ALBERT

Description: This article has been accepted for publication in Geophysical Journal International ©:The Author(s) 2020. 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. All rights reserved.

Description: In volcanoes, topography, shallow heterogeneity and even shallow morphology can substan- tially modify seismic coda signals. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independently from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. Here, we apply the Multiple Lapse Time Window Analysis (MLTWA) to measure the relative importance of scattering attenuation vs absorption at Mount St Helens volcano before its 2004 erup- tion. The results show the characteristic dominance of scattering attenuation in volcanoes at lower frequencies (3–6 Hz), while absorption is the primary attenuation mechanism at 12 and 18 Hz. Scattering attenuation is similar but seismic absorption is one order of magnitude lower than at open-conduit volcanoes, like Etna and Kilauea, a typical behaviour of a (rela- tively) cool magmatic plumbing system. Still, the seismic albedo (measuring the ratio between seismic energy emitted and received from the area) is anomalously high (0.95) at 3 Hz. A radiative-transfer forward model of far- and near-field envelopes confirms this is due to strong near-receiver scattering enhancing anomalous phases in the intermediate and late coda across the 1980 debris avalanche and central crater. Only above this frequency and in the far-field diffusion onsets at late lapse times. The scattering and absorption parameters derived from MLTWA are used as inputs to construct 2-D frequency-dependent bulk sensitivity kernels for the S-wave coda in the multiple-scattering (using the Energy Transport Equations—ETE) and diffusive (AD, independent of MLTWA results) regimes. At 12 Hz, high coda-attenuation anomalies characterize the eastern side of the volcano using both kernels, in spatial correla- tion with low-velocity anomalies from literature. At 3 Hz, the anomalous albedo, the forward modelling, and the results of the tomographic imaging confirm that shallow heterogeneity beneath the extended 1980 debris-avalanche and crater enhance anomalous intermediate and late coda phases, mapping shallow geological contrasts. We remark the effect this may have on coda-dependent source inversion and tomography, currently used across the world to image and monitor volcanoes. At Mount St Helens, higher frequencies and deep borehole data are necessary to reconstruct deep volcanic structures with coda waves.

Description: Scottish Alliance for Geosciences Environment and Society and the Kleinman Grant for Volcano Research

Description: Published

Description: 169-188

Description: 1T. Struttura della Terra

Description: 2V. Struttura e sistema di alimentazione dei vulcani

Description: 3IT. Calcolo scientifico

Description: JCR Journal

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: Mud volcanoes are geological systems often characterized by elevated fluid pressures at depth deviating from hydrostatic conditions. This near-critical state makes mud volcanoes particularly sensitive to external forcing induced by natural or man-made perturbations. We used the Nirano mud volcanic field as a natural laboratory to test pre- and post-seismic effects generated by distant earthquakes.We first characterized the subsurface structure of the Nirano mud volcanic field with a geoelectrical study. Next, we deployed a broad-band seismic station in the area to understand the typical seismic signal generated by the mud volcano. Seismic records show a background noise below 2 s, sometimes interrupted by pulses of drumbeatlike high-frequency signals lasting from several minutes to hours. To date this is the first observation of drumbeat signal observed in mud volcanoes. In 2013 June we recorded a M4.7 earthquake, that occurred approximately 60 km far from our seismic station. According to empirical estimations the Nirano mud volcanic field should not have been affected by the M4.7 earthquake. Yet, before the seismic event we recorded an increasing amplitude of the signal in the 10–20 Hz frequency band. The signal emerged approximately two hours before the earthquake and lasted for about three hours. Our statistical analysis suggests the presence of a possible precursory signal about 10 min before the earthquake.

Description: Published

Description: 907–917

Description: 7A. Geofisica per il monitoraggio ambientale

Description: JCR Journal

Description: Author Posting. © The Authors, 2018. This article is posted here by permission of The Royal Astronomical Society for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 215 (2018): 713–735, doi:10.1093/gji/ggy313.

Description: Gas flux in volcanic conduits is often associated with long-period oscillations known as seismic tremor (Lesage et al.; Nadeau et al.). In this study, we revisit and extend the ‘magma wagging’and ‘whirling’models for seismic tremor, in order to explore the effects of gas flux on the motion of a magma column surrounded by a permeable vesicular annulus (Jellinek & Bercovici; Bercovici et al.; Liao et al.). We find that gas flux flowing through the annulus leads to a Bernoulli effect, which causes waves on the magma column to become unstable and grow. Specifically, the Bernoulli effects are associated with torques and forces acting on the magma column, increasing its angular momentum and energy. As the displacement of the magma column becomes large due to the Bernoulli effect, frictional drag on the conduit wall decelerates the motions of the column, restoring them to small amplitude. Together, the Bernoulli effect and the damping effect contribute to a self-sustained wagging-and-whirling mechanism that help explain the longevity of long-period seismic tremor.

Description: This work was supported by National Science Foundation grants EAR-1344538 and EAR-1645057

Description: We present the first application of a time reverse location method in a volcanic setting, for a family of long-period (LP) events recorded on Mt Etna. Results are compared with locations determined using a full moment tensor grid search inversion and cross-correlation method. From 2008 June 18 to July 3, 50 broad-band seismic stations were deployed on Mt Etna, Italy, in close proximity to the summit. Two families of LP events were detected with dominant spectral peaks around 0.9 Hz. The large number of stations close to the summit allowed us to locate all events in both families using a time reversal location method. The method involves taking the seismic signal, reversing it in time, and using it as a seismic source in a numerical seismic wave simulator where the reversed signals propagate through the numerical model, interfere constructively and destructively, and focus on the original source location. The source location is the computational cell with the largest displacement magnitude at the time of maximum energy current density inside the grid. Before we located the two LP families we first applied the method to two synthetic data sets and found a good fit between the time reverse location and true synthetic location for a known velocity model. The time reverse location results of the two families show a shallow seismic region close to the summit in agreement with the locations using a moment tensor full waveform inversion method and a cross-correlation location method.

Description: Published

Description: 452-462

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: We present the first application of a time reverse location method in a volcanic setting, for a family of long-period (LP) events recorded on Mt Etna. Results are compared with locations determined using a full moment tensor grid search inversion and cross-correlation method. From 2008 June 18 to July 3, 50 broad-band seismic stations were deployed on Mt Etna, Italy, in close proximity to the summit. Two families of LP events were detected with dominant spectral peaks around 0.9 Hz. The large number of stations close to the summit allowed us to locate all events in both families using a time reversal location method. The method involves taking the seismic signal, reversing it in time, and using it as a seismic source in a numerical seismic wave simulator where the reversed signals propagate through the numerical model, interfere constructively and destructively, and focus on the original source location. The source location is the computational cell with the largest displacement magnitude at the time of maximum energy current density inside the grid. Before we located the two LP families we first applied the method to two synthetic data sets and found a good fit between the time reverse location and true synthetic location for a known velocity model. The time reverse location results of the two families show a shallow seismic region close to the summit in agreement with the locations using a moment tensor full waveform inversion method and a cross-correlation location method.

Description: In press

Description: (11)

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: Stress can undergo rapid temporal changes in volcanic environments, and this is particularly true during eruptions. We use two independent methods, coda wave interferometry (CWI) and shear wave splitting (SWS) analysis to track stress related wave propagation effects during the waning phase of the 2002 NE fissure eruption at Mt Etna. CWI is used to estimate temporal changes in seismic wave velocity, while SWS is employed to monitor changes in elastic anisotropy. We analyse seismic doublets, detecting temporal changes both in wave velocities and anisotropy, consistent with observed eruptive activity. In particular, syn-eruptive wave propagation changes indicate a depressurization of the system, heralding the termination of the eruption, which occurs three days later.

Description: Published

Description: 1779-1788

Description: 1.4. TTC - Sorveglianza sismologica delle aree vulcaniche attive

Description: JCR Journal

Description: reserved

Description: Data assimilation is the combination of information from observations and models of a particular physical system in order to get the best possible estimate of the state of that system. The technique has wide applications across a range of earth sciences, a major application being the production of operational weather forecasts. Others include oceanography, atmospheric chemistry, climate studies, and hydrology. Data Assimilation for the Earth System is a comprehensive survey of both the theory of data assimilation and its application in a range of earth system sciences. Data assimilation is a key technique in the analysis of remote sensing observations and is thus particularly useful for those analysing the wealth of measurements from recent research satellites. This book is suitable for postgraduate students and those working on the application of data assimilation in meteorology, oceanography and other earth sciences.

Description: Preface. 1. Introduction; B. Boots, et al. Part I: Statistical models of spatial systems. Section A: Spatial statistics. 2. Geographic patterns of urban residential development; J. Lee. 3. Using local statistics for boundary characterization; B. Boots. 4. Local spatial interaction modelling based on the geographically weighted regression approach; T. Nakaya. Section B: Space-time analysis. 5. Understanding activity scheduling and rescheduling behaviour: theory and numerical illustration; Chang-Hyeon Joh, et al. 6. Geographical model of a self-organizing megalopolis with time-space convergence; I. Mizuno. 7. Epidemic modelling of HIV/AIDS transfers between eastern and western Europe; P. Smith, R. Thomas. Part II: Computational methods. Section A: Simulation models. 8. A spatial microsimulation model for social policy evaluation; D. Ballas, et al. 9. Analysis of the effect of land use patterns on the anthropogenic energy discharged from air conditioning and hot water supply using a modified CSU mesoscale model; T. Watanabe, et al. 10. Generalized Thuenen and Thuenen-Ricardo models for Asian land use; K. Konagaya. Section B: GIS models. 11. Balancing consensus and conflict with a GIS-based multi-participant, multi-criteria decision support tool; R. D. Feick, G. B. Hall. 12. Grid-based population distribution estimates from historical Japanese topographical maps using GIS: Y. Arai, S. Koike. 13. GIS modelling for rain-induced debris-flow hazards in a small watershed; S. Zhao, T. Tamura. Section C: The internet. 14. A geographical interpretation of cyberspace: preliminary analysis on the scaling tendency of information spaces; N. Shiode. 15. On modelling internet transactions as a time-dependent random walk: an application of the retail aggregate space-time trip (RASTT) model; R. G. V. Baker. 16. Development of disaster information network system in the Asian region: internet GIS for disaster information management; Y. Ogawa, et al. 17. Geographical conceptualization of cyberplaces; M. Takeyama.

Description: Foreword. How to climb the gravity wall; R. Rummel. I: Precise orbit determination and gravity field modelling. Strategies for precise orbit determination of low earth orbiters using the Global Positioning System; U. Hugentobler, G. Beutler. Aiming at a 1 cm orbit for low earth orbiters: reduced-dynamic and kinematic precise orbit determination; P. N. A. M. Visser, J. van den Ijssel. Space-wise, time-wise, torus and Rosborough representations in gravity field modelling; N. Sneeuw. Gravity field recovery from GRACE: unique aspects of the high precision inter-satellite data and analysis methods; G. Balmino. Global gravity field recovery using solely Global Positioning System tracking and accelerometer data from CHAMP; C. Reigber, et al. The processing of band-limited measurements: filtering techniques in the least squares context and in the presence of data gaps; W.-D. Schuh. II: Solid earth physics. Long wavelength sea level and solis surface perturbations driven by polar ice mass variations: fingerprinting Greenland and Antarctic ice sheet flux; M. E. Tamisiea, et al. Benefits from GOCE within solid earth geophysics; A. M. Marotta. The potential of GOCE in constraining the structure of the crust and lithosphere from post-glacial rebound; L. L. A. Vermeersen. Deep and shallow solid-earth structures reconstructed with sequential integrated inversion (SII) of seismic and gravity data; R. Tondi, et al. Present-day sea level change: observations and causes; A. Cazenave, et al. III: Ocean circulation. Global ocean data assimilation and geoid measurements; C. Wunsch, D. Stammer. Resolution needed for an adequate determination of the mean ocean circulation from altimetry and an improved geoid; C. Le Provost, M. Bremond. Error characteristics estimated from CHAMP, GRACE and GOCE derived geoids and from satellite altimetry derived mean dynamic topography; E. J. O. Schrama. Estimating the high-resolution mean sea-surface velocity field by combined use of altimeter and drifter data for geoid model improvement; S. Imawaki, et al. Combined use of altimetry and in situ gravity data for coastal dynamics studies; K. Haines, et al. Feasibility and contribution to ocean circulation studies of ocean bottom pressure determination; C. W. Hughes, V. Stepanov. Impact of geoid improvement on ocean mass and heat transport estimates; P. Le Grand. How operational oceanography can benefit from dynamic topography estimates as derived from altimetry and improved geoid; P. Y. Le Traon, et al. IV: Geodesy. Remarks on the role of height datum in altimetry-gravity boundary-value problems; F. Sacerdote, F. Sanso. Ocean tides in GRACE monthly averaged gravity fields; P. Knudsen. Tidal models in a new era of satellite gravimetry; R. D. Ray, et al. The elusive stationary geoid; M. Vermeer. Geodetic methods for calibration of GRACE and GOCE; J. Bouman, R. Koop. V: Sea level. Benefits of GRACE and GOCE to sea level studies; P. Woodworth, J. M. Gregory. What might GRACE contribute to studies of post glacial rebound? J. Wahr, I. Velicogna. Measuring the distribution of ocean mass using GRACE; R. S. Nerem, et al. Monitoring changes in continental water storage with GRACE; S. Swenson, J. Wahr. VI: Future concepts. Attitude and drag control: an application to the GOCE satellite; E. Canuto, et al. On superconductive gravity gradiometry in space; S. Zarembinski. Satellite-satellite laser links for future gravity missions; P. L. Bender et al. Possible future use of laser gravity gradiometers; P. L. Bender, et al. MICROSCOPE instrument development lessons for GOCE; P. Touboul. Needs and tools for future gravity measuring missions; M. Aguirre-Martinez, N. Sneeuw. VII: Closing session. GOCE: first earth explorer core mission; M. R. Drinkwater, et al. Earth gravity field from space from senors to earth sciences: closing remarks; G. Beutler.