ALBERT

Description: To identify greater detail in the seismicity pattern preceding the 24 August 2016 Mw6.0 earthquake in Central Italy, we apply waveform matching using 1,028 events as templates. In the 8 months before the mainshock, we find ~2,000 additional earthquakes mostly located along a subhorizontal shear zone (SZ) bounding at depth the extensional fault system. Asynchrony is observed in the occurrence of events nucleating along the SZ compared to the ones on fault portions embedded in the shallower upper crust, with the former anticipating the latter. Within the SZ, we also observe along-strike seismic migration episodes with earthquakes pointing toward the Mw6.0 mainshock nucleation zone. These episodes are followed by an apparent quiescence within the main fault area. We suggest that the variations in the seismic activity along the SZ represent the brittle signature of the tectonic loading process enabling portions of the overlaying normal faults to become unlocked.

Description: Published

Description: 12170–12180

Description: 6T. Variazioni delle caratteristiche crostali e precursori

Description: JCR Journal

Description: Earthquake interaction and stress change on nearby faults by afterslip, static and dynamic triggering play an important role in the activation of major events. We apply a matched filter technique to augment the detected events in the time window between the two main shocks of 20 (Mw 6.1) and 29 (Mw 6.0) May 2012, during the Emilia seismic sequence (Italy). From 1,727 well-located templates, we increase the number of detections to 7,616 lowering the completeness magnitude of approximately 0.6 degrees. This greater detail allows evidencing migrations of seismic events from the nucleation point of the first shock to the second. The seismicity pattern suggests a transient aseismic slip acting immediately after the shallow first event, weakening and loading the volume around the deep nucleation point of the 29 May 2012 Mw6.0 earthquake. Repeating earthquakes are also found between the two main-shocks. The released cumulative slip, estimated from the earliest repeating earthquake amounts to approximately 27 cm at a depth of about 7 km within the first 5 hours after the 20 May Mw6.1. Migrations and repeaters could represent the fingerprint of an early afterslip triggered by the first mainshock.

Description: Published

Description: 625-635

Description: 2T. Deformazione crostale attiva

Description: JCR Journal

Description: There was a typographical error in [1, eq. (18)]. Instead of (Formula Presented). The equation describes the second-order statistics of the interferometric phases. Its significance lies in the fact that from it, one can derive the statistical properties of a wide range of quantities estimated from an interferometric stack, including the closure phases that we addressed in the paper. The other equations, numerical results, and the conclusions remain unaffected, because the error was of a purely typographical nature.

Description: Coastal erosion and flooding transform terrestrial landscapes into marine environments. In the Arctic, these processes inundate terrestrial permafrost with seawater and create submarine permafrost. Permafrost begins to warm under marine conditions, which can destabilize the sea floor and may release greenhouse gases. We report on the transition of terrestrial to submarine permafrost at a site where the timing of inundation can be inferred from the rate of coastline retreat. On Muostakh Island in the central Laptev Sea, East Siberia, changes in annual coastline position have been measured for decades and vary highly spatially. We hypothesize that these rates are inversely related to the inclination of the upper surface of submarine ice-bonded permafrost (IBP) based on the consequent duration of inundation with increasing distance from the shoreline. We compared rapidly eroding and stable coastal sections of Muostakh Island and find permafrost-table inclinations, determined using direct current resistivity, of 1 and 5 %, respectively. Determinations of submarine IBP depth from a drilling transect in the early 1980s were compared to resistivity profiles from 2011. Based on borehole observations, the thickness of unfrozen sediment overlying the IBP increased from 0 to 14m below sea level with increasing distance from the shoreline. The geoelectrical profiles showed thickening of the unfrozen sediment overlying ice-bonded permafrost over the 28 years since drilling took place. We use geoelectrical estimates of IBP depth to estimate permafrost degradation rates since inundation. Degradation rates decreased from over 0.4ma-1 following inundation to around 0.1ma-1 at the latest after 60 to 110 years and remained constant at this level as the duration of inundation increased to 250 years. We suggest that long-term rates are lower than these values, as the depth to the IBP increases and thermal and porewater solute concentration gradients over depth decrease. For the study region, recent increases in coastal erosion rate and changes in benthic temperature and salinity regimes are expected to affect the depth to submarine permafrost, leading to coastal regions with shallower IBP.

Description: Transient simulations are widely used in studying the past climate as they provide better comparison with any exisiting proxy data. However, multi-millennial transient simulations using coupled climate models are usually computationally very expensive. As a result several acceleration techniques are implemented when using numerical simulations to recreate past climate. In this study, we compare the results from transient simulations of the present and the last interglacial with and without acceleration of the orbital forcing, using the comprehensive coupled climate model CCSM3 (Community Climate System Model 3). Our study shows that in low-latitude regions, the simulation of long-term variations in interglacial surface climate is not significantly affected by the use of the acceleration technique (with an acceleration factor of 10) and hence, large-scale model-data comparison of surface variables is not hampered. However, in high-latitude regions where the surface climate has a direct connection to the deep ocean, e.g. in the Southern Ocean or the Nordic Seas, acceleration-induced biases in sea-surface temperature evolution may occur with potential influence on the dynamics of the overlying atmosphere. The data provided here are from both accelerated and non-accelerated runs as decadal mean values.

Description: Abrupt millennial-scale climate change events of the last deglaciation (i.e. Heinrich Stadial 1 and the Younger Dryas) were accompanied by marked increases in atmospheric CO2 (CO2atm) and decreases in its stable carbon isotopic ratios (d13C), i.e. d13CO2atm, presumably due to outgassing from the ocean. However, information on the preceding Heinrich Stadials during the last glacial period is scarce. Here we present d13C records from two species of planktonic foraminifera from the western South Atlantic that reveal major decreases (up to 1 per mil) during Heinrich Stadials 3 and 2. These d13C decreases are most likely related to millennialscale periods of weakening of the Atlantic meridional overturning circulation and the consequent increase (decrease) in CO2atm (d13CO2atm). We hypothesise two mechanisms that could account for the decreases observed in our records, namely strengthening of Southern Ocean deep-water ventilation and weakening of the biological pump. Additionally, we suggest that air?sea gas exchange could have contributed to the observed d13C decreases. Together with other lines of evidence, our data are consistent with the hypothesis that the CO2 added to the atmosphere during abrupt millennial-scale climate change events of the last glacial period also originated in the ocean and reached the atmosphere by outgassing. The temporal evolution of d13C during Heinrich Stadials 3 and 2 in our records is characterized by two relative minima separated by a relative maximum. This ?w structure? is also found in North Atlantic and South American records, further suggesting that such a structure is a pervasive feature of Heinrich Stadial 2 and, possibly, also Heinrich Stadial 3.

Description: To address growing concern over the effects of fisheries non-target catch on elasmobranchs worldwide, the accurate reporting of elasmobranch catch is essential. This requires data on a combination of measures, including reported landings, retained and discarded non-target catch, and post-discard survival. Identification of the factors influencing discard vs. retention is needed to improve catch estimates and to determine wasteful fishing practices. To do this we compared retention rates of elasmobranch non-target catch in a broad subset of fisheries throughout the world by taxon, fishing country, and gear. A regression tree and random forest analysis indicated that taxon was the most important determinant of retention in this dataset, but all three factors together explained 59% of the variance. Estimates of total elasmobranch removals were calculated by dividing the FAO global elasmobranch landings by average retention rates and suggest that total elasmobranch removals may exceed FAO reported landings by as much as 400%. This analysis is the first effort to directly characterize global drivers of discards for elasmobranch non-target catch. Our results highlight the importance of accurate quantification of retention and discard rates to improve assessments of the potential impacts of fisheries on these species.