bluuebunny/crossref_metadata_2025 huggingface dataset:
ShakeMaps during the Emilia sequence
Authors: Valentino Lauciani  , Licia Faenza  , Alberto Michelini
Published: June 2021

ShakeMap is a software package that can be used to generate maps of ground shaking for various peak ground motion (PGM) parameters, including peak ground acceleration (PGA), peak ground velocity, and spectral acceleration response at 0.3 s, 1.0 s and 3.0 s, and instrumentally derived intensities. ShakeMap has been implemented in Italy at the Istituto Nazionale di Geofisica e Vulcanologia (INGV; National Institute of Geophysics and Volcanology) since 2006 (http://shakemap.rm.ingv.it), with the primary aim being to help the Dipartimento della Protezione Civile (DPC; Civil Protection Department) civil defense agency in the definition of rapid and accurate information on where earthquake damage is located, to correctly direct rescue teams and to organize emergency responses. Based on the ShakeMap software package [Wald et al. 1999, Worden et al. 2010], which was developed by the U.S. Geological Survey (USGS), the INGV is constructing shake maps for Ml ≥3.0, with the adoption of a fully automatic procedure based on manually revised locations and magnitudes [Michelini et al. 2008]. The focus of this study is the description of the progressive generation of these shake maps for the sequence that struck the Emilia-Romagna Region in May 2012. […]
The role of radiation damping in the modeling of repeated earthquake events
Authors: Paola Crupi  , Andrea Bizzarri
Published: June 2021

We have investigated the role of the radiation damping term (RDT) on repeated earthquake ruptures by modeling the faulting process through a single one-dimensional analog fault system governed by different constitutive laws. The RDT expresses the energy lost by the seismic waves. The RDT is inherently accounted for in more elaborated, fully dynamic models of extended fault, whereas it is neglected in one-dimensional fault models. In this study, we adopt various formulations of the laboratory-derived rate-dependent and state-dependent friction constitutive laws: the Dieterich-Ruina law, the Ruina-Dieterich law and the Chester and Higgs law. Our numerical results clearly indicate that the RDT significantly affects the system dynamics. More specifically, the more the RDT is effective, the more frequent the slip failures are (with a cycle-time reduction of ca. 30%). We also show that inclusion of the RDT tends to promote smaller but more frequent earthquake instabilities, irrespective of the choice of the governing law. Our data shed light on the limitations implied by the conventional formulation of the equation of motion for the spring system, in which the energy radiation is ignored.
A statistical study on precursory effects of earthquakes observed through the atmospheric vertical electric field in northeast India
Authors: Abhijit Choudhury  , Anirban Guha  , Barin Kumar De  , Rakesh Roy
Published: June 2021

The study of anomalous variations in the near-surface atmospheric vertical electric field (VEF) that have the form of bay-like depressions in strength have been used as precursors of earthquakes in various studies. We present here the first statistical report from an earthquake-prone zone in northeast India from July 2009 to July 2012. The 10 days that were meteorologically fair and with earthquake occurrences were selected for the present analysis. The average VEF bay durations and depths were ca. 50 min to 70 min, with the corresponding magnitudes of 500 Vm-1 to 800 Vm-1. Anomalous variation in VEF before 7 to 12 hour of the impending earthquake has been observed. There was a 31% probability that a VEF bay would show as an earthquake precursor. The positive correlation coefficient was 0.72 between the VEF bay depth and the ratio of earthquake magnitude to depth, while the negative correlation coefficient of 0.82 was calculated between VEF bay duration and the ratio of earthquake magnitude to depth. There was moderate correlation for distance of the earthquake epicenter to the observation point with both VEF bay depth and VEF bay duration. The correlation of the time difference of VEF variations and earthquakes with VEF bay depth was good, whereas the correlation of the time difference of VEF variations and earthquakes with VEF bay duration was too low to be considered.
Seismic intensity assignments for the 2008 Andravida (NW Peloponnese, Greece) strike-slip event (June 8, Mw=6.4) based on the application of the Environmental Seismic Intensity scale (ESI 2007) and the European Macroseismic scale (EMS-98)
Authors: Spyridon D. Mavroulis  , Ioannis G. Fountoulis  , Emmanuel N. Skourtsos  , Efthymis L. Lekkas  , Ioannis D. Papanikolaou
Published: June 2021

On June 8, 2008, a strike-slip earthquake (Mw=6.4) was generated NE of the Andravida town (NW Peloponnese, western Greece) due to the activation of the previously unknown western Achaia strike-slip fault zone (WAFZ). Extensive structural damage and earthquake environmental effects (EEE) were induced in the NW Peloponnese, offering the opportunity to test and compare the ESI 2007 and the EMS-98 intensity scales in a moderate strike-slip event. No primary EEE were induced, while secondary EEE including seismic fractures, liquefaction phenomena, slope movements and hydrological anomalies were widely observed covering an area of about 800 km2. The lack of primary effects and the relatively small surface deformation with respect to the earthquake magnitude is due to the thick Gavrovo flysch layer in the affected area that isolated and absorbed the subsurface deformation from the surface. According to the application of the EMS-98 scale, damage to masonry buildings ranged from grade 3 to 5, while damage in most of R/C buildings ranged from grade 1 to 3. A maximum ESI 2007 intensity VIII-IX is recorded, while the maximum EMS-98 intensity is IX. For all the sites where intensity VIII has been recorded the ESI 2007 and the EMS-98 agree, but for others the ESI 2007 intensities values are lower by one or two degrees than the corresponding EMS-98 ones, as it is clearly concluded from the comparison of the produced isoseismals. An exception to this rule is the Valmi village, where considerable structural damage occurs (IXEMS-98) along with the lack of significant EEE (VESI 2007). This variability between the ESI 2007 and the EMS-98 intensity values is predominantly attributed to the vulnerability of old masonry buildings constructed with no seismic resistance design. Correlation of all existing data shows that the geological structure, the active tectonics, and the geotechnical characteristics of the alpine and post-alpine formations along with the construction type of buildings were of decisive importance in the damage and the EEE distribution.
Electron precipitation events in the lower ionosphere and the geospace conditions
Authors: José Henrique Fernandez  , Emília Correia
Published: June 2021

We present an analysis of localized ionospheric perturbations detected at Comandante Ferraz Brazilian Antarctic Station (McIlwain parameter L~2.25) as fast-amplitude variations of very low frequency (VLF) signals transmitted from Hawaii (NPM, at 21.4 kHz), also known as Trimpi events. The study covers the first six months of 2007, during the period of minimum activity in the 23rd solar cycle. The occurrence of Trimpi events in the Antarctica peninsula region was studied in association with solar-wind parameters in the neighborhood of the Earth (geospace), along with the geomagnetic activity level (Ap, Dst indices). The analysis shows that the Trimpi events occurred predominantly during geomagnetically disturbed periods, but they have a more intricate association with the geospace regimes. The events achieve higher occurrence during the recovery phase of some geomagnetic storms, and also show a close association with electron flux enhancements in the belt region, especially those with higher energy. The higher event incidence occurred a few hours after what we call the 'angle bracket' phenomenon: when the solar wind velocity rises simultaneous with a decrease in its density.
First Multi-GAS based characterisation of the Boiling Lake volcanic gas (Dominica, Lesser Antilles)
Authors: Rossella Di Napoli  , Alessandro Aiuppa  , Patrick Allard
Published: June 2021

We used a Multi-component Gas Analyser System (Multi-GAS) to measure, for the very first time, the composition (H2O, CO2, H2S, SO2) of the volcanic gas plume issuing from the Boiling Lake, a vigorously degassing, hot (T ~ 80-90°C) volcanic lake in Dominica, West Indies. The Multi-GAS captured in-plume concentrations of H2O, CO2 and H2S were well above those typical of ambient atmosphere, while no volcanic SO2 was detected (<0.05 ppm). These were used to derive the Boiling Lake plume characteristic ratios of CO2/H2S (5.2±0.4) and H2O/CO2 (31.4±6). Assuming that other volcanic gas species (e.g., HCl, CO, H2, N2, etc.) are absent in the plume, we recalculated a (air-free) composition for the sourcing volcanic gases of ~ 96.3% H2O, 3.1% CO2 and 0.6% H2S. This hydrous gas composition is within the range of published gas compositions in the Lesser Antilles region, and slightly more H2O-rich than obtained for the fumaroles of the nearby Valley of Desolation (~94.4% H2O, 4.7% CO2 and 0.8% H2S; CO2/H2S of ~5.7). We use our results, in tandem with the output of numerical simulations of gas scrubbing in the lake-water (performed via the EQ3/6 software), to derive new constraints on the degassing mechanisms at this poorly studied (but potentially hazardous) volcanic lake.
Results of the preparatory study “PREMIER Analysis of Campaign Data”
Authors: Elisa Castelli  , Samuele Del Bianco  , Bianca Maria Dinelli  , Daniel Gerber  , Hermann Oelhaf  , Wolfgang Woiwode  , Bärbel Vogel  , Björn-Martin Sinnhuber  , Roland Ruhnke  , Ugo Cortesi
Published: June 2021

The relevance of the UTLS (Upper Troposphere and Lower Stratosphere) region and the impact of limb emission
measurements at millimetre and sub-millimetre wavelengths for investigation of chemical, dynamical and
radiative processes occurring at these altitudes constitute a major focus of the atmospheric research activities
supported by the European Space Agency (ESA) in the last two decades.[...]
GRAPE, Solar Terrestrial Physics in an operational environment
Authors: Giorgiana De Franceschi  , Maurizio Candidi
Published: June 2021

[…] The collection of papers that forms this special issue represents the whole amplitude of research that is being conducted in the framework of GRAPE, while also connecting to other initiatives that address the same objectives in regions outside the polar regions, and worldwide, such as the Training Research and Applications Network to Support the Mitigation of Ionospheric Threats (TRANSMIT; www.transmitionosphere.net), a Seventh Framework Programme (FP7) Marie Curie Initial Training Network that is focused on the study of ionospheric phenomena and their effects on systems embedded in our daily life, Near-Earth Space Data Infrastructure for e-Science (ESPAS), an FP7-funded project that aims to provide the e-Infrastructure necessary to support the access to observations, for the modeling and prediction of the near-Earth Space environment, Concept for Ionospheric Scintillation Mitigation for Professional GNSS in Latin America (CIGALA) and its follow-up and extension Countering GNSS High-Accuracy Applications Limitations due to Ionospheric Disturbances in Brazil (CALIBRA), both of which are funded by the European Commission in the frame of FP7, for facing the equatorial ionosphere and its impact on GNSS. The main objective of the present Special Issue of Annals of Geophysics is to collect recent reports on work performed in the polar regions and on the datasets collected in time by the instrumentation deployed across various countries. This collection will set the starting point for further research in the field, especially in the perspective of the new and very advanced space system that will be available in the next few years. […]
Evidence of active tectonics in the Augusta Basin (eastern Sicily, Italy) by Chirp sub-bottom sonar investigation
Authors: Claudia Pirrotta  , Maria Serafina Barbano  , Daniela Pantosti  , Paolo Marco De Martini
Published: June 2021

A Chirp sub-bottom sonar investigation was performed in the 150 km2 wideAugustaBasin, located in the eastern Sicily Ionian coast, a region repeatedly hit by strong earthquakes in historical time, with the end of identifying possible evidence of active tectonics. Seismostratigraphy shows two main reflectors: R1, formed between 60 ka and 19 ka BP, and R2 that is the top of the Holocene deposits. Morphobathymetry reveals two marine abrasion surfaces, Ms1 and Ms2 that are related to the 35 ka and 25 ka BP marine high stills, respectively. This study highlights that R1 and the onlapping Holocene sediments are affected by normal and probably strike-slip faulting. A set of NE-SW striking normal faults represents the oldest system, because they dislocate R1 but not the Holocene deposit. NNW-SSE striking extensional faults show more recent activity since they displace Ms2, the Holocene sequence and cause seafloor up-warping. NE-SW normal faults produce asymmetric basins where the Holocene deposits form wedged bodies. ENE-WSW left-lateral faults dissect a paleo-island, Ms2 and the NNW-SSE fault system. Moreover, seismically induced  slumps involving the Holocene sediments, are found at the foot of some fault scarps. The presence of slumped bodies and active faults indicates ongoing deformation in the basin. Identified active faults are consistent with the main regional Malta Escarpment fault system, of which they can be considered as the incipient westernmost extension. This study supports the hypothesis that the Malta Escarpment is active and can be responsible for the regional seismicity.
Some remarks about lidar data preprocessing and different implementations of the gradient method for determining the aerosol layers
Authors: Federico Angelini  , Gian Paolo Gobbi
Published: June 2021

The determination of atmospheric aerosol layers from lidar returns is possible through automated algorithms. This product is useful, for example, in monitoring the Boundary Layer Height (BLH) as well as volcanic plumes. Aerosol layers are usually detected using the gradient method, i.e. by finding the inflection points of the range-corrected backscattered signal. These points can be either calculated as the minima of the numerical derivative of the signal, or by zero-order Digital Wavelet Transforms. Since for low signal-to-noise ratios the numerical derivative is very prone to noise-induced fluctuations, a moving average is often performed. We demonstrate why this procedure should be avoided in the gradient calculation. Finally, an alternative approach to the Digital Wavelet Transform is proposed, giving the same results but lowering the computational times by about one order of magnitude.
GPS time series at Campi Flegrei caldera (2000-2013)
Authors: Prospero De Martino  , Umberto Tammaro  , Francesco Obrizzo
Published: June 2021

The Campi Flegrei caldera is an active volcanic system associated to a high volcanic risk, and represents a well known and peculiar example of ground deformations (bradyseism), characterized by intense uplift periods, followed by subsidence phases with some episodic superimposed mini-uplifts. Ground deformation is an important volcanic precursor, and, its continuous monitoring, is one of the main tool for short time forecast of eruptive activity. This paper provides an overview of the continuous GPS monitoring of the Campi Flegrei caldera from January 2000 to July 2013, including network operations, data recording and processing, and data products. In this period the GPS time series allowed continuous and accurate tracking of ground deformation of the area. Seven main uplift episodes were detected, and during each uplift period, the recurrent horizontal displacement pattern, radial from the “caldera center”, suggests no significant change in deformation source geometry and location occurs. The complete archive of GPS time series at Campi Flegrei area is reported in the Supplementary materials. These data can be usefull for the scientific community in improving the research on Campi Flegrei caldera dynamic and hazard assessment.
A catalogue of non-tectonic earthquakes in central-eastern Italy
Authors: Marco Cattaneo  , Enrico Caffagni  , Simona Carannante  , Ezio D'Alema  , Massimo Frapiccini  , Chiara Ladina  , Simone Marzorati  , Giancarlo Monachesi
Published: June 2021

Quarry explosions and other non-tectonic signals can contaminate seismic catalogues, especially in areas where dense seismic networks allow to detect even low energy events. This paper presents the algorithm adopted for the discrimination of non-tectonic earthquakes in central-eastern Italy, an area with a high rate of events of this kind (4500 were recorded in the 1996-2012 period). Starting from an empirical classification based on the analysis of areas in which the ratio between daytime and nighttime events is strongly anomalous, a waveform similarity approach allows to simplify the procedure of detection making the final classification more robust. The resulting catalogue of non-tectonic earthquakes (quarry blasts and other anomalous signals) is a useful tool for anyone wanting to carry out a careful analysis of the tectonic seismicity of central-eastern Italy.
Latitudinal characteristics of GPS derived ionospheric TEC: a comparative study with IRI 2012 model
Authors: Monti Chakraborty  , Sanjay Kumar  , Barin Kumar De  , Anirban Guha
Published: June 2021

The present study investigates the variation of Total Electron Content (TEC) using Global Positioning System (GPS) satellites from four equatorial to mid-latitudes stations over a period of one year. The stations are Port Blair (11.63°N, 92.70°E), Agartala (23.75°N, 91.25°E), Lhasa (29.65°N, 91.10°E) and Urumqi (43.46°N, 87.16°E). The diurnal, monthly and seasonal variations of TEC have been explored to study its latitudinal characteristics. Analysis of TEC data from these stations reveals the characteristics of latitudinal variation of Equatorial Ionospheric Anomaly (EIA). To validate the latest IRI 2012 model, the monthly and seasonal variations of GPS-TEC at all the four stations have been compared with the model for three different topside options of electron density, namely, NeQuick, IRI-01-corr and IRI-2001. TEC predictions from IRI-2001 top side electron density option using IRI 2012 model overestimates the observed TEC especially at the low latitudes. TEC from IRI- NeQuick and IRI-01-corr options shows a tendency to underestimate the observed TEC during the day time particularly in low latitude region in the high solar activity period. The agreement between the model and observed values are reasonable in mid latitude regions. However, a discrepancy between IRI 2012 derived TEC with the ground based observations at low latitude regions is found. The discrepancy appears to be higher in low-latitude regions in comparison to mid latitude regions. It is concluded that largest discrepancy in TEC occur as a result of poor estimation of the hmF2 and foF2 from the coefficients.
The 2nd to 4th century explosive activity of Vesuvius: new data on the timing of the upward migration of the post-A.D. 79 magma chamber
Authors: Raffaello Cioni  , Claudia D’Oriano  , Antonella Bertagnini  , Daniele Andronico
Published: June 2021

We present volcanological data on the deposits of the Santa Maria Member (SMM), the eruption cycle occurred at Vesuvius (Italy) in the period between the A.D. 79 plinian and the A.D. 472 subplinan eruptions. Historical accounts report only sporadic, poorly reliable descriptions of the volcanic activity in this period, during which a stratified sequence of ash and lapilli beds, up to 150 cm thick, with a total volume estimated around 0.15 km3, was widely dispersed on the outer slopes of the volcano. Stratigraphic studies and component analyses suggest that activity was characterized by mixed hydromagmatic and magmatic processes. The eruption style has been interpreted as repeated alternations of continuous and prolonged ash emission activity intercalated with short-lived, violent strombolian phases. Analyses of the bulk rock composition reveal that during the entire eruption cycle, magma maintained an homogeneous phonotephritic composition. In addition, the general trends of major and trace elements depicted by the products of the A.D. 79 and A.D. 472 eruptions converge to the SMM composition, suggesting a common mafic end-member for these eruptions. The volatile content measured in pyroxene-hosted melt inclusions indicates two main values of crystallization pressures, around 220 and 70 MPa, roughly corresponding to the previously estimated depth of the magma reservoirs of the A.D. 79 and A.D. 472 eruptions, respectively. The study of SMM eruption cycle may thus contribute to understand the processes governing the volcano reawakening immediately after a plinian event, and the timing and modalities which govern the migration of the magma reservoir.
New insights into Mt. Vesuvius hydrothermal system and its dynamic based on a critical review of seismic tomography and geochemical features
Authors: Edoardo Del Pezzo  , Giovanni Chiodini  , Stefano Caliro  , Francesca Bianco  , Rosario Avino
Published: June 2021

The seismic velocity and attenuation tomography images, calculated inverting respectively P-wave travel times and amplitude spectra of local VT quakes at Mt. Vesuvius have been reviewed and graphically represented using a new software recently developed using Mathematica8TM. The 3-D plots of the interpolated velocity and attenuation fields obtained through this software evidence low-velocity volumes associated with high attenuation anomalies in the depth range from about 1 km to 3 km below the sea level. The heterogeneity in the distribution of the velocity and attenuation values increases in the volume centred around the crater axis and laterally extended about 4 km, where the geochemical interpretation of the data from fumarole emissions reveals the presence of a hydrothermal system with temperatures as high as 400-450°C roughly in the same depth range (1.5 km to 4 km). The zone where the hydrothermal system is space-confined possibly hosted the residual magma erupted by Mt. Vesuvius during the recent eruptions, and is the site where most of the seismic energy release has occurred since the last 1944 eruption.
Electric effects induced by artificial seismic sources at Somma-Vesuvius volcano
Authors: Rosa Di Maio  , Gianpaolo Cecere  , Prospero De Martino  , Ester Piegari
Published: June 2021

In this paper, we present a series of self-potential measurements at Somma-Vesuvius volcanic area acquired in conjunction with an active seismic tomography survey. The aim of our study is both to provide further confirmation to the occurrence of seismo-electric coupling and to identify sites suitable for self-potential signal monitoring at Somma-Vesuvius district. The data, which were collected along two perpendicular dipoles, show significant changes on the natural electric field pattern. These variations, attributable to electrokinetic processes triggered by the artificial seismic waves, were observed after explosions occurred at a distance less than 5 km from the SP dipole arrays. In particular, we found that the NW-SE component of the natural electric field was more sensible to the shots than the NE-SW one, and the major effects did not correspond to the nearest shots. Such evidences were interpreted considering the underground electrical properties as deduced by previous detailed resistivity and self-potential surveys performed in the study area.
Eruption products of the 1883 eruption of Krakatau and their final settlement
Authors: Izumi Yokoyama
Published: June 2021

Firstly the volume of pyroclastic ejecta during the 1883 eruption of Krakatau is re-examined. To revise the volume of flow deposits, the author basically follows Verbeek’s observation while to estimate the fall deposits, as the last resort, the author assumes that volume ratios fall / flow are common to similar caldera eruptions, and the ratios determined by the caldera- forming eruptions of Novarupta and Pinatubo are applied to the Krakatau eruption. Verbeek’s estimation of the total volume of ejecta, 12 km3 is revised to 19 km3. This is significantly different from the volume of disrupted volcano edifice, 8 km3. Such a result does not support the predecessors’ hypothesis that calderas are formed by collapses of volcano edifices into magma reservoirs in replacement of the total ejecta. Through the discussion on the volume estimation of volcanic ejecta on and around Krakatau, the author recognizes that such estimation should be originally very difficult to attain enough accuracy. Much importance of “caldera deposits” to post-eruption settlements of the ejecta is emphasized. In relation to caldera formation, mechanical stability of a cavity in the crust is discussed. Lastly, upon the basis of subsurface structure, especially caldera deposits, a structural image of Krakatau caldera is presented.
Rake rotation introduces ambiguity in the formulation of slip-dependent constitutive models: slip modulus or slip path?
Authors: Andrea Bizzarri
Published: June 2021

The linear slip–weakening (SW) law, predicting that the traction decreases for increasing fault slip, is one of the most widely adopted governing models to describe the traction evolution and the stress release processes occurring during coseismic slip failures. We will show that, contrary to other constitutive models, the SW law inherently poses the problem of considering the Euclidean norm of the slip vector or its cumulative value along its path. In other words, it has the intrinsic problem of its analytical formulation, which does not have a solution a priori. By considering a fully dynamic, spontaneous, 3–D rupture problem, with rake rotation allowed, in this paper we explore whether these two formulations can lead to different results. We prove that, for homogeneous configurations, the two formulations give the same results, with a normalized difference less than 1%, which is comparable to the numerical error due to grid dispersion. In particular, we show that the total slip, the resulting seismic moment, the fracture energy density, the slip–weakening curve and the energy flux at the rupture front are practically identical in the two formulations. These findings contribute to reconcile the results presented in previous papers, where the two formulations have been differently employed. However, this coincidence is not the rule. Indeed, by considering models with a highly heterogeneous initial shear stress distribution, where the rake variation is significant, we have also demonstrated that the overall rupture history is quite different by assuming the two formulations, as well as the fault striations, the traction evolution and the scalar seismic moment. In this case the choice of the analytical formulation of the governing law does really matter.
Intercomparison of Metop-A SO2 measure- ments during the 2010- 2011 Icelandic eruptions
Authors: Maria Elissavet Koukouli  , Lieven Clarisse  , Elisa Carboni  , Jeroen van Gent  , Claudia Spinetti  , Dimitris Balis  , Spiros Dimopoulos  , Don Grainger  , Nicolas Theys  , Lucia Tampellini  , Claus Zehner
Published: June 2021

The European Space Agency project Satellite Monitoring of Ash and Sulphur Dioxide for the mitigation of Aviation Hazards, was introduced after the eruption of the Icelandic volcano Eyjafjallajökull in the spring of 2010 to facilitate the development of an optimal End-to-End System for Volcanic Ash Plume Monitoring and Prediction. The Eyjafjallajökull plume drifted towards Europe and caused major disruptions of European air traffic for several weeks affecting the everyday life of millions of people. The limitations in the volcanic plume monitoring and prediction capabilities gave birth to this observational system which is based on comprehensive satellite-derived ash plume and sulphur dioxide [SO2] level estimates, as well as a widespread validation using supplementary satellite, aircraft and ground-based measurements. The validation of volcanic total column SO2 measured by GOME-2/MetopA and IASI/MetopA are shown before, during and after the Eyjafjallajökull 2010 eruptions as well as for the 2011 Grimsvötn eruption. Co-located ground-based Brewer Spectrophotometer data extracted from the World Ozone and Ultraviolet Radiation Data Centre are also compared to the different satellite estimates
Crust and upper mantle velocity structure of the northwestern Indian Peninsular Shield from inter-station phase velocities of Rayleigh and Love waves
Authors: Gaddale Suresh  , Sankar N. Bhattacharya  , Satbir S. Teotia
Published: June 2021

We measure the inter-station Rayleigh and Love wave phase velocities across the northwestern Indian Peninsular shield (NW-IP) through cross-correlation and invert these velocities to evaluate the underneath crust and upper mantle velocity structure down to 400 km. We consider a cluster of three stations in the northern tip of the Peninsula and another cluster of eight stations in the south. We measure phase velocities along 28 paths for Rayleigh waves and 17 paths for Love waves joining two stations with one from each cluster and using broadband records of earthquakes which lie nearly on the great circle joining the pair of stations. The phase velocities are in the period range of 10 to 275 s for Rayleigh waves and of 10 to 120 s for Love waves. The isotropic model obtained through inversion of the phase velocities indicates 199.1 km thick lithosphere with 3-layered crust of thickness 36.3 km; the top two layers have nearly same velocities and both constitute the upper crust with thickness of 12.6 km. The upper crust is mafic, whereas the lower crust is felsic. In the mantle lid, velocities increase with depth. The velocities of mantle lid beneath NW-IP is lower than those beneath south Indian Peninsula showing the former is hotter than the later perhaps due to large Phanerozoic impact on NW-IP. The significant upper mantle low velocity zone beneath NW-IP indicates high temperature which could be attributed to the past existence of a broad plume head at the west-central part of the Peninsula.
Building monitoring in Bishkek and Dushanbe by the use of ambient vibration analysis
Authors: Bojana Petrovic  , Dino Bindi  , Marco Pilz  , Matteo Serio  , Sagynbek Orunbaev  , Jafar Niyazov  , Farhad Hakimov  , Pulat Yasunov  , Ulugbek T. Begaliev  , Stefano Parolai
Published: June 2021

Within the framework of the EMCA - Earthquake Model Central Asia - project, the cities of Bishkek (Kyrgyzstan) and Dushanbe (Tajikistan) were selected for building monitoring using measurements of seismic noise to obtain the dynamical properties of the buildings. Eight buildings of different construction types, date of construction and building height, both, Soviet-era and recently constructed buildings, were instrumented for a period of a few hours. In this study, an overview of the experiment is given, including a short description of each monitored building’s structure and the performed installation. Preliminary results for a representative Soviet-era residential building in Dushanbe are presented. Modal analysis is performed using the Frequency Domain Decomposition (FDD) method to estimate the natural frequencies and the mode shapes. The wave propagation velocities in the two directions along the building axes are determined by an interferometric approach. Although the experimental set-up was not the optimal, valuable information about the dynamical characteristics of the buildings were still obtained.
Probabilistic seismic hazard assessment of Bishkek, Kyrgyzstan, considering empirically estimated site effects
Authors: Shahid Ullah  , Dino Bindi  , Marco Pilz  , Stefano Parolai
Published: June 2021

It is well known that variability in the surface geology potentially leads to the modification of earthquake-induced ground motion over short distances. Although this effect is of major importance when seismic hazard is assessed at the urban level, it is very often not appropriately accounted for. In this paper, we present a first attempt at taking into account the influence of the shallow geological structure on the seismic hazard assessment for Bishkek, Kyrgyzstan, using a proxy (Vs30) that has been estimated from in situ seismic noise array analyses, and considering response spectral ratios calculated by analyzing a series of earthquake recordings of a temporary seismic network. To highlight the spatial variability of the observed ground motion, the obtained results are compared with those estimated assuming a homogeneous Vs30 value over the whole urban area. The seismic hazard is evaluated in terms of peak ground acceleration (PGA) and spectral acceleration (SA) at different periods (frequencies). The presented results consider the values obtained for a 10% probability of exceedance in 50 years. The largest SA estimated considering a rock site classification of the area (0.43 g) is observed for a period of 0.1 s (10 Hz), while the maximum PGA reaches 0.21 g. When site effects are included through the Vs30 proxy in the seismic hazard calculation, the largest SA, 0.67 g, is obtained for a period of 0.3 s (about 3.3 Hz). In terms of PGA, in this case the largest estimated value reaches 0.31 g in the northern part of the town. When the variability of ground motion is accounted for through response spectrum ratios, the largest SA reaches a value as high as 1.39 g at a period of 0.5 s. In general, considering site effects in the seismic hazard assessment of Bishkek leads to an increase of seismic hazard in the north of the city, which is thus identified as the most hazardous part within the study area and which is more far away from the faults.
A climatological morphology of ionospheric disturbances at high and polar latitudes
Authors: Dimitris N. Fotiadis  , Sotiria D. Matta  , Stamatis S. Kouris
Published: June 2021

After a historical introduction on the first well-documented observations of ionospheric phenomena and a review of the current, state-of-the art polar ionospheric studies, a climatological morphology of the irregular F-region plasma structures at high and polar latitudes is being presented, following a feature-aided pattern recognition method. Using the available in three solar cycles hourly foF2 data from 18 ionosonde stations, an ionospheric definition of disturbed conditions, independent of any causative mechanism, is being applied and positive/negative disturbances of duration smaller than 24 hours are sorted out. No latitudinal/longitudinal bins or seasons are defined and disturbances in each month and station are handled separately while four local time intervals of storm commencement are considered, according to solar zenith angle. A median profile per disturbance is produced only when a minimum occurrence probability is satisfied. Non-systematic features are excluded from this analysis by careful selection of the time window under morphological investigation. First, the median profiles of disturbance patterns are fitted to standard distributions and then, if they fail, they are grouped according to their major characteristic features and are described by a dynamic variation envelope along with their distribution in space and time. The present model, while being a non-conditional stand-alone model of ionospheric storms at high and polar latitudes offered to radio users, may complement existing empirical models. Finally, the present model may ultimately reveal cause-effect relationships with geomagnetic field or interplanetary parameters after further correlation studies undertaken in the future.
Early warning of tsunami from seismo-ionospheric fluctuation after Japan’s March 11, 2011, M=9.0 Tohoku earthquake using two-dimensional principal component analysis
Authors: Jyh-Woei Lin
Published: June 2021

Two-dimensional principal component analysis (2DPCA) is implemented to analyze the total electron content (TEC) anomalies after Japan’s Tohoku earthquake that occurred at 05:46 on March 11, 2011 (UTC) (Mw=9). 2DPCA and TEC data processing were conducted just after this devastating earthquake. Analysis results show an earthquake-associated TEC anomaly near the epicenter that began at 05:47. This may represent an extension of the precursor of the earthquake, to the precursor of China’s Wenchuan earthquake on May 12, 2008, detected by the study of Lin [2012], for which the data were obtained at a height of 150-200 km by the FORMOSAT-3 satellite system. It is impossible that such precursor caused by the acoustic shock waves. Another TEC anomaly near the epicenter occurred at 05:53, and this initiated the propagation of the tsunami effect related to the ionosphere through the acoustic shock waves from the epicenter. However, the TEC anomalies did not appear to be affected by a contemporaneous geomagnetic storm and other non-earthquake effects. The propagation of anomalous fluctuation could be an early warning of the tsunami for the regions far from the epicenter as it began to propagate with the higher speed of 3960-4950 km/h than the tsunami speed (720-800 km/h).

 
The 2009 L’Aquila earthquake coseismic rupture: open issues and new insights from 3D finite element inversion of GPS, InSAR and strong motion data
Authors: Manuela Volpe  , Simone Atzori  , Antonio Piersanti  , Daniele Melini
Published: June 2021

We present a Finite Element inverse analysis of the static deformation field for the Mw= 6.3, 2009 L’Aquila earthquake, in order to infer the rupture slip distribution on the fault plane. An univocal solution for the rupture slip distribution has not been reached yet with negative impact for reliable hazard scenarios in a densely populated area. In this study, Finite Element computed Green’s functions were implemented in a linear joint inversion scheme of geodetic (GPS and InSAR) and seismological (strong motion) coseismic deformation data. In order to fully exploit the informative power of our dense dataset and to honor the complexities of the real Earth, we implemented an optimized source model, represented by a fault plane subdivided in variable size patches, embedded in a high-resolution realistic three-dimensional model of the Apenninic seismo-tectonic setting, accounting for topographic reliefs and rheological heterogeneities deduced from local tomography. We infer that the investigated inversion domain contains two minima configurations in the solution space, i.e. a single- and a double-patch slip distribution, which are almost equivalent, so that the available datasets and numerical models are not able to univocally discriminate between them. Nevertheless our findings suggest that a two high-slip patch pattern is slightly favoured.
Acoustic 2D full waveform inversion to solve gas cloud challenges
Authors: Srichand Prajapati  , Deva Ghosh
Published: June 2021

The existing conventional inversion algorithm does not provide satisfactory results due to the complexity of propagated wavefield though the gas cloud. Acoustic full waveform inversion has been developed and applied to a realistic synthetic offshore shallow gas cloud feature with Student-t approach, with and without simultaneous sources encoding. As a modeling operator, we implemented the grid based finite-difference method in frequency domain using second order elastic wave equation. Jacobin operator and its adjoint provide a necessary platform for solving full waveform inversion problem in a reduced Hessian matrix. We invert gas cloud model in 5 frequency band selected from 1 to 12 Hz, each band contains 3 frequencies. The inversion results are highly sensitive to the misfit. The model allows better convergence and recovery of amplitude losses. This approach gives better resolution then the existing least-squares approach. In this paper, we implement the full waveform inversion for low frequency model with minimum number of iteration providing a better resolution of inversion results.
GPS tomography tests for DInSAR applications on Mt. Etna
Authors: Massimo Aranzulla  , Giuseppe Puglisi
Published: June 2021

Tropospheric artifacts of SAR images in a volcanic area like Mt. Etna cause ambiguity in the interpretation of deformations with such technique. It would be useful to measure the delay caused by tropospheric anomalies in synthetic aperture radar (SAR) satellite signals (phase of the back-scattered radar wave) that could be interpreted as deformation. From the delay estimated through the GPS data processing, the tropospheric tomography of electromagnetic waves refractivity, has been performed using the SIMULps12 software. The aim of this study was to perform software synthetic tests by using SIMULps12 applied to atmospheric tomography and to verify the influence of the different GPS geodetic network configurations on obtaining a reliable tomography. Three different anomalies of increasing complexity have been investigated in order to understand the representative parameters of a correct tomography, the best spatial resolution and the portions of space in which the tomography is reliable. The tests also focused on fixing/establishing the a-priori atmospheric model and the critical values of the main parameters involved in the tomographic inversion. To this end, we made a random choice of two days, necessary to define the tomographic problem. Three different network configurations with 15, 30 and 90 GPS receivers were studied. The results indicate that the well-resolved area of tomographic images increases with the number of GPS receivers not linearly, and that the actual GPS network of 42 receivers is capable of revealing/detecting the atmospheric anomalies.
Estimate of ULF electromagnetic noise caused by a fluid flow during seismic or volcano activity
Authors: Vadim V. Surkov  , Vyacheslav A. Pilipenko
Published: June 2021

The elaboration of theoretical models, even oversimplified, capable to estimate an expected electromagnetic effect during earthquake preparation process is not less important than the advancement of observational technique to detect seismic-related electromagnetic perturbations. Here possible mechanisms of ULF electromagnetic noise associated with seismic or volcanic activity are discussed. The electrokinetic (EK) and magnetohydrodynamic (MHD) effects due to an irregular flow of conducting rock fluid or magma flow are being revised. The conventional theory of EK effect in a water-saturated rock has been advanced by consideration of elliptic-shaped channels. A contribution of both mechanisms to observed ULF signal on the ground is shown to be dependent on the pore channel size/rock permeability. Estimates of magnetic and electrotelluric perturbations caused by magma motion along a volcano throat indicate on the important role of the surrounding rock conductivity. These estimates have proven that the mechanisms under consideration are able to generate ULF electromagnetic perturbations which could be detected by modern magnetometers under favorable conditions.
Accelerated ice-sheet mass loss in Antarctica from 18-year satellite laser ranging measurements
Authors: Shuanggen Jin  , Mosta Abd-Elbaky  , Guping Feng
Published: June 2021

Accurate estimate of the ice-sheet mass balance in Antarctic is very difficult due to complex ice sheet condition and sparse in situ measurements. In this paper, the low-degree gravity field coefficients of up to degree and order 5 derived from Satellite Laser Ranging (SLR) measurements are used to determine the ice mass variations in Antarctica for the period 1993–2011. Results show that the ice mass is losing with -36±13 Gt/y in Antarctica, -42±11 Gt/y in the West Antarctica and 6±10 Gt/y in the East Antarctica from 1993 to 2011. The ice mass variations from the SLR 5×5 have a good agreement with the GRACE 5×5, GRACE 5×5 (1&2) and GRACE (60×60) for the entire continent since 2003, but degree 5 from SLR is not sufficient to quantify ice losses in West and East Antarctica, respectively. The rate of ice loss in Antarctica is -28±17 Gt/y for 1993-2002 and -55±17 Gt/y for 2003-2011, indicating significant accelerated ice mass losses since 2003. Furthermore, the results from SLR are comparable with GRACE measurements.
Estimation of gravity noise variance and signal covariance parameters in least squares collocation with considering data resolution
Authors: Wojciech Jarmołowski
Published: June 2021

The article describes an implementation of the negative log-likelihood function in the determination of uncorrelated noise standard deviation together with the parameters of spherical signal covariance model in least squares collocation (LSC) of gravity anomalies. The correctness and effectiveness of restricted maximum likelihood (REML) estimates are fully validated by leave-one-out validation (LOO). These two complementary methods give an opportunity to inspect the parametrization of the signal and uncorrelated noise in details and can provide some guidance related to the estimation of individual parameters. The study provides the practical proof that noise variance is related with the data resolution, which is often neglected and the information on a priori noise variance is based on the measurement error. The data have been downloaded from U.S. terrestrial gravity database and resampled to enable an analysis with four different horizontal resolutions. These data are intentionally the same, as in the previous study of the same author, with the application of the planar covariance model. The aim is to compare the results from two different covariance models, which have different covariance approximation at larger distances. The most interesting outputs from this study confirm previous observations on the relations of the data resolution, a priori noise variance, signal spectrum and LSC accuracy.
Influence of fracture orientation distribution function on the estimates of gas-hydrate saturation of site 10 at Krishna-Godavari Basin, India
Authors: Yudhvir Singh  , Rajesh R. Nair
Published: June 2021

We estimate the gas-hydrate saturation in fractured reservoirs of gas hydrate-rich marine sediments from Krishna-Godavari basin along the eastern margin of India. Effective medium modeling (EMM) is a combination of self-consistent approximation (SCA), differential effective medium (DEM) modeling and smoothing and it deals with the anisotropy associated with clay platelets’ orientation. It proves to be a good choice attributable to its dependency on physical parameters alone. Previous approaches appertain to the implementation of orientation distribution function (ODF) on clay platelets alone assuming a vertical ellipsoidal shape of gas hydrates whilst in the present study, we have implemented ODF on hydrate bearing fractures assigning an ellipsoidal shape to them as well. A bias of ~2-4% in the saturation estimates apparently streamlines the betterness of our method.