the National Seismic Hazard Modeling and how the most innovative approaches try to address future challenges.
    Description: Published
    Description: e2019RG000653
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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  • 34
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    Shallow subduction beneath Italy: Three-dimensional images of the Adriatic-European-Tyrrhenian lithosphere system based on high-quality P wave arrival times (2010)
    American Geophysical Union
    Details
    Publication Date: 2020-10-26
    Description: This paper presents a velocity model of the Italian (central Mediterranean) lithosphere in unprecedented detail. The model is derived by inverting a set of 166,000 Pg and Pn seismic wave arrival times, restricted to the highest-quality data available. The tomographic images reveal the geometry of the subduction-collision system between the European, Adriatic, and Tyrrhenian plates, over a larger volume and with finer resolution than previous studies. We find two arcs of low-Vp anomalies running along the Alps and the Apennines, describing the collision zones of underthrusting continental lithospheres. Our results suggest that in the Apennines, a significant portion of the crust has been subducted below the mountain belt. From the velocity model we can also infer thermal softening of the crustal wedge above the subducting Adriatic plate. In the Tyrrhenian back-arc region, strong and extensive low-Vp anomalies depict upwelling asthenospheric material. The tomographic images also allow us to trace the boundary between the Adriatic and the Tyrrhenian plates at Moho depth, revealing some tears in the Adriatic-Ionian subducting lithosphere. The complex lithospheric structure described by this study is the result of a long evolution; the heterogeneities of continental margins, lithospheric underthrusting, and plate indentation have led to subduction variations, slab tears, and asthenospheric upwelling at the present day. The high-resolution model provided here greatly improves our understanding of the central Mediterranean’s structural puzzle. The results of this study can also shed light on the evolution of other regions experiencing both oceanic and continental subduction.
    Description: Published
    Description: B05305
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: open
    Keywords: lithosphere ; crust ; italy ; plates ; subduction ; europe ; seismicity ; adria ; tyrrhenian ; boundary ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
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  • 35
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    Three-dimensional Moho topography in Italy: New constraints from receiver functions and controlled source seismology (2012)
    American Geophysical Union
    Details
    Publication Date: 2020-10-26
    Description: In complex tectonics regions, seismological, geophysical, and geodynamic modeling require accurate definition of the Moho geometry. Various active and passive seismic experiments performed in the central Mediterranean region revealed local information on the Moho depth, in some cases used to produce interpolated maps. In this paper, we present a new and original map of the 3-D Moho geometry obtained by integrating selected high-quality controlled source seismic and teleseismic receiver function data. The very small cell size makes the retrieved model suitable for detailed regional studies, crustal corrections in teleseismic tomography, advanced 3-D ray tracing in regional earthquake location, and local earthquake tomography. Our results show the geometry of three different Moho interfaces: the European, Adriatic-Ionian, and Tyrrhenian. The three distinct Moho are fashioned following the Alpine and Apennines subduction, collision, and back-arc spreading and show medium- to high-frequency topographic undulations reflecting the complexity of the geodynamic evolution.
    Description: Published
    Description: Q09006
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: Italy; controlled source seismology; crust; receiver function ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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  • 36
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    Importance of earthquake rupture geometry on tsunami modelling: the Calabrian Arc subduction interface (Italy) case study (2020)
    Oxford University Press
    Details
    Publication Date: 2020-10-16
    Description: The behaviour of tsunami waves at any location depends on the local morphology of the coasts, the encountered bathymetric features, and the characteristics of the source. However, the importance of accurately modelling the geometric properties of the causative fault for simulations of seismically induced tsunamis is rarely addressed. In this work, we analyse the effects of using two different geometric models of the subduction interface of the Calabrian Arc (southern Italy, Ionian Sea) onto the simulated tsunamis: a detailed 3-D subduction interface obtained from the interpretation of a dense network of seismic reflection profiles, and a planar interface that roughly approximates the 3-D one. These models can be thought of as representing two end-members of the level of knowledge of fault geometry. We define three hypothetical earthquake ruptures of different magnitudes (Mw 7.5, 8.0, 8.5) on each geometry. The resulting tsunami impact is evaluated at the 50-m isobath in front of coastlines of the central and eastern Mediterranean. Our results show that the source geometry imprint is evident on the tsunami waveforms, as recorded at various distances and positions relative to the source. The absolute differences in maximum and minimum wave amplitudes locally exceed one metre, and the relative differences remain systematically above 20 per cent with peaks over 40 per cent. We also observe that tsunami energy directivity and focusing due to bathymetric waveguides take different paths depending on which fault is used. Although the differences increase with increasing earthquake magnitude, there is no simple rule to anticipate the different effects produced by these end-member models of the earthquake source. Our findings suggest that oversimplified source models may hinder our fundamental understanding of the tsunami impact and great care should be adopted when making simplistic assumptions regarding the appropriateness of the planar fault approximation in tsunami studies. We also remark that the geological and geophysical 3-D fault characterization remains a crucial and unavoidable step in tsunami hazard analyses.
    Description: Published
    Description: 1805–1819
    Description: 3T. Sorgente sismica
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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  • 37
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    Syn-convergent extension observed using the RETREAT GPS network, northern Apennines, Italy (2012)
    American Geophysical Union
    Details
    Publication Date: 2020-11-25
    Description: We present crustal deformation results from a geodetic experiment (Retreating-Trench, Extension, and Accretion Tectonics (RETREAT)) focused on the northern Apennines orogen in Italy. The experiment centers on 33 benchmarks measured with GPS annually or more frequently between 2003 and 2007, supplemented by data from an additional older set of 6 campaign observations from stations in northern Croatia, and 187 continuous GPS stations within and around northern Italy. In an attempt to achieve the best possible estimates for rates and their uncertainties, we estimate and filter common mode signals and noise components using the continuous stations and apply these corrections to the entire data set, including the more temporally limited campaign time series. The filtered coordinate time series data are used to estimate site velocity. We also estimate spatially variable seasonal site motions for stations with sufficient data. The RMS scatter of residual time series are generally near 1 mm and 4 mm, horizontal and vertical, respectively, for continuous and most of the new campaign stations, but scatter is slightly higher for some of the older campaign data. Velocity uncertainties are below 1 mm/yr for all but one of the stations. Maximum rates of site motion within the orogen exceed 3 mm/yr (directed NE) relative to stable Eurasia. This motion is accommodated by extension within the southwestern and central portions of the orogen, and shortening across the foreland thrust belt to the northeast of the range. The data set is consistent with contemporaneous extension and shortening at nearly equal rates. The northern Apennines block moves northeast faster than the Northern Adria microplate. Convergence between the Northern Apennines block and the Northern Adria microplate is accommodated across a narrow zone that coincides with the northeastern Apennines range front. Extension occurs directly above an intact vertically dipping slab inferred by previous authors from seismic tomography. The observed crustal deformation is consistent with a buried dislocation model for crustal faulting, but associations between crustal motion and seismically imaged mantle structure may also provide new insights on mantle dynamics.
    Description: Published
    Description: B04408
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: GPS, northern Apennines, retreat, Italy ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations
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  • 38
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    Neotectonics and long-term seismicity in Europe and the Mediterranean region (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-01-04
    Description: We present a neotectonic model of ongoing lithosphere deformation and a corresponding estimate of long-term shallow seismicity across the Africa-Eurasia plate boundary, including the eastern Atlantic, Mediterranean region, and continental Europe. GPS and stress data are absent or inadequate for the part of the study area covered by water. Thus, we opt for a dynamic model based on the stress-equilibrium equation; this approach allows us to estimate the long-term behavior of the lithosphere (given certain assumptions about its structure and physics) for both land and sea areas. We first update the existing plate model by adding five quasi-rigid plates (the Ionian Sea, Adria, Northern Greece, Central Greece, and Marmara) to constrain the deformation pattern of the study area. We use the most recent datasets to estimate the lithospheric structure. The models are evaluated in comparison with updated datasets of geodetic velocities and the most compressive horizontal principal stress azimuths. We find that the side and basal strengths drive the present-day motion of the Adria and Aegean Sea plates, whereas lithostatic pressure plays a key role in driving Anatolia. These findings provide new insights into the neotectonics of the greater Mediterranean region. Finally, the preferred model is used to estimate long-term shallow seismicity, which we retrospectively test against historical seismicity. As an alternative to reliance on incomplete geologic data or historical seismic catalogs, these neotectonic models help to forecast long-term seismicity, although requiring additional tuning before seismicity rates are used for seismic hazard purposes.
    Description: Published
    Description: 5311–5342
    Description: 1T. Geodinamica e interno della Terra
    Description: 2T. Tettonica attiva
    Description: 3T. Pericolosità sismica e contributo alla definizione del rischio
    Description: JCR Journal
    Description: open
    Keywords: Tectonics ; Earthquake rates ; 04. Solid Earth::04.02. Exploration geophysics::04.02.03. Heat flow ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.04. Geology::04.04.01. Earthquake geology and paleoseismology ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability ; 04. Solid Earth::04.07. Tectonophysics::04.07.01. Continents ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics ; 04. Solid Earth::04.07. Tectonophysics::04.07.04. Plate boundaries, motion, and tectonics ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.07. Tectonophysics::04.07.07. Tectonics
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  • 39
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    Sudden deep gas eruption nearby Rome's airport of Fiumicino (2014)
    American Geophysical Union
    Details
    Publication Date: 2021-03-24
    Description: On 24 August 2013 a sudden gas eruption from the ground occurred in the Tiber river delta, nearby Rome's international airport of Fiumicino. We assessed that this gas, analogous to other minor vents in the area, is dominantly composed of deep, partially mantle-derived CO2, as in the geothermal gas of the surrounding Roman Comagmatic Province. Increased amounts of thermogenic CH4 are likely sourced from Meso-Cenozoic petroleum systems, overlying the deep magmatic fluids. We hypothesize that the intersection of NE-SW and N-S fault systems, which at regional scale controls the location of the Roman volcanic edifices, favors gas uprising through the impermeable Pliocene and deltaic Holocene covers. Pressurized gas may temporarily be stored below these covers or within shallower sandy, permeable layers. The eruption, regardless the triggering cause—natural or man-made, reveals the potential hazard of gas-charged sediments in the delta, even at distances far from the volcanic edifices.
    Description: Published
    Description: 5632–5636
    Description: 2.2. Laboratorio di paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: geothermal gas ; deep CO2 ; Tiber river delta ; thermogenic CH4 ; 04. Solid Earth::04.04. Geology::04.04.09. Structural geology ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
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  • 40
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    On the Heterogeneity of the Earthquake rupture (2021)
    Oxford University Press
    Details
    Publication Date: 2021-04-14
    Description: The scaling of earthquake parameters with seismic moment and its interpretation in terms of self- similarity is still debated in the literature. We address this question by examining a worldwide compilation of corner frequency-based and elastic rebound theory (ERT)-based fault slip, area and stress drop values for earthquakes ranging in magnitude from -0.7 to 7.8. We find that corner frequency estimates of slip (and stress drop) scale differently than those inferred from the ERT approach, where the latter deviates from the generally accepted constant stress drop behavior of so- called self-similar scaling models. We also find that average slips from finite-source models are consistent with corner frequency scaling, whereas peak slip values are more consistent with the ERT scaling. The different scaling of corner frequency- and ERT-based estimates of slip and stress drop with earthquake size is interpreted in terms of heterogeneity of the rupture process. ERT-based estimates of stress drop decrease with seismic moment suggesting a self-affine behavior. Despite the inferred heterogeneity at all scales, we do not observe a clear effect on the Brune stress drop scaling with earthquake size.
    Description: Published
    Description: 1771–1781
    Description: 2T. Deformazione crostale attiva
    Description: JCR Journal
    Keywords: Earthquake dynamics ; Earthquake source observations ; Dynamics and mechanics of faulting ; 04.06. Seismology
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  • 41
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    Relation between subduction megathrust earthquakes, trench sediment thickness and upper plate strain (2012)
    American Geophysical Union
    Details
    Publication Date: 2021-06-16
    Description: Giant earthquake (moment magnitude Mw 〉=8.5) forecasts for subduction zones have been empirically related to both tectonic stresses and geometrical irregularities along the subduction interface. Both of these controls have been suggested as able to tune the ability of rupture to propagate laterally and, in turn, exert an important control on giant earthquake generation. Here we test these hypotheses, and their combined influence, by compiling a dataset of trench fill thickness (a proxy for smoothing of subducting plate relief by sediment input into the subduction channel) and upper plate strain (a proxy for the tectonic stresses applied to the subduction interface) for 44 segments of the global subduction network. We statistically compare relationships between upper plate strain, trench sediment thickness and maximal earthquake magnitude. We find that the combination of both large trench fill (≥1 km) and neutral upper plate strain explains spatial patterns of giant earthquake occurrence to a statistically significant degree. In fact, the concert of these two factors is more highly correlated with giant earthquake occurrence than either factor on its own. Less frequent giant earthquakes of lower magnitude are also possible at subduction zones with thinner trench fill and compressive upper plate strain. Extensional upper plate strain and trench fill 〈 0.5 km appear to be unfavorable conditions, as giant earthquakes have not been observed in these geodynamical environments during the last 111 years.
    Description: Published
    Description: L05304
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: open
    Keywords: subduction zones ; trench sediment thickness ; Upper plate strain ; megathrust earthquakes ; 04. Solid Earth::04.07. Tectonophysics::04.07.06. Subduction related processes
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  • 42
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    Magnetic and seismic reflection study of Lake Cheko, a possible impact crater for the 1908 Tunguska Event (2012)
    American Geophysical Union
    Details
    Publication Date: 2021-06-07
    Description: A major explosion occurred on 30 June 1908 in the Tunguska region of Siberia, causing the destruction of over 2,000 square km of taiga; pressure and seismic waves detected as far as 1,000 km away; bright luminescence in the night skies of Northern Europe and Central Asia; and other unusual phenomena. This “Tunguska Event” is probably related to the impact with the Earth of a cosmic body that exploded about 5-10 km above ground, releasing in the atmosphere 10-15 Mton of energy. Fragments of the impacting body have never been found, and its nature (comet or asteroid) is still a matter of debate. We report here results from a magnetic and seismic-reflection study of a small (~500 m diameter) lake, Lake Cheko, located about 8 km NW of the inferred explosion epicenter, that was proposed to be an impact crater left by a fragment of the Tunguska Cosmic Body. Seismic-reflection and magnetic data revealed a P-wave velocity/magnetic anomaly close to the lake center, about 10 m below the lake floor; this anomaly is compatible with the presence of a buried stony object and supports the impact crater origin for Lake Cheko.
    Description: Published
    Description: Q05008
    Description: 3.4. Geomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Tunguska ; Lake Cheko ; Central Siberia ; Impact cratering ; magnetometry ; seismic reflection ; 04. Solid Earth::04.02. Exploration geophysics::04.02.06. Seismic methods ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies
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  • 43
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    Gas emission strength and evolution of the molar ratio of BrO/SO2 in the plume of Nyiragongo in comparison to Etna (2016)
    American Geophysical Union
    Details
    Publication Date: 2021-06-25
    Description: Airborne and ground-based differential optical absorption spectroscopy observations have been carried out at the volcano Nyiragongo (Democratic Republic of Congo) tomeasure SO2 and bromine monoxide (BrO) in the plume inMarch 2004 and June 2007, respectively. Additionally filter pack andmulticomponent gas analyzer system (Multi-GAS)measurements were carried out in June 2007. Ourmeasurements provide valuable information on the chemical composition of the volcanic plume emitted fromthe lava lake of Nyiragongo. The main interest of this study has been to investigate for the first time the bromine emission flux of Nyiragongo (a rift volcano) and the BrO formation in its volcanic plume. Measurement data and results from a numerical model of the evolution of BrO in Nyiragongo volcanic plume are compared with earlier studies of the volcanic plume of Etna (Italy). Even though the bromine flux from Nyiragongo (2.6 t/d) is slightly greater than that from Etna (1.9 t/d), the BrO/SO2 ratio (maximum 7 × 10 5) is smaller than in the plume of Etna (maximum 2.1 × 10 4). A one-dimensional photochemical model to investigate halogen chemistry in the volcanic plumes of Etna and Nyiragongo was initialized using data from Multi-GAS and filter pack measurements. Model runs showed that the differences in the composition of volcanic volatiles led to a smaller fraction of total bromine being present as BrO in the Nyiragongo plume and to a smaller BrO/SO2 ratio.
    Description: Published
    Description: 277-291
    Description: 4V. Vulcani e ambiente
    Description: JCR Journal
    Description: restricted
    Keywords: Intraplate volcano Nyiragongo is bromine rich although chlorine poor ; BrO/Br in volcanic plumes depends on initial plume composition ; Determination of Nyiragongo chlorine, bromine, sulfur emission strength ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
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  • 44
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    Rotational motions from the 2016, Central Italy seismic sequence, as observed by an underground ring laser gyroscope (2019)
    Oxford University Press
    Details
    Publication Date: 2021-06-21
    Description: We present the analysis of rotational and translational ground motions from earthquakes recorded during October–November 2016, in association with the Central Italy seismic sequence. We use co-located measurements of the vertical ground rotation rate from a large ring laser gyroscope and the three components of ground velocity from a broad-band seismometer. Both instruments are positioned in a deep underground environment, within the Gran Sasso National Laboratories of the Istituto Nazionale di Fisica Nucleare. We collected dozens of events spanning the 3.5–5.9 magnitude range and epicentral distances between 30 and 70 km. This data set constitutes an unprecedented observation of the vertical rotational motions associated with an intense seismic sequence at local distance. Under the plane-wave approximation we process the data set in order to get an experimental estimation of the events backazimuth. Peak values of rotation rate (PRR) and horizontal acceleration (PGA) are markedly correlated, according to a scaling constant which is consistent with previous measurements from different earthquake sequences. We used a prediction model in use for Italy to calculate the expected PGA at the recording site, obtaining consequently predictions for PRR. Within the modelling uncertainties, predicted rotations are consistent with the observed ones, suggesting the possibility of establishing specific attenuation models for ground rotations, like the scaling of peak velocity and peak acceleration in empirical ground-motion prediction relationships. In a second step, after identifying the direction of the incoming wavefield, we extract phase-velocity data using the spectral ratio of the translational and rotational components. This analysis is performed over time windows associated with the P-coda, S-coda and Lg phase. Results are consistent with independent estimates of shear wave velocities in the shallow crust of the Central Apennines
    Description: Published
    Description: 705-715
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
    Keywords: Rotational seismology ; Surface waves and free oscillations ; Wave propagation
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  • 45
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    Experimental study of the interplay between magmatic rift intrusion and flank instability with application to the 2001 Mount Etna eruption (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-07-13
    Description: Mount Etna volcano is subject to transient magmatic intrusions and flank movement. The east flank of the edifice, in particular, is moving eastward and is dissected by the Timpe Fault System. The relationship of this eastward motion with intrusions and tectonic fault motion, however, remains poorly constrained. Here we explore this relationship by using analogue experiments that are designed to simulate magmatic rift intrusion, flank movement, and fault activity before, during, and after a magmatic intrusion episode. Using particle image velocimetry allows for a precise temporal and spatial analysis of the development and activity of fault systems. The results show that the occurrence of rift intrusion episodes has a direct effect on fault activity. In such a situation, fault activitymay occur or may be hindered, depending on the interplay of fault displacement and flank acceleration in response to dike intrusion. Our results demonstrate that a complex interplaymay exist between an active tectonic fault system and magmatically induced flank instability. Episodes of magmatic intrusion change the intensity pattern of horizontal flank displacements andmay hinder or activate associated faults. We further compare our results with the GPS data of the Mount Etna 2001 eruption and intrusion. We find that syneruptive displacement rates at the Timpe Fault System have differed from the preeruptive or posteruptive periods, which shows a good agreement of both the experimental and the GPS data. Therefore, understanding the flank instability and flank stability at Mount Etna requires consideration of both tectonic and magmatic forcing.
    Description: Published
    Description: 5356-5368
    Description: 1V. Storia e struttura dei sistemi vulcanici
    Description: JCR Journal
    Description: restricted
    Keywords: analogue models ; strain ; stress ; eruption ; flank dynamics ; GPS ; faults ; Etna ; 04. Solid Earth::04.03. Geodesy::04.03.08. Theory and Models
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  • 46
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    Assessment of earthquake locations in 3D deterministic velocity models: a case study from the Altotiberina Near Fault Observatory (Italy) (2020)
    American Geophysical Union
    Details
    Publication Date: 2021-07-14
    Description: An edited version of this paper was published by AGU. Copyright (2016) American Geophysical Union.
    Description: The accuracy of earthquake locations and their correspondence with subsurface geology depends strongly on the accuracy of the available seismic velocity model. Most modern methods to construct a velocity model for earthquake location are based on the inversion of passive source seismological data. Another approach is the integration of high-resolution geological and geophysical data to construct deterministic velocity models in which earthquake locations can be directly correlated to the geological structures. Such models have to be kinematically consistent with independent seismological data in order to provide precise hypocenter solutions. We present the Altotiberina (AT) seismic model, a three-dimensional velocity model for the Upper Tiber Valley region (Northern Apennines, Italy), constructed by combining 300 km of seismic reflection profiles, 6 deep boreholes (down to 5 km depth), detailed data from geological surveys and direct measurements of P- and S-wave velocities performed in situ and in laboratory. We assess the robustness of the AT seismic model by locating 11,713 earthquakes with a non-linear, global-search inversion method and comparing the probabilistic hypocenter solutions to those calculated in three previously published velocity models, constructed by inverting passive seismological data only. Our results demonstrate that the AT seismic model is able to provide higher-quality hypocenter locations than the previous velocity models. Earthquake locations are consistent with the subsurface geological structures and show a high degree of spatial correlation with specific lithostratigraphic units, suggesting a lithological control on the seismic activity evolution.
    Description: Published
    Description: 8113-8135
    Description: 4T. Sismicità dell'Italia
    Description: JCR Journal
    Keywords: deterministic velocity model ; earthquakes ; nonlinear hypocenter location ; lithological control on seismicity ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous
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  • 47
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    Intercomparison of stratospheric HNO3measurements over Antarctica: Ground-based millimeter-wave versus UARS/MLS Version 5 retrievals (2020)
    American Geophysical Union
    Details
    Publication Date: 2020-09-21
    Description: [1] We present the first intercomparison between the two most comprehensive records of gas‐phase HNO3 profiles in the Antarctic stratosphere, covering the greater part of 1993 and 1995. We compare measurements by the Stony Brook Ground‐Based Millimeter‐wave Spectrometer (GBMS) at the South Pole with Version 5 HNO3 data from the Microwave Limb Sounder (MLS) aboard the Upper Atmospheric Research Satellite. Trajectory tracing was used to select MLS measurements in the 70°–80°S latitude band that sampled air observed by the GBMS during passage over the Pole. When temperatures were near the HNO3 condensation range, additional screening was performed to select MLS measurements that sampled air parcels within 1.5 K of the temperature they experienced over the Pole. Quantitative comparisons are given at 7 different potential temperature levels spanning the range ∼19–30 km. Agreement between the data sets is quite good between 465 and 655 K (∼20–25 km) during a large fraction of the year. Agreement is best during winter and spring, when seasonally averaged differences are generally within 1 ppbv below ∼25 km. At higher altitudes, and during summer and fall, the agreement becomes worse, and GBMS measurements can exceed MLS values by more than 3 ppbv. We provide evidence that differences occurring in the lower stratosphere during fall are due to lack of colocation between the two data sets during a period of strong poleward gradients in HNO3. Remaining discrepancies between GBMS and MLS V5 HNO3 measurements are thought to be due to instrumental or retrieval biases.
    Description: Published
    Description: id 4809
    Description: 5A. Ricerche polari e paleoclima
    Description: JCR Journal
    Keywords: MLS ; Nitric acid ; polar stratosphere ; 01.01. Atmosphere
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  • 48
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    Discovery of a gliding salt-detached megaslide, Calabria, Ionian Sea, Italy (2013)
    American Geophysical Union
    Details
    Publication Date: 2020-11-26
    Description: Integrating seismic reflection profiles, well logs, and field evidence with GPS velocities from a network installed in Calabria, southern Italy, we have discovered that the Crotone basin is gliding toward the Ionian Sea over a buried viscous salt layer. This previously unknown megaslide (~1000 km2) is characterized by an onshore updip extensional domain and an offshore downdip toe-thrust rim. The GPS velocity from the Crotone station is significantly higher than velocities from other stations in the region and differently oriented. We ascribe at least part of the anomalous GPS velocity from the Crotone station to the seaward motion of the megaslide or part of it. From the GPS velocity and other evidence we obtain a viscosity of the buried salt layer within the known range of rock salt viscosity in nature.
    Description: Published
    Description: 4220-4224
    Description: 3.2. Tettonica attiva
    Description: JCR Journal
    Description: restricted
    Keywords: seismic reflection profiles ; Calabria ; salt ; landslide ; GPS ; 04. Solid Earth::04.04. Geology::04.04.04. Marine geology
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  • 49
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    Impact of appendicularians on detritus and export fluxes: a model approach at Dyfamed site (2012)
    Oxford University Press
    Details
    Publication Date: 2020-11-26
    Description: So far, the role of appendicularians in the biogeochemical cycling of organic matter has been largely overlooked. Appendicularians represent only a fraction of total mesozooplankton biomass, however these ubiquitous zooplankters have very high filtration and growth rates compared to copepods, and produce numerous fecal pellets and filtering houses contributing to export production by aggregating small marine particles. To study their quantitative impact on biogeochemical flux, we have included this group in the biogeochemical flux model, using a recently developed ecophysiological model. One-dimensional annual simulations of the pelagic ecosystem including appendicularians were conducted with realistic surface forcing for the year 2000, using data from the DyFAMed open ocean station. The appendicularian grazing impact was generally low, but appendicularians increased detritus production by 8% and export production by 55% compared to a simulation without appendicularians. Therefore, current biogeochemical models lacking appendicularians probably under, or misestimate the detritus and export production by omitting the pathway from small-sized plankton to fast sinking detritus. Detritus production and export rates are 60% lower than the estimates from mesotrophic sites, showing that appendicularians’ role is lower but still significant in oligotrophic environments. The simulated annual export at 200 m exceeds sediment trap values by 44%, suggesting an intense degradation during the sinking of appendicularian detritus, supported by observations made at other sites. Thus, degradation and grazing of appendicularian detritus need better quantification if we are to accurately assess the role of appendicularia in export flux.
    Description: EU-FP6 project SESAME GOCE-036949
    Description: Published
    Description: 855-872
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: JCR Journal
    Description: reserved
    Keywords: BFM ; zooplankton ; 03. Hydrosphere::03.01. General::03.01.01. Analytical and numerical modeling ; 03. Hydrosphere::03.01. General::03.01.07. Physical and biogeochemical interactions ; 03. Hydrosphere::03.04. Chemical and biological::03.04.01. Biogeochemical cycles ; 03. Hydrosphere::03.04. Chemical and biological::03.04.04. Ecosystems
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  • 50
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    Back to the future: old methods for new estimation and test of the Gutenberg–Richter b-value for catalogues with variable completeness (2020)
    Oxford University Press
    Details
    Publication Date: 2020-11-11
    Description: This article has been accepted for publication in Geophysical Journal International ©: 2021 The Author(s) 2020. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
    Description: In this short paper we show how to use the classical maximum likelihood estimation procedure for the b-value of the Gutenberg–Richter law for catalogues with different levels of completeness. With a simple correction, that is subtracting the relative completeness level to each magnitude, it becomes possible to use the classical approach. Moreover, this correction allows to adopt the testing procedures, initially made for catalogues with a single level of completeness, for catalogues with different levels of completeness too.
    Description: Published
    Description: 337–339
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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  • 51
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    The stress field beneath a quiescent stratovolcano: The case of Mount Vesuvius (2015)
    American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: We have analyzed a focal mechanism data set for Mount Vesuvius, consisting of 197 focal mechanisms of events recorded from 1999 to 2012. Using different approaches and a comparison between observations and numerical models, we have determined the spatial variations in the stress field beneath the volcano. The main results highlight the presence of two seismogenic volumes characterized by markedly different stress patterns. The two volumes are separated by a layer where the seismic strain release shows a significant decrease. Previous studies postulated the existence, at about the same depth, of a ductile layer allowing the spreading of the Mount Vesuvius edifice. We interpreted the difference in the stress pattern within the two volumes as the effect of a mechanical decoupling caused by the aforementioned ductile layer. The stress pattern in the top volume is dominated by a reverse faulting style, which agrees with the hypothesis of a seismicity driven by the spreading process. This agrees also with the persistent character of the seismicity located within this volume. Conversely, the stress field determined for the deep volume is consistent with a background regional field locally perturbed by the effects of the topography and of heterogeneities in the volcanic structure. Since the seismicity of the deep volume shows an intermittent behavior and has shown to be linked to geochemical variations in the fumaroles of the volcano, we hypothesize that it results from the effect of fluid injection episodes, possibly of magmatic origin, perturbing the pore pressure within the hydrothermal system.
    Description: Published
    Description: 1181–1199
    Description: 4T. Fisica dei terremoti e scenari cosismici
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: vesuvius ; stress inversion ; focal mechanisms ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.06. Seismology::04.06.10. Instruments and techniques ; 04. Solid Earth::04.07. Tectonophysics::04.07.05. Stress ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 52
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    Seismic hydraulic fracture migration originated by successive deep magma pulses: The 2011–2013 seismic series associated to the volcanic activity of El Hierro Island (2016)
    American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: In thismanuscript we present a new interpretation of the seismic series that accompanied eruptive activity off the coast of El Hierro, Canary Islands, during 2011–2013. We estimated temporal variations of the Gutenberg-Richter b value throughout the period of analysis, and performed high-precision relocations of the preeruptive and syneruptive seismicity using a realistic 3-D velocity model. Our results suggest that eruptive activity and the accompanying seismicity were caused by repeated injections of magma from the mantle into the lower crust. These magma pulses occurred within a small and well-defined volume resulting in the emplacement of fresh magma along the crust-mantle boundary underneath El Hierro. We analyzed the distribution of earthquake hypocenters in time and space in order to assess seismic diffusivity in the lower crust. Our results suggest that very high earthquake rates underneath El Hierro represent the response of a stable lower crust to stress perturbations with pulsatory character, linked to the injection of magma from the mantle. Magma input from depth caused large stress perturbations to propagate into the lower crust generating energetic seismic swarms. The absence of any preferential alignment in the spatial pattern of seismicity reinforces our hypothesis that stress perturbation and related seismicity, had diffusive character. We conclude that the temporal and spatial evolution of seismicity was neither tracking the path of magma migration nor it defines the boundaries of magma storage volumes such as a midcrustal sill. Our conceptual model considers pulsatorymagma injection fromthe uppermantle and its propagation along the Moho.We suggest, within this framework, that the spatial and temporal distributions of earthquake hypocenters reflect hydraulic fracturing processes associated with stress propagation due to magma movement.
    Description: Published
    Description: 7749–7770
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: b value, relocation, Hydraulic fracturing, Magma influx ; 05. General::05.02. Data dissemination::05.02.99. General or miscellaneous
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  • 53
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    Good practices in PSHA: declustering, b-value estimation, foreshocks and aftershocks inclusion; a case study in Italy (2020)
    Oxford University Press
    Details
    Publication Date: 2020-12-21
    Description: This article has been accepted for publication in Geophysical Journal International. Published by Oxford University Press on behalf of the Royal Astronomical Society.
    Description: The classical procedure of the Probabilistic Seismic Hazard Analysis (PSHA) requires a Poissonian distribution of earthquakes. Seismic catalogs follow a Poisson distribution just after the application of a declustering algorithm that leaves only one earthquake for each seismic sequence (usually the stronger, i.e. the main shock). Removing earthquakes from the seismic catalogs leads to underestimation of the annual rates of the events and consequently associate with low seismic hazard as indicated by several studies. In this study, we aim investigating the performance of two declustering methods on the Italian instrumental catalog and the impact of declustering on estimation of the b-value and on the seismic hazard analysis. To this end, first the spatial variation in the seismicity rate was estimated from the declustered catalogs using the adaptive smoothed seismicity approach, considering small earthquakes (Mw≥3.0). We then corrected the seismicity rates using new approach that allows for counting all events in the complete seismic catalog by simply changing the magnitude frequency distribution. The impact of declustering on seismic hazard analysis is illustrated using PSHA maps in terms of peak ground acceleration (PGA) and spectral acceleration (SA) in 2 s, with 10% and 2% probability of exceedance in 50 years, for Italy. We observed that the hazard calculated from the declustered catalogs was always lower than the hazard computed using the complete catalog. These results are in agreement with previous results obtained in different parts of the world.
    Description: Published
    Description: 1174–1187
    Description: 6T. Studi di pericolosità sismica e da maremoto
    Description: JCR Journal
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  • 54
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    Are there new findings in the search for ULF magnetic precursors to earthquakes? (2016)
    American Geophysical Union
    Details
    Publication Date: 2021-02-10
    Description: Moore (1964) in a letter published in Nature reported disturbances in geomagnetic field data prior to the 27 March 1964 Alaska earthquake. After the publication of this report, many papers have shown magnetic changes preceding earthquakes. However, a causal relationship between preearthquake magnetic changes and impending earthquakes has never been demonstrated. As a consequence, after 50 years, magnetic disturbances in the geomagnetic field are still candidate precursory phenomena. Some researchers consider the investigation of ultra low frequency (ULF: 0.001–10 Hz) magnetic data the correct approach for identifying precursory signatures of earthquakes. Other researchers, instead, have recently reviewed many published ULF magnetic changes that preceded earthquakes and have shown that these are not actual precursors. The recent studies by Currie and Waters (2014) and Han et al. (2014) aim to provide relevant new findings in the search for ULF magnetic precursory signals. However, in order to contribute to science, alleged precursors must be shown to be valid and reproducible by objective testing. Here we will briefly discuss the state of the art in the search for ULF magnetic precursors, paying special attention to the recent findings of Currie and Waters (2014) and Han et al. (2014). We do not see in these two reports significant evidence that may support the observation of precursory signatures of earthquakes in ULF magnetic records.
    Description: Published
    Description: 10289–10304
    Description: 1A. Geomagnetismo e Paleomagnetismo
    Description: JCR Journal
    Description: restricted
    Keywords: Geomagnetic field ; Magnetic anomalies ; Earthquake precursors ; 01. Atmosphere::01.03. Magnetosphere::01.03.03. Magnetospheric physics ; 04. Solid Earth::04.05. Geomagnetism::04.05.04. Magnetic anomalies
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  • 55
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    How a complex basaltic volcanic system works: constraints from integrating seismic, geodetic and petrological data at Mt. Etna volcano during the July-August 2014 eruption (2017)
    American Geophysical Union
    Details
    Publication Date: 2021-04-07
    Description: Integrating geodetic, seismic, and petrological data for a recent eruptive episode at Mount Etna has enabled us to define the history of magma storage and transfer within the multilevel structure of the volcano, providing spatial and temporal constraints for magma movements before the eruption. Geodetic data related to the July–August 2014 activity provide evidence of a magma reservoir at ~4 km below sea level. This reservoir pressurized from late March 2014 and fed magmas that were then erupted from vents on the lower eastern flank of North-East Crater (NEC) and at New South-East Crater (NSEC) summit crater during the July eruptive activity. Magma drainage caused its depressurization since mid-July. Textural and microanalytical data obtained from plagioclase crystals indicate similar disequilibrium textures and compositions at the cores in lavas erupted at the base of NEC and NSEC, suggesting comparable deep histories of evolution and ascent. Conversely, the compositional differences observed at the crystal rims have been associated to distinct degassing styles during storage in a shallow magma reservoir. Seismic data have constrained depth for a shallow part of the plumbing system at 1–2 km above sea level. Timescales of magma storage and transfer have also been calculated through diffusion modeling of zoning in olivine crystals of the two systems. Our data reveal a common deep history of magmas from the two systems, which is consistent with a recharging phase by more mafic magma between late March and early June 2014. Later, the magma continued its crystallization under distinct chemical and physical conditions at shallower levels.
    Description: The petrological part of this study was supported by the FIR 2014 research grant to Marco Viccaro from the University of Catania (Italy), grant number 2F119B, title of the project “Dynamics of evolution, ascent and emplacement of basic magmas: case-studies from eruptive manifestations of Eastern Sicily”.
    Description: Published
    Description: 5659–5678
    Description: 2V. Dinamiche di unrest e scenari pre-eruttivi
    Description: 3V. Dinamiche e scenari eruttivi
    Description: JCR Journal
    Description: restricted
    Keywords: Petrology ; eruption ; GPS ; volcano seismology ; Etna ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.07. Satellite geodesy ; 04. Solid Earth::04.04. Geology::04.04.07. Rock geochemistry ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
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  • 56
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    Crustal and uppermost mantle shear wave velocity structure beneath the Middle East from surface wave tomography (2021)
    Oxford University Press
    Details
    Publication Date: 2021-05-12
    Description: We have constructed a 3-D shear wave velocity (Vs) model for the crust and uppermost mantle beneath the Middle East using Rayleigh wave records obtained from ambient-noise cross-correlations and regional earthquakes. We combined one decade of data collected from 852 permanent and temporary broad-band stations in the region to calculate group-velocity dispersion curves. A compilation of 〉54 000 ray paths provides reliable group-velocity measurements for periods between 2 and 150 s. Path-averaged group velocities calculated at different periods were inverted for 2-D group-velocity maps. To overcome the problem of heterogeneous ray coverage, we used an adaptive grid parametrization for the group-velocity tomographic inversion. We then sample the period-dependent group-velocity field at each cell of a predefined grid to generate 1-D group-velocity dispersion curves, which are subsequently inverted for 1-D Vs models beneath each cell and combined to approximate the 3-D Vs structure of the area. The Vs model shows low velocities at shallow depths (5–10 km) beneath the Mesopotamian foredeep, South Caspian Basin, eastern Mediterranean and the Black Sea, in coincidence with deep sedimentary basins. Shallow high-velocity anomalies are observed in regions such as the Arabian Shield, Anatolian Plateau and Central Iran, which are dominated by widespread magmatic exposures. In the 10–20 km depth range, we find evidence for a band of high velocities (〉4.0 km s–1) along the southern Red Sea and Arabian Shield, indicating the presence of upper mantle rocks. Our 3-D velocity model exhibits high velocities in the depth range of 30–50 km beneath western Arabia, eastern Mediterranean, Central Iranian Block, South Caspian Basin and the Black Sea, possibly indicating a relatively thin crust. In contrast, the Zagros mountain range, the Sanandaj-Sirjan metamorphic zone in western central Iran, the easternmost Anatolian plateau and Lesser Caucasus are characterized by low velocities at these depths. Some of these anomalies may be related to thick crustal roots that support the high topography of these regions. In the upper mantle depth range, high-velocity anomalies are obtained beneath the Arabian Platform, southern Zagros, Persian Gulf and the eastern Mediterranean, in contrast to low velocities beneath the Red Sea, Arabian Shield, Afar depression, eastern Turkey and Lut Block in eastern Iran. Our Vs model may be used as a new reference crustal model for the Middle East in a broad range of future studies.
    Description: Published
    Description: 1349-1365
    Description: 1T. Struttura della Terra
    Description: JCR Journal
    Keywords: 04.01. Earth Interior ; 04.06. Seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Periodic volcanic degassing behavior: The Mount Etna example (2013)
    American Geophysical Union
    Details
    Publication Date: 2021-06-25
    Description: In contrast to the seismic and infrasonic energy released from quiescent and erupting volcanoes, which have long been known to manifest episodes of highly periodic behavior, the spectral properties of volcanic gas flux time series remain poorly constrained, due to a previous lack of hightemporal resolution gas-sensing techniques. Here we report on SO2 flux measurements, performed on Mount Etna with a novel UV imaging technique of unprecedented sampling frequency (0.5 Hz), which reveal, for the first time, a rapid periodic structure in degassing from this target. These gas flux modulations have considerable temporal variability in their characteristics and involve two period bands: 40–250 and 500–1200 s. A notable correlation between gas flux fluctuations in the latter band and contemporaneous seismic root-mean-square values suggests that this degassing behavior may be generated by periodic bursting of rising gas bubble trains at the magma-air interface.
    Description: Published
    Description: 4818–4822
    Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive
    Description: JCR Journal
    Description: restricted
    Keywords: SO2 flux ; UV camera ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
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    Discrimination between induced, triggered and natural earthquakes close to hydrocarbon reservoirs: A probabilistic approach based on the modeling of depletion-induced stress changes and seismological source parameters. (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-06-16
    Description: Earthquakes occurring close to hydrocarbon fields under production are often under critical view of being induced or triggered. However, clear and testable rules to discriminate the different events have rarely been developed and tested. The unresolved scientific problem may lead to lengthy public disputes with unpredictable impact on the local acceptance of the exploitation and field operations. We propose a quantitative approach to discriminate induced, triggered and natural earthquakes, which is based on testable input parameters. Maxima of occurrence probabilities are compared for the cases under question, and a single probability of being triggered or induced is reported. The uncertainties of earthquake location and other input parameters are considered in terms of the integration over probability density functions (pdf). The probability that events have been human-triggered/induced is derived from the modeling of Coulomb stress changes and a rate and state dependent seismicity model. In our case a 3D boundary element method has been adapted for the nuclei of strain approach to estimate the stress changes outside the reservoir, which are related to pore pressure changes in the field formation. The predicted rate of natural earthquakes is either derived from the background seismicity or, in case of rare events, from an estimate of the tectonic stress rate. Instrumentally derived, seismological information on the event location, source mechanism and the size of the rupture plane is of advantage for the method. If the rupture plane has been estimated, the discrimination between induced or only triggered events is theoretically possible if probability functions are convolved with a rupture fault filter. We apply the approach to three recent main-shock events: (1) the Mw 4.3 Ekofisk 2001, North Sea earthquake close to the Ekofisk oil field, the 2004 Mw 4.4 Rotenburg, Northern Germany earthquake in the vicinity of the Söhlingen gas field, and the Mw 6.1 Emilia 2012, Northern Italy earthquake in the vicinity of a hydrocarbon reservoir. The three test cases cover the complete range of possible causes: clearly “human-induced”, “not even human-triggered” and a third case in-between both extremes.
    Description: Published
    Description: 2491–2509
    Description: 6T. Sismicità indotta e caratterizzazione sismica dei sistemi naturali
    Description: JCR Journal
    Description: restricted
    Keywords: Induced seismicity ; probabilistic discrimination ; hydrocarbon field ; triggered earthquake ; seismic hazard ; earthquake ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability
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    Gas emissions from five volcanoes in northern Chile and implications for the volatiles budget of the Central Volcanic Zone (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-06-16
    Description: This study performed the first assessment of the volcanic gas output from the Central Volcanic Zone (CVZ) of northern Chile. We present the fluxes and compositions of volcanic gases (H2O, CO2, H2, HCl, HF, and HBr) from five of the most actively degassing volcanoes in this region—Láscar, Lastarria, Putana, Ollagüe, and San Pedro—obtained during field campaigns in 2012 and 2013. The inferred gas plume compositions for Láscar and Lastarria (CO2/Stot = 0.9–2.2; Stot/HCl = 1.4–3.4) are similar to those obtained in the Southern Volcanic Zone of Chile, suggesting uniform magmatic gas fingerprint throughout the Chilean arc. Combining these compositions with our own UV spectroscopy measurements of the SO2 output (summing to ~1800 t d 1 for the CVZ), we calculate a cumulative CO2 output of 1743–1988 t d 1 and a total volatiles output of 〉20,200 t d 1. 1.
    Description: Published
    Description: 4961-4969
    Description: 5V. Sorveglianza vulcanica ed emergenze
    Description: JCR Journal
    Description: restricted
    Keywords: Gas output from the Central Volcanic Zone ; 04. Solid Earth::04.08. Volcanology::04.08.01. Gases
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    Mercury Degassing on Africa-Adriatic Tectonic Plate Margin (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-06-25
    Description: Beside anthropogenic influences, mercury in the environment can also be of natural origin. Among geologic sources, volcanic activity has been of main interest so far. Modern estimations of global natural emissions are between 2000 and 5200 tonnes per year. However, these estimates are very uncertain, thus more detailed and systematic research on natural sources of mercury is necessary. Tectonic activity is connected to certain phenomena such as degassing of Hg and other gases from active faults, geothermal activity, volcanoes, etc., especially on tectonic plate margins. Elemental mercury concentrations in air, soil gases and fluxes, as well as its speciation, in connection to tectonic activity, were studied in different environments such are karst cave (Postojna Cave), active volcano areas (Mt. Etna, Italy), and active tectonic areas in the Mediterranean Basin on Africa-Adriatic tectonic plate margin. Postojna Cave is characterized by elevated Hg (up to 150 ng m-3) air concentrations at certain areas in vicinity of active faults; however the concentrations showed also strong seasonal variations. Mt. Etna on Sicily is the largest and most active Mediterranean volcano. Concentrations of mercury in air in the vicinity of the volcano are relatively high (between 4 and 30 ng m-3) and rise towards the summit crater (65 to 130 ng m-3). Concentrations in sulphatare and fumaroles gases on the summit of the volcano can reach very high values (even up to 60 μg m-3). The Mediterranean Basin is characterized by strong tectonic activity as a consequence of subduction of African plate under the Eurasian plate. A possible source of DGM (dissolved gaseous mercury in sea water) in deeper and bottom waters could be intensive tectonic activity of the seafloor, since higher concentrations and portions of DGM were found near the bottom at locations with strong tectonic activity (Alboran Sea, Strait of Sicily, Tyrrhenian Sea, Ionian Sea). Distribution of different mercury species in sediment and water of the Mediterranean Sea showed that the main source of mercury is geotectonic activity and its accompanying phenomena.
    Description: Published
    Description: San Francisco
    Description: 6A. Monitoraggio ambientale, sicurezza e territorio
    Description: restricted
    Keywords: Mercury ; 04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
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    The protracted development of focused magmatic intrusion during continental rifting (2015)
    American Geophysical Union
    Details
    Publication Date: 2021-06-25
    Description: The transition from mechanical thinning toward focused magmatic intrusion during continental rifting is poorly constrained; the tectonically active Main Ethiopian Rift (MER) provides an ideal study locale to address this issue. The presence of linear magmatic-tectonic belts in the relatively immature central MER may indicate that the transition from mechanical to magmatic rifting is more spatially distributed and temporally protracted than has previously been assumed. Here we examine lava geochemistry and vent distribution of a Pliocene-Quaternary linear magmatic chain along the western margin of the central MER—the Akaki Magmatic Zone. Our results show limited variability in parental magma that evolve in a complex polybaric fractionation system that has not changed significantly over the past 3 Ma. Our results suggest the following: (1) channeling of plume material and the localization of shear- or topography-induced porosity modulates melt intrusion into the continental lithosphere. (2) Pre-existing lithospheric structures may act as catalysts for intrusion of magmas into the lithospheric mantle. (3) The midcrustal to upper crustal strain regime dictates the surface orientation of volcanic vents. Therefore, although linear magmatic belts like those in the central MER may young progressively toward the rift axis and superficially resemble oceanic style magmatism, they actually represent prebreakup magmatism on continental crust. The oldest linear magmatic belts observed seismically and magnetically at the edge of the ocean basins thus may not, as is often assumed, actually mark the onset of seafloor spreading.
    Description: Published
    Description: 875–897
    Description: 1T. Geodinamica e interno della Terra
    Description: JCR Journal
    Description: restricted
    Keywords: Precambrian lineaments control off-axis melt • Magmatic extension in Ethiopian rift is not ocean like • Magmatic belts at basins margins may not be seafloor spreading ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
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    Atlantic Water advection versus sea-ice advances in the eastern Fram Strait during the last 9 ka: Multiproxy evidence for a two-phase Holocene (2013)
    American Geophysical Union
    In:  EPIC3Paleoceanography, American Geophysical Union, 28(2), pp. 283-295, ISSN: 1944-9186
    Details
    Publication Date: 2019-07-16
    Description: A sediment core from the West Spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last ~9 ka in the eastern Fram Strait (FS). Our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern FS occurred stepwise, in response to the postglacial sea-level rise and the related onset of modern sea-ice production on the shallow Siberian shelves. The late Early and Mid-Holocene interval (9 to 5 ka) was generally characterized by relatively unstable conditions. High abundance of the subpolar planktic foraminifer species Turborotalita quinqueloba implies strong intensity of Atlantic Water (AW) inflow with high productivity and/or high AW temperatures, resulting in a strong heat flux to the Arctic. A series of short-lived cooling events (8.2, 6.9, and 6.1 ka) occurred superimposed on the warm late Early to Mid-Holocene conditions. Our proxy data imply that simultaneous to the complete postglacial flooding of Arctic shallow shelves and the initiation of modern sea-ice production, strong advance of polar waters initiated modern oceanographic conditions in the eastern FS at ~5.2 ka. The Late Holocene was marked by the dominance of the polar planktic foraminifer species Neogloboquadrina pachyderma, a significant expansion of sea ice/icebergs, and strong stratification of the water column. Although planktic foraminiferal assemblages as well as sea subsurface temperatures suggest a return of slightly strengthened advection of subsurface AW after 3 ka, a relatively stable cold-water layer prevailed at the sea surface, and the study site was probably located within the seasonally fluctuating marginal ice zone during the Neoglacial period.
    Repository Name: EPIC Alfred Wegener Institut
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    Marine ice sheets of Pleistocene age on the East Siberian Continental Margin (2013)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, 2013-12-08-2013-12-13American Geophysical Union
    Details
    Publication Date: 2016-02-02
    Description: Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present results of the RV „Polarstern“ cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA02B (2012), which investigated an area between the Chukchi Borderland and the East Siberian Sea between 165°W and 170°E. At the southern end of the Mendeleev Ridge, close to the Chukchi and East Siberian shelves, evidence is found for the existence of Pleistocene ice sheets/ice shelves, which have grounded several times in up to 1200 m present water depth. We found mega-scale glacial lineations associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale erosion, accentuated by a conspicuous truncation of pre-glacial strata typically capped with mostly thin layers of diamicton draped by pelagic sediments. Our tentative age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3. The oldest and deepest event predates MIS 6. According to our results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf. They were possibly linked to previously suggested ice sheets on the Chukchi Borderland and the New Siberian Islands. We propose that the ice sheets extended northward as thick ice shelves, which grounded on the Mendeleev Ridge to an area up to 78°N within MIS 5 and/or earlier. These results have important implication for the former distribution of thick ice masses in the Arctic Ocean during the Pleistocene. They are relevant for global sea-level variations, albedo, ocean-atmosphere heat exchange, freshwater export from the Arctic Ocean at glacial terminations and the formation of submarine permafrost. The existence of km-thick Pleistocene ice sheets in the western Arctic Ocean during glacial times predating that of the Last Glacial Maximum (LGM) also implies significantly different atmospheric circulation patterns, in particular availability and distribution of moisture during pre-LGM glaciations.
    Repository Name: EPIC Alfred Wegener Institut
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    Linking Sea Ice Physical Properties with Under-Ice and In-Ice Ecosystems (2012)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, San Francisco, Calif., USA, 2012-12-03-2012-12-07American Geophysical Union
    Details
    Publication Date: 2019-07-17
    Description: Impacts of climate change have been most pronounced in Polar Regions. Most alarming is the accelerating decline in Arctic sea ice cover. The changing ice cover has implications for sea ice-associated ecosystems because they rely largely on carbon produced by ice-associated algae. In order to fully understand these ecosystems and to be able to accurately represent them in models there is a need to understand both the physical and biological components of the system. The study presented here is part of AWI’s research group Iceflux which takes an interdisciplinary approach to quantify the trophic carbon flux within sea ice associated ecosystems in the Arctic and Antarctic. Here we will present preliminary results from the ARK XXVII/3 Polarstern Cruise. Biological samples were acquired from the under-ice surface waters using the Surface and Under-Ice Trawl (SUIT) and from within the sea ice by extracting ice cores. To characterize the biophysical properties of the sea ice and under-ice environments several sensors were mounted on the SUIT including: spectral radiometer, ADCP, CTD, fluorometer, altimeter (distance to ice bottom) and video camera. Observations include ice thickness, biological diversity, biomass, light transmission, under-ice water properties and chlorophyll a content (in- and under-ice). Preliminary results will provide a description of the local- to meso-scale spatial variability of biological abundance in and under the ice and the relationship with different sea ice characteristics. During the cruise testing of sensors and equipment will be conducted in order to prepare for the deployment of two Autonomous Bio-Physical Sea Ice Observatories (ABiPSO) stations in the Weddell Sea during the ANT XXIX/6 cruise June 2013. A description of the ABiPSO system and testing of the sensors will be presented highlighting the objectives, challenges and lessons learned.
    Repository Name: EPIC Alfred Wegener Institut
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    Methane and nitrous oxide distributions across the North American Arctic Ocean during summer 2015 (2017)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical research: Ocean, American Geophysical Union, 122, pp. 1-18
    Details
    Publication Date: 2017-11-12
    Description: We collected Arctic Ocean water column samples for methane (CH4) and nitrous oxide (N2O) analysis on three separate cruises in the summer and fall of 2015, covering a ~10,000 km transect from the Bering Sea to Baffin Bay. This provided a three-dimensional view of CH4 and N2O distributions across contrasting hydrographic environments, from the oligotrophic waters of the deep Canada Basin and Baffin Bay, to the productive shelves of the Bering and Chukchi Seas. Percent saturation relative to atmospheric equilibrium ranged from 30-800% for CH4 and 75-145% for N2O, with the highest concentrations of both gases occurring in the northern Chukchi Sea. Nitrogen cycling in the shelf sediments of the Bering and Chukchi Seas likely constituted the major source of N2O to the water column, and the resulting high N2O concentrations were transported across the Arctic Ocean in eastward-flowing water masses. Methane concentrations were more spatially heterogeneous, reflecting a variety of localized inputs, including likely sources from sedimentary methanogenesis and sea ice processes. Unlike N2O, CH4 was rapidly consumed through microbial oxidation in the water column, as shown by the 13C enrichment of CH4 with decreasing concentrations. For both CH4 and N2O, sea-air fluxes were close to neutral, indicating that our sampling region was neither a major source nor sink of these gases. Our results provide insight into the factors controlling the distribution of CH4 and N2O in the North American Arctic Ocean, and an important baseline data set against which future changes can be assessed.
    Repository Name: EPIC Alfred Wegener Institut
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    Paleobathymetric grids of the Cenozoic Southern Ocean - opening the door towards improved reconstructions of the Southern Ocean (2017)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2018, New Orleans, USA, 2017-12-10-2017-12-16New Orleans, USA, American Geophysical Union
    Details
    Publication Date: 2018-01-11
    Repository Name: EPIC Alfred Wegener Institut
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    Moderately warm upper mantle beneath the Tristan da Cunha Hotspot, from Rayleigh-wave dispersion and petrological modeling (2018)
    American Geophysical Union
    In:  EPIC3Geochemistry, Geophysics, Geosystems, American Geophysical Union, (19), pp. 1412-1428
    Details
    Publication Date: 2018-07-15
    Description: Understanding the enigmatic intraplate volcanism in the Tristan da Cunha region requires knowledge of the temperature of the lithosphere and asthenosphere beneath it. We measured phasevelocity curves of Rayleigh waves using cross-correlation of teleseismic seismograms from an array of ocean-bottom seismometers around Tristan, constrained a region-average, shear-velocity structure, and inferred the temperature of the lithosphere and asthenosphere beneath the hotspot. The ocean-bottom data set presented some challenges, which required data-processing and measurement approaches different from those tuned for land-based arrays of stations. Having derived a robust, phase-velocity curve for the Tristan area, we inverted it for a shear wave velocity profile using a probabilistic (Markov chain Monte Carlo) approach. The model shows a pronounced low-velocity anomaly from 70 to at least 120 km depth. VS in the low velocity zone is 4.1–4.2 km/s, not as low as reported for Hawaii (�4.0 km/s), which probably indicates a less pronounced thermal anomaly and, possibly, less partial melting. Petrological modeling shows that the seismic and bathymetry data are consistent with a moderately hot mantle (mantle potential temperature of 1,410–1,4308C, an excess of about 50–1208C compared to the global average) and a melt fraction smaller than 1%. Both purely seismic inversions and petrological modeling indicate a lithospheric thickness of 65–70 km, consistent with recent estimates from receiver functions. The presence of warmer-than-average asthenosphere beneath Tristan is consistent with a hot upwelling (plume) from the deep mantle. However, the excess temperature we determine is smaller than that reported for some other major hotspots, in particular Hawaii.
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    Chronostratigraphy and paleoenvironmental change in the Makarov Basin of the western Arctic Ocean during the last 1 Ma (2017)
    American Geophysical Union
    In:  EPIC3AGU, Fall Meeting 2017, Poster PP51B-1067, New Orleans, 2017-12-15-2017-12-15New Orleans, USA, American Geophysical Union
    Details
    Publication Date: 2019-05-12
    Description: Establishing an accurate chronostratigraphy is essential in reconstructing paleoenvironmental changes in the Arctic Ocean. This requisition, however, has been impeded by the lack of biogenic remnants such as calcareous and siliceous microfossils, as well as alteration of paleomagnetic properties by post-depositional processes. Consequently, foundation of chronostratigraphy in the Arctic Ocean has been mostly relying on stratigraphic correlations. This study examines lithological features and physical properties of sediments of gravity core ARA03B-41GC02 collected in the Makarov Basin and correlates with previously studied cores from the western Arctic Ocean, in order to establish an age model that could eventually facilitate a precise reconstruction of paleoenvironmental changes in the western Arctic Ocean. Age control in the uppermost part was determined by AMS 14C dating of planktonic foraminifera and inter-core correlation was conducted in the upper ca. 3.8 m of the core which corresponded to MIS 15. Age constraints older than MIS 15 were treated using cyclostratigraphic model based on Mn-δ18O stack comparison, assuming that brown and high Mn concentration layers represent generally interglacial or interstadial periods. Based on our result, the core bottom corresponds to MIS 28 with an average sedimentation rate of ca. 0.5 cm/ky. The first appearance of detrital carbonate, planktonic foraminifera, and benthic foraminifera occurred during MIS 16, 11, and 7, respectively. MIS 16 is known as the coldest glacial period when δ18O of the LR04 stack first becomes heavier than 5‰; the occurrence of detrital carbonate likely transported from the Canadian Arctic indicates the initial buildup of the large ice sheets in the North America during this time. Since MIS 11 which is known as the warmest interglacial period during the late Pleistocene in the Northern Hemisphere, the appearance of planktonic foraminifera represents the warmer condition during interglacial periods in the western central Arctic Ocean. Additional geochemical and mineralogical proxies need to be conducted for better understanding of depositional environments and sediment provenance as well as transport pathways.
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    Tropical Rains Controlling Deposition of Saharan Dust Across the North Atlantic Ocean (2020)
    American Geophysical Union
    In:  EPIC3Geophysical Research Letters, American Geophysical Union, 47(5), ISSN: 0094-8276
    Details
    Publication Date: 2020-05-13
    Description: Mineral dust plays an important role in the atmospheric radiation budget as well as in the ocean carbon cycle through fertilization and by ballasting of settling organic matter. However, observational records of open‐ocean dust deposition are sparse. Here, we present the spatial and temporal evolution of Saharan dust deposition over 2 years from marine sediment traps across the North Atlantic, directly below the core of the Saharan dust plume, with highest dust fluxes observed in summer. We combined the observed deposition fluxes with model simulations and satellite observations and argue that dust deposition in the Atlantic is predominantly controlled by summer rains. The dominant depositional pathway changes from wet deposition in summer to dry deposition in winter. Wet deposition has previously been suggested to increase the release of dust‐derived nutrients and their bioavailability, which may be a key contributor to surface‐ocean productivity in remote and oligotrophic parts of the oceans.
    Repository Name: EPIC Alfred Wegener Institut
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    Arctic Continental Margin Sediments as Possible Fe and Mn Sources to Seawater as Sea Ice Retreats: Insights From the Eurasian Margin (2020)
    American Geophysical Union
    In:  EPIC3Global Biogeochemical Cycles, American Geophysical Union, 34(8), ISSN: 0886-6236
    Details
    Publication Date: 2020-09-02
    Repository Name: EPIC Alfred Wegener Institut
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    Ice flow and the conditions of the ice-bed interface at the onset of the Northeast Greenland Ice Stream (2020)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2020 - Online Everywhere, Online, 2020-12-01-2020-12-17American Geophysical Union
    Details
    Publication Date: 2020-12-15
    Description: The Northeast Greenland Ice Stream (NEGIS) is an important dynamic component contributing to the total mass balance of the Greenland ice sheet, as it reaches up to the central divide and drains 12% of the ice sheet. The ice stream geometry and surface velocities in the onset region of the NEGIS are not yet sufficiently well reproduced by ice sheet models. We present an assessment of the basal conditions of the onset region in a systematic analysis of airborne ultra-wideband radar data. Our data yield a new detailed model of ice-thickness distribution and basal topography in the upstream part of the ice stream. We observe a change from a smooth to a rougher bed where the ice stream widens from 10 to 60 km, and a distinct roughness anisotropy, indicating a preferred orientation of subglacial structures. The observation of off-nadir reflections that are symmetrical to the bed reflection in the radargrams suggests that these structures are elongated subglacial landforms, which in turn indicate potential streamlining of the bed. Together with basal water routing pathways, our observations hint to two different zones in this part of the NEGIS: an accelerating and smooth upstream region, which is collecting water, with reduced basal traction, and in the further downstream part, where the ice stream is slowing down and is widening, with a distribution of basal water towards the shear margins. Our findings support the hypothesis that the NEGIS is strongly interconnected to the subglacial water system in its onset region, but also to the subglacial substrate and morphology.
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    Sea Ice Targeted Geoengineering Can Delay Arctic Sea Ice Decline but not Global Warming (2019)
    American Geophysical Union
    In:  EPIC3Earth's Future, American Geophysical Union, 7(12), pp. 1296-1306, ISSN: 2328-4277
    Details
    Publication Date: 2021-02-15
    Description: To counteract global warming, a geoengineering approach that aims at intervening in the Arctic ice‐albedo feedback has been proposed. A large number of wind‐driven pumps shall spread seawater on the surface in winter to enhance ice growth, allowing more ice to survive the summer melt. We test this idea with a coupled climate model by modifying the surface exchange processes such that the physical effect of the pumps is simulated. Based on experiments with RCP 8.5 scenario forcing, we find that it is possible to keep the late‐summer sea ice cover at the current extent for the next ∼60 years. The increased ice extent is accompanied by significant Arctic late‐summer cooling by ∼1.3 K on average north of the polar circle (2021–2060). However, this cooling is not conveyed to lower latitudes. Moreover, the Arctic experiences substantial winter warming in regions with active pumps. The global annual‐mean near‐surface air temperature is reduced by only 0.02 K (2021–2060). Our results cast doubt on the potential of sea ice targeted geoengineering to mitigate climate change.
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    Simulated Thermohaline Fingerprints in Response to Different Greenland‐Scotland Ridge and Fram Strait Subsidence Histories (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-16
    Description: Changes in ocean gateway configuration can induce basin‐scale rearrangements in ocean current characteristics. However, there is large uncertainty in the relative timing of the Oligocene/Miocene subsidence histories of the Greenland‐Scotland Ridge (GSR) and the Fram Strait (FS). By using a climate model, we investigate the temperature and salinity changes in response to the subsidence of these two key ocean gateways during early to middle Miocene. For a singular subsidence of the GSR, we detect warming and a salinity increase in the Nordic Seas and the Arctic Ocean. As convection sites shift to the north of Iceland, North Atlantic Deep Water (NADW) is formed at cooler temperatures. The associated deep ocean cooling and upwelling of deep waters to the Southern Ocean surface can cause a cooling in the southern high latitudes. These characteristic responses to the GSR deepening are independent of the FS being shallow or deep. An isolated subsidence of the FS gateway for a deep GSR shows less pronounced warming and salinity increase in the Nordic Seas. Arctic temperatures remain unaltered, but a stronger salinity increase is detected, which further increases the density of NADW. The increase in salinity enhances the contribution of NADW to the abyssal ocean at the expense of the colder southern source water component. These relative changes largely counteract each other and cause a negligible warming in the upwelling regions of the Southern Ocean.
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    Reduced winter off-road tundra travel under climate change (2019)
    American Geophysical Union
    In:  EPIC3AGU Fall meeting, San Francisco, CA, 2019-12-09-2019-12-13USA, American Geophysical Union
    Details
    Publication Date: 2019-12-17
    Description: During the last decade the Arctic has experienced increasing human development while many native communities continue to live a subsistence lifestyle. Off-road winter tundra travel for resource exploration is most cost effective and least environmentally damaging during winter when the tundra is frozen and snow covered. Climate warming, which is occurring at an amplified rate in the Arctic, likely changes the period when access to the off-road tundra travel is possible. There currently exists, however, large uncertainty as to how climate change will impact the low-cost winter travel access across the tundra. Here we defined safe tundra access when soil temperatures are below a soil type dependent freezing temperature and snow cover is at least 20 cm. Our analysis is based on the simulated soil temperatures and snow depths of Land Surface Models (LSMs) contributing to “The Inter-Sectoral Impact Model Intercomparison Project” (ISIMIP). ISIMIP simulations are based on a common protocol, the same input data, the same spatial (0.5°) and temporal resolution (daily modeling output), and span over the period 1861-2100. The LSMs are forced by four different bias-corrected global circulation models (IPSL-CM5A-LR, GFDL-ESM2M, MIROC5, HadGEM2-ES) and three different future conditions (represented via representative concentration pathways (RCP) 2.6, 6.0, 8.5). The simulation results of our model ensemble (60 model combinations) show consistent permafrost warming and changing snow cover patterns at 60°N. Annual off-road tundra travel is considerably reduced (〉50%) under future climate change scenarios, especially under the RCP8.5. The main reduction can be observed in the spring and autumn (〉30%). The results of the multi-model ensemble differ in magnitude, however, their overall trend is consistent. Our results suggest a high vulnerability and substantial changes to the (subsistence) livelihoods of native communities and increasing costs for off-road resource exploration.
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    Genomic Observatories Network: socio-technical perspectives on the path to long-term multi-omic observation (2018)
    American Geophysical Union
    In:  EPIC3American Geophysical Union Fall Meeting, Washington D.C., USA, 2018-12-10-2018-12-14American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Description: Four years after the Genomic Observatories Network was formally established as a collaboration between the Group on Earth Observations Biodiversity Observation Network and the Genomic Standards Consortium, we review the development of the network. Considering institutional infrastructure, we note the growing role of omic observation in active and increasingly interlinked marine networks, with examples such as EMBRC/ASSEMBLE, International Long Term Ecological Research Network, AtlantOS, National Association of Marine Labs, Smithsonian MarineGEO, and Partnership on Observation of the Global Oceans. We also note some key human elements essential to meeting the networks' goals, address how the community is evolving, and why performing seemingly simple tasks within a broadly distributed community presents significant challenges even among those who have agreed to use standards. From the perspectives above, we review lessons learned from use cases that leverage Genomic Observatories Network, such as the Autonomous Reef Monitoring Structures (ARMS), Ocean Sampling Day (OSD) and myOSD, which included experiences with citizen science. Looking forward, we survey 1) promising new technologies for in situ biological observation (e.g., cheap 3D printed omics samplers), 2) progress towards adoption of omics methods in marine policy and conservation programs, and 3) opportunities that a Genomic Observatory brings, alone or embedded in a network, to address novel scientific questions and support Essential Biodiversity Variables, Essential Ocean Variables, and indices such as the Ocean Health Index. Given the data intensive nature of omics investigation, we note emerging cyberinfrastructure solutions, such as the Genomic Observatories Metadatabase (GeOMe), an open-access repository for geographic and ecological metadata associated with biosamples, and predictive modeling efforts, such as those of the Island Digital Ecosystem Avatar (IDEA) Consortium. Finally, we explore the potential of Genomic Observatories as components of high-resolution calibration sites. Such observatories would provide super-contextualized "data trusts" for machine learning and artificial intelligence applications that draw on multi-omic observation.
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    Interoperability Across Ocean Research Infrastructures Through Use Of Ocean Best Practices (2019)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2019, San Francisco, California, USA, 2019-12-09-2019-12-13American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Description: Climate change and sustainable use of natural capital demand increased collaboration across the sciences. The first steps for effective collaboration often focus on improving interoperability between observation and analyses methodologies. This is traditionally done through a combination of standards and best practices. The ocean observation community and observing infrastructures - with regionally diverse members working in physics, chemistry, biology and engineering - is looking toward a dynamic consensus-building approach to match the rapid pace of technological evolution. This is an essential part of the long-term cooperation among ocean observing infrastructures. In the last 12 months, the ocean observing community has implemented an Ocean Best Practices System (OBPS). This System was recently adopted by the Intergovernmental Ocean Commission as an international project under GOOS and IODE. The System consists of a permanent OBPS repository hosted by IODE with state-of-the-art semantic discovery and metadata indexing for improved access to best practices and, eventually, to the data associated with them. There have been discussions to understand how to deal with differing best practices and standards on the same observation or analyses objective and other issues that arise from a comprehensive ocean best practices system. A recent survey, to be described, offers options on alternative approaches. Further, we have created a forum, in “Frontiers in Marine Science” for discussion of best practices and their applications. This presentation will cover options for evolving and sustaining ocean best practices across infrastructures. The recommendations build upon the community survey, the OGC experience, the outcomes of the OceanObs’19 conference as well as inputs from the Decade for Ocean Sciences community meetings. The extension of this work to other communities will also be examined.
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    Planet Microbe: An Ontology-Enriched Cyberinfrastructure System for FAIR Marine ‘Omics Data (2020)
    American Geophysical Union
    In:  EPIC3Ocean Sciences Meeting 2020, 2020-02-16-2020-02-21American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Repository Name: EPIC Alfred Wegener Institut
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    Managing the Evolution and Sustainability of Best Practices Across Ocean Science (2018)
    American Geophysical Union
    In:  EPIC32018 Ocean Sciences Meeting, Portland, Oregon, USA, 2018-02-11-2018-02-16American Geophysical Union
    Details
    Publication Date: 2020-02-12
    Description: Target audience: All ocean scientists who wish to share or discover best practice documents in their domain. Background: A working group convened under the AtlantOS project and including partners from ODIP, IODE, JCOMM, IEEE, and AWI is currently developing new technologies and approaches for handling best practices (BPs) across ocean science. The goal of the working group is to create a sustained repository for BPs, to ease their propagation and adoption. Goals: After briefly describing its work, the BP working group will engage town hall participants in a discussion on 1) how best to find and centrally archive BPs in participants' disciplines and 2) what capacities a central archive of BPs would need to help participants create, discover, share, and archive their BPs. The participant input gathered will be used to further the development of a multidisciplinary repository for BPs and better harmonise ocean observation.
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    Sedimentary perspectives of Pleistocene ocean circulation and climate change from the southernmost Chilean continental margin (2019)
    American Geophysical Union
    In:  EPIC3AGU Centennial Fall Meeting, San Francisco, CA, USA, 2019-12-09-2019-12-13American Geophysical Union
    Details
    Publication Date: 2020-05-14
    Description: IODP Exp. 383 recovered two Pleistocene sedimentary sequences from the upper continental slope along the southernmost Chilean margin that are well positioned to monitor changes in the Antarctic Circumpolar Current (ACC) upstream of the Drake Passage and the history of Patagonian glaciation. These sites are characterized by high sedimentation rates and a complex distribution of siliciclastic sediments with infrequent decimeter-scale beds of calcareous biogenic sediments. Unravelling ocean circulation and climate history from these sites requires a primary understanding of sedimentary provenance and transport mechanisms derived from a complete lithological characterization of the sequence. Here, we integrate downcore shipboard physical properties with sedimentological observations to fully characterize the sequences, evaluate potential for correlation and constrain regional depositional processes. Site U1542 (52°S; 1101 m water depth) consists of a 249 m spliced sedimentary sequence containing Middle Pleistocene to Holocene sediments. It mainly consists of clayey silt that is often interbedded with thin (~75 cm) beds of calcareous sand-bearing clayey to sandy silt with foraminifera and nannofossils or foraminifera-rich nannofossil ooze. Site U1544 (55°S; 2090 m water depth) consists of a 98 m sedimentary sequence obtained from a single hole. Sediments are also dominated by silty clay, but exhibit slightly thicker beds of calcareous ooze and a significantly higher proportion of cm- to dm-scale sand beds that are interpreted as turbidites. Based on the lithology of the recovered sediments and proximity to a glaciated continental margin, terrigenous sediment is likely delivered to these locations by a combination of ice rafting, glacial meltwater plumes, episodic downslope transport from the outer continental shelf and fine-grained sediments transported by the Cape Horn Current entering the Drake Passage as the northern branch of the ACC.
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    Antarctic Circumpolar Current Dynamics at the Pacific Entrance to the Drake Passage Over the Past 1.3 Million Years (2020)
    American Geophysical Union
    In:  EPIC3Paleoceanography and Paleoclimatology, American Geophysical Union, 35(7), pp. e2019PA003773, ISSN: 2572-4525
    Details
    Publication Date: 2021-02-01
    Description: The Antarctic Circumpolar Current (ACC) is the world's largest current system connecting all three major basins of the global ocean. Our knowledge of glacial‐interglacial changes in ACC dynamics in the southeast Pacific is not well constrained and presently only based on reconstructions covering the last glacial cycle. Here we use a combination of mean sortable silt grain size of the terrigenous sediment fraction (10–63 μm, "Sortable Silt") and X‐ray fluorescence scanner‐derived Zr/Rb ratios as flow strength proxies to examine ACC variations at the Pacific entrance to the Drake Passage (DP) in the vicinity of the Subantarctic Front. Our results indicate that at the DP entrance, ACC strength varied by ~6–16% on glacial‐interglacial time scales, yielding higher current speeds during interglacial times and reduced current speeds during glacials. We provide evidence that previous observations of a reduction in DP throughflow during the last glacial period are part of a consistent pattern extending for at least the last 1.3 Ma. The orbital‐scale cyclicity follows well‐known global climate changes from prevailing ca. 41‐kyr cycles in the early part of the record (1.3 Ma to 850 ka; marine isotope stage 21) across the mid‐Pleistocene transition into the middle and late Pleistocene 100‐kyr world. A comparison to a bottom water flow record from the deep western boundary current off New Zealand (Ocean Drilling Program Site 1123) reveals anti‐phased changes between the two sites. The enhanced supply of deep water along the DP and into the Atlantic Ocean during interglacials corresponds to a weakened flow of the SW Pacific deep western boundary current.
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    Scenario analysis can guide aquaculture planning to meet sustainable future production goals (2021)
    Oxford University Press
    In:  EPIC3ICES Journal of Marine Science, Oxford University Press, pp. 1-11, ISSN: 1054-3139
    Details
    Publication Date: 2021-07-23
    Description: Marine aquaculture holds great promise for meeting increasing demand for healthy protein that is sustainably produced, but reaching necessary production levels will be challenging. The ecosystem approach to aquaculture is a framework for sustainable aquaculture development that prioritizes multiple-stakeholder participation and spatial planning. These types of approaches have been increasingly used to help guide sustainable, persistent, and equitable aquaculture planning, but most countries have difficulties in setting or meeting longer-term development goals. Scenario analysis (SA) for future planning uses similar approaches and can complement holistic methods, such as the ecosystem approach to aquaculture framework, by providing a temporal analogue to the spatially robust design. Here we define the SA approach to planning in aquaculture, outline how SA can benefit aquaculture planning, and review how this tool is already being used. We track the use of planning tools in the 20 International Council for the Exploration of the Sea member nations, with particular attention given to Norway’s development goals to 2050. We conclude that employing a combination of an ecosystem framework with scenario analyses may help identify the scale of development aquaculture goals over time, aid in evaluating the feasibility of the desired outcomes, and highlight potential social-ecological conflicts and trade-offs that may otherwise be overlooked.
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    Near-shore submarine permafrost of the central Laptev Sea, East Siberia (2015)
    American Geophysical Union
    In:  EPIC3American Geophysical Union, Fall Meeting 2015, San Francisco, 2015San Francisco, American Geophysical Union
    Details
    Publication Date: 2016-10-26
    Description: Coastal erosion and relative sea-level rise inundate terrestrial permafrost with seawater and create submarine permafrost. Once flooded, permafrost begins to warm under marine conditions, which can destabilize the sea floor. The timing of inundation can be inferred from the rate of coastline retreat and the distance from the shoreline. Coastline retreat rates are inversely related to the inclination of the upper surface of submarine ice-bonded permafrost. Submarine permafrost thaw is considered to be a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the East Siberian shelf. A 52 m long core drilled from the sea ice in Buor Khaya Bay, central Laptev Sea revealed unfrozen sediment overlying ice-bonded permafrost. Dissolved methane and sulfate concentrations are inversely related along the core with higher methane and lower sulfate contents in the ice-bonded submarine permafrost relative to the overlying unfrozen sediment. The observed profiles of sediment pore water sulfate concentrations, as well as methane concentrations and methane stable carbon isotope ratios, indicate that methane from ice-bonded permafrost is oxidized at or immediately following thaw. Anaerobic oxidation of methane in the unfrozen sediment column between ice-bonded permafrost and the seabed makes it unlikely that methane from thawing submarine permafrost could reach the seabed.
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    Unprecedented permafrost thaw dynamics on a decadal time scale: Batagay mega thaw slump development, Yana Uplands, Yakutia, Russia (2016)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, San Francisco, USA, 2016-12-12-2016-12-16San Francisco, American Geophysical Union
    Details
    Publication Date: 2016-12-23
    Description: Ice-rich permafrost that formed in glacial periods of the Quaternary is highly vulnerable to thaw under ongoing climate warming and anthropogenic disturbance. The mega thaw slump near the village of Batagay (Yakutia, Russia) is an outstanding example of permafrost degradation and demonstrates that thermo-erosion processes may occur in unexpected locations, develop very rapidly in particular after disturbances, and leave behind deep rutted badlands. Retrogressive thaw slumps are particularly frequent along riverbanks and coastlines of regions where buried glacier ice or ice-rich glacial till have been mapped. In East Siberia, syngenetic Late Pleistocene Ice Complex (Yedoma) permafrost deposits accumulate volumetric ground ice contents of up to 80-90% % and extend tens of meters below the ground surface. Beyond the Yedoma main distributional range in the coastal lowlands of the Laptev and East Siberian seas, these deposits are also found on slopes of the Verkhoyan Mountain Range and in valleys of surrounding foothills, providing favorable preconditions for rapid thaw development. The Batagay mega slump exposes a profile of 30m thick Yedoma deposits underlain by ice saturated alluvial sand of around 60 m thickness and another very ice-rich layer at the base. We present data from a multi-sensor remote sensing time series investigation of the mega slump in order to assess the planimetric and volumetric dimensions and its decadal and interannual expansion rates. For ortho-rectification purposes and for volumetric analyses, we photogrammetrically derived highly detailed digital elevation models. The height difference between the headwall and the slump outflow is 145 m along a distance of 2300 m, while the maximum slump width is 840 m. Our analysis does not show any signs of stabilization after several decades (since 1980s) of slump growth, with the headwall retreating with observed rates of generally 〉10 m and more recently up to 30m per year. Reconstruction of a paleo-surface revealed that the slump has carved into the rolling topography to a depth of up to 73 m. The current size of the slump is 〉69 ha, while it had thawed 〉25 × 106 m³ of ice-rich permafrost through 2016. The majority of sediment released from the slump episodically dams up the Batagay River, forming a large temporary lake which then empties catastrophically.
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    Scientists spend Arctic winter adrift on sea ice (2016)
    American Geophysical Union
    In:  EPIC3EOS, American Geophysical Union
    Details
    Publication Date: 2017-01-19
    Repository Name: EPIC Alfred Wegener Institut
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    The Mozambique Ridge: a document of massive multi-stage magmatism (2017)
    Oxford University Press
    In:  EPIC3Geophysical Journal International, Oxford University Press, 208(1), pp. 449-467, ISSN: 1365-246X
    Details
    Publication Date: 2016-12-03
    Description: The Mozambique Ridge, a prominent basement high in the southwestern Indian Ocean, consists of four major geomorphological segments associated with numerous phases of volcanic activity in the Lower Cretaceous. The nature and origin of the Mozambique Ridge have been intensely debated with one hypothesis suggesting a Large Igneous Province origin. High-resolution seismic reflection data reveal a large number of extrusion centres with a random distribution throughout the southern Mozambique Ridge and the nearby Transkei Rise. Intra-basement reflections emerge from the extrusion centres and are interpreted to represent massive lava flow sequences. Such lava flow sequences are characteristic of eruptions leading to the formation of continental and oceanic flood basalt provinces, hence supporting a Large Igneous Province origin of the Mozambique Ridge. We observe evidence for widespread post-sedimentary magmatic activity that we correlate with a southward propagation of the East African Rift System. Based on our volumetric analysis of the southern Mozambique Ridge we infer a rapid sequential emplacement between ~131 Ma and ~125 Ma, which is similar to the short formation periods of other Large Igneous Provinces like the Agulhas Plateau.
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    Submarine Landslides along the Siberian part of Lomonosov Ridge: Triggering Mechanisms, Timing and Significance (2015)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting, 2015-12-14-2015-12-18American Geophysical Union
    Details
    Publication Date: 2016-10-30
    Repository Name: EPIC Alfred Wegener Institut
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    Ocean acidification alleviates low-temperature effects on growth and photosynthesis of the red alga Neosiphonia harveyi (Rhodophyta) (2013)
    Oxford University Press
    In:  EPIC3Journal of Experimental Botany, Oxford University Press, ISSN: 0022-0957
    Details
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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    Combining terrestrial, air-, and space-borne remote sensing for permafrost thaw subsidence change detection in Arctic Alaska (2017)
    American Geophysical Union
    In:  EPIC3AGU Fall Meeting 2017, Ernest N. Morial Convention Center, New Orleans, Louisiana, USA, 2017-12-11-2017-12-15New Orleans, Louisiana, USA, American Geophysical Union
    Details
    Publication Date: 2018-04-06
    Description: The unique feature of permafrost in the Arctic is the presence of a large amount of ice below the earth surface. Thermal degradation and subsequent permafrost destabilization causes thaw subsidence and thermokarst development. Because these processes are difficult to detect due to the lack of timely and accurate elevation datasets they have received not much attention, despite their potentially global significance through the permafrost carbon feedback. Thanks to remote sensing pioneering works in Alaska and Siberia, widespread thaw subsidence has been documented and is increasingly perceived as a potentially widespread permafrost landscape response to contemporary climate change. Clearly, however, detailed local inventories are required to calibrate regional long and short-term assessments for measuring surface deformation due to permafrost thaw. The objective of our study is to analyze time series of repeat terrestrial, air-, and space borne laser scanning (rLiDAR) for quantification of land surface lowering due to permafrost thaw, which is poorly resolved in terms of recent landscape development in the Arctic. Our work aims at finding commonalities and differences of change or no change on ground-ice-rich primary surfaces that are preserved as uplands, which cover 15 to 20% of the Teshekpuk Lake Special Area on the Arctic Coastal Plain of northern Alaska. Our approach focuses on quantifying modern thaw subsidence and thermokarst rates with high spatial resolution data over several decades as well as high temporal resolution data of inter-annual intervals. Multi-annual measurements of rLiDAR over Arctic Alaska have been made by aircraft in 2016 and in 2015+2017 through on-site surveys during field expeditions. These in situ data serve as a basis for large scale surface change assessments using time series of photogrammetrically derived elevation data from very high resolution historical aerial photographs and modern satellite imagery. The synergistic data fusion approach enhances permafrost degradation monitoring and better resolves surface deformation associated with thaw subsidence. The novel datasets also provide insights into previously unrecognized patterns of rapid permafrost thaw and related interconnections.
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    The first known virus isolates from Antarctic sea ice have complex infection patterns (2018)
    Oxford University Press
    In:  EPIC3FEMS Microbiology Ecology, Oxford University Press, 94(4), pp. 1-15, ISSN: 1574-6941
    Details
    Publication Date: 2018-11-09
    Repository Name: EPIC Alfred Wegener Institut
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    Contribution of Convection-Induced Heat Flux to Winter Ice Decay in the Western Nansen Basin (2018)
    American Geophysical Union
    In:  EPIC3Journal of Geophysical Research: Oceans, American Geophysical Union, ISSN: 2169-9275
    Details
    Publication Date: 2018-09-20
    Description: Gradually decaying Arctic sea ice changes the boundary conditions at the surface, separating ocean and atmosphere. In recent years, substantial reductions in sea ice during winter have been observed in the Atlantic sector of the Arctic Ocean, which forms the gateway for warm water inflow from the midlatitudes. In this study, we used routine output from the Mercator Ocean global operational system (MOGOS) to assess the efficiency of winter thermohaline convection transporting heat from deep layers to the ocean surface along the Atlantic origin water (AW) pathway, between Svalbard and Franz Joseph Land in the Nansen Basin. Positive temperature extremes in the AW layer in midwinter promote favorable prerequisite conditions for deep‐reaching thermohaline convection, with explicit signs captured by the MOGOS. Balance equations with several assumptions for the compact region around the position (81.30°N, 31°E) of the long‐term (2004–2010) mooring demonstrated that winter heat loss at the ocean surface is mainly compensated by convective heat flux from the AW layer. Heat and salt fluxes, associated with horizontal advection, are compatible with convective fluxes, while contribution of ice formation/melt is substantially smaller. Conclusion about the dominant role of vertical convection in shaping thermohaline structure and reducing sea ice in winter is supported by correlation analysis of the MOGOS output and mooring‐based measurements. Unfavorable background conditions (thick and consolidated sea ice in combination with specific directions of ice drift) may significantly alter convection development, as demonstrated for two sequential years with substantially different external forcing.
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    Microearthquake activity, lithospheric structure, and deformation modes at an amagmatic ultraslow spreading Southwest Indian Ridge segment (2016)
    American Geophysical Union
    In:  EPIC3Geochemistry, Geophysics, Geosystems, American Geophysical Union, 17(7), pp. 2905-2921
    Details
    Publication Date: 2016-09-11
    Description: While nascent oceanic lithosphere at slow to fast spreading mid-ocean ridges (MOR) is relatively well studied, much less is known about the lithospheric structure and properties at ultraslow MORs. Here we present microearthquake data from a 1 year ocean bottom seismometer deployment at the amagmatic, oblique supersegment of the ultraslow spreading Southwest Indian Ridge. A refraction seismic experiment was performed to constrain upper lithosphere P-velocities and results were used to construct a 1D velocity model for earthquake location. Earthquake foci were located individually and subsequently relocated relative to each other to sharpen the image of seismically active structures. Frequent earthquake activity extends to 31 km beneath the seafloor, indicating an exceptionally thick brittle lithosphere and an undulating brittle-ductile transition that implies significant variations in the along-axis thermal structure of the lithosphere. We observe a strong relation between petrology, microseismicity distribution, and topography along the ridge axis: Peridotite-dominated areas associate with deepest hypocenters, vast volumes of lithosphere that deforms aseismically as a consequence of alteration, and the deepest axial rift valley. Areas of basalt exposure correspond to shallower hypocenters, shallower and more rugged axial seafloor. Focal mechanisms deviate from pure extension and are spatially variable. Earthquakes form an undulating band of background seismicity and do not delineate discrete detachment faults as common on slow spreading ridges. Instead, the seismicity band sharply terminates to the south, immediately beneath the rift boundary. Considering the deep alteration, large steep boundary faults might be present but are entirely aseismic.
    Repository Name: EPIC Alfred Wegener Institut
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  • 92
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    Taxonomy of planktonic microbial eukaryotes (2017)
    Oxford University Press
    In:  EPIC3Marine Plankton, Marine Plankton, Oxford University Press, 704 p., ISBN: 9780199233267
    Details
    Publication Date: 2017-05-11
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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    Sampling, preservation, and counting of samples i) Phytoplankton (2017)
    Oxford University Press
    In:  EPIC3Marine Plankton, Marine Plankton, Oxford University Press, 704 p., ISBN: 9780199233267
    Details
    Publication Date: 2017-04-28
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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    Diatoms (2017)
    Oxford University Press
    In:  EPIC3Marine Plankton, Marine Plankton, Oxford University Press, 704 p., ISBN: 9780199233267
    Details
    Publication Date: 2017-05-11
    Repository Name: EPIC Alfred Wegener Institut
    Type: Inbook , peerRev
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  • 95
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    High resolution velocity structure beneath Mount Vesuvius from seismic array data (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: A high resolution P-wave image of Mt. Vesuvius edifice has been derived from simultaneous inversion of travel times and hypocentral parameters of local earthquakes, land based shots and small aperture array data. The results give detailsdownto300 – 500m.Therelocatedlocalseismicity appears to extend down to 5 km below the central crater, distributed in a major cluster, centered at 3 km below the central crater and in a minor group, with diffuse hypocenters inside the volcanic edifice. The two clusters are separated by an anomalously high Vp region at around 1 km depth. A zone with high Vp/Vs in the upper layers is interpreted as produced by the presence of intense fluid circulation. The highest energy quakes (up to M = 3.6) are located in the deeper cluster, in a high P-wave velocity zone. Our results favor an interpretation in terms of absence of shallow magma reservoirs.
    Description: Published
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Velocity Tomography ; Mt. Vesuvius ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Topography of the Calabria subduction zone (southern Italy): Clues for the origin of Mt. Etna (2011)
    American Geophysical Union
    Details
    Publication Date: 2012-02-03
    Description: Calabria represents an ideal site to analyze the topography of a subduction zone as it is located on top of a narrow active Wadati-Benioff zone and shows evidence of rapid uplift. We analyzed a pattern of surface deformation using elevation data with different filters and showed the existence of a long wavelength (〉100 km) relatively positive topographic signal at the slab edges. The elevation of MIS 5.5 stage marine terraces supports this pattern, although the record is incomplete and partly masked by the variable denudation rate. We performed structural analyses along the major active or recently reactivated normal faults showing that the extensional direction varies along the Calabrian Arc and laterally switches from arc-normal, within the active portion of the slab, to arc-oblique or even arc-parallel, along the northern and southern slab edges. This surface deformation pattern was compared with a recent high resolution P wave tomographic model showing that the high seismic velocity anomaly is continuous only within the active Wadati-Benioff zone, whereas the northern and southwestern sides are marked by low velocity anomalies, suggesting that large-scale topographic bulges, volcanism, and uplift could have been produced by mantle upwelling. We present numerical simulations to visualize the three-dimensional mantle circulation around a narrow retreating slab, ideally similar to the one presently subducting beneath Calabria. We emphasize that mantle upwelling and surface deformation are expected at the edges of the slab, where return flows may eventually drive decompression melting and the Mount Etna volcanism.
    Description: Published
    Description: TC1003
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: topography ; Calabrian Arc ; subduction ; tomography ; mantle flow ; uplift ; retreat ; anisotropy ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    The 16 November 2006 flank collapse of the south-east crater at Mount Etna, Italy: Study of the deposit and hazard assessment (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: On 16 November 2006 a flank collapse affected the unstable eastern slope of the South-East Crater (SEC) of Mount Etna. The collapse occurred during one of the paroxysmal events with sustained strombolian activity that characterized the August–December 2006 eruption and was triggered by erosion of loose, hydrothermally altered material of the steep south-east sector of SEC from the outpour of lava. The collapse produced a debris avalanche that involved both lithic and juvenile material and resulted in a deposit emplaced on the eastern flank of the volcano up to 1.2 km away from the source. The total volume of the deposit was estimated to be in the order of 330,000–413,000 m3. The reconstruction of the collapse event was simulated using TITAN2D software designed to model granular avalanches and landslides. This approach can be used to estimate areas that may be affected by similar collapse events in the future. The area affected by the 16 November 2006 lateral collapse of SEC was a small portion of the Mount Etna summit area, but the fact that no one was killed or injured should be considered fortuitous. The summit and adjacent areas of the volcano, in fact, are usually visited by many tourists who are not prepared to face this type of danger. The 16 November 2006 collapse points to the need to be prepared for similar events through scientific investigation (analysis of flank instability, numerical simulation of flows) and development of specific civil protection plans.
    Description: Published
    Description: B02204
    Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani
    Description: JCR Journal
    Description: reserved
    Keywords: Mount Etna ; flank instability ; volcaniclastic deposit ; granular flows ; numerical simulation ; volcanic hazard ; 04. Solid Earth::04.08. Volcanology::04.08.08. Volcanic risk
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Seismic and landslide source of the 1908 Straits of Messina tsunami (Sicily, Italy) (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: One hundred years ago (December 1908) a devastating tsunami associated with an earthquake struck the Straits of Messina area, causing many casualties. On the basis of seismic data and observed runups and arrival times, we suggest that the tsunami was likely generated by coseismic seafloor displacement coupled with a small submarine landslide triggered by the earthquake. Backwards ray-tracing using a depth-dependent velocity field, submarine slope analysis and inferences form the main drainage network allowed us to identify possible locations for the source of the submarine landslide. We then performed direct simulations of tsunamis generated by the earthquake and landslides and identified the tsunami source (earthquake plus landslide) that best fits observational data in a small volume submarine landslide (1–5 km3) located offshore Nizza, Sicily.
    Description: Published
    Description: L16304
    Description: 3.7. Dinamica del clima e dell'oceano
    Description: 4.2. TTC - Modelli per la stima della pericolosità sismica a scala nazionale
    Description: 4.6. Oceanografia operativa per la valutazione dei rischi in aree marine
    Description: JCR Journal
    Description: reserved
    Keywords: earthquake ; landslide ; tsunami ; 03. Hydrosphere::03.01. General::03.01.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 05. General::05.01. Computational geophysics::05.01.03. Inverse methods
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Kinematics and Source Zone Properties of the 2004 Sumatra-Andaman Earthquake and Tsunami: Nonlinear Joint Inversion of Tide-Gage, Satellite Altimetry and GPS data (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: We (re)analyzed the source of the 26 December 2004 Sumatra-Andaman earthquake and tsunami through a nonlinear joint inversion of an in-homogeneous dataset made up of tide-gages, satellite altimetry, and far-field GPS recordings. The purpose is two-fold: (1) the retrieval of the main kinematics rupture parameters (slip, rake, rupture velocity); (2) the inference of the rigidity of the source zone. We independently estimate the slip from tsunami data and the seismic moment from geodetic data, so to derive the rigidity. Our results confirm that the source of the 2004 Sumatra-Andaman earthquake has a complex geometry, constituted by three main slip patches, with slip peaking at ~30 meters in the Southern part of the source. The rake direction rotates counter-clockwise at North, according to the direction of convergence along the trench. The rupture velocity is higher in the deeper than in the shallower part of the source, consistently with the expected increase of rigidity with depth. It is also lower in the Northern part, consistently with known variations of the incoming plate properties and shear velocity. Our model features a rigidity (20-30 GPa), that is lower than PREM average for the seismogenic volume [Dziewonski and Anderson, 1981]. The source rigidity is one of the factors controlling the tsunamigenesis: for a given seismic moment, the lower the rigidity, the higher the induced seafloor displacement. The general consistence between our source model and previous studies supports the effectiveness of our approach to the joint inversion of geodetic and tsunami data for the rigidity estimation.
    Description: In press
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: Source process ; Sumatra ; Tsunami ; joint inversion ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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    Laboratory measurements of the frictional properties of the Zuccale 3 low-angle normal fault, Elba Island, Italy (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: Using a case study from the island of Elba, Italy, we seek to test the hypothesis that 7 the presence of minerals with low frictional strengths can explain prolonged slip on 8 low-angle normal faults. The central core of the Zuccale low-angle normal fault 9 contains a distinctive fault rock zonation that developed during progressive exhumation. 10 Most fault rock components preserve microstructural evidence for having accommodated 11 deformation entirely, or partly, by frictional mechanisms. One millimeter thick sample 12 powders of all the major fault rock components were deformed in a triaxial deformation 13 apparatus under water-saturated conditions, at room temperature, and at constant effective 14 normal stresses of 25, 50, and 75 MPa. Pore fluid pressure was maintained at 50 MPa 15 throughout. Overall, the coefficient of friction (m) of the fault rocks varies between 16 0.25 and 0.8, emphasizing the marked strength heterogeneity that may exist within 17 natural fault zones. Also, m is strongly dependent on fault rock mineralogy and is 18 〈0.45 for fault rocks containing talc, chlorite, and kaolinite and 〉0.6 for fault rocks 19 dominated by quartz, dolomite, calcite, and amphibole. Localization of frictional slip 20 within talc-rich portions of the fault core can potentially explain movements along the 21 Zuccale fault over a wide range of depths within the upper crust, although the 22 mechanical importance of the talc-bearing fault rocks likely decreased following their 23 dismemberment into a series of poorly connected fault rock lenses. Additionally, slip 24 within clay-bearing fault gouges with m between 0.4 and 0.5 may have facilitated 25 movements in the uppermost (〈2 km) crust. For several other fault rock components, 26 m varies between 0.5 and 0.8, and mineralogical weakening alone is insufficient to 27 account for low-angle slip. In the latter fault rock components, other weakening 28 mechanisms such as the development of high fluid pressures, or dissolution-precipitation 29 creep, may have been particularly important in reducing fault strength.
    Description: In press
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: Friction ; Low-Angle Normal Faults ; Experiments ; Weakening ; 04. Solid Earth::04.04. Geology::04.04.06. Rheology, friction, and structure of fault zones
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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