Waveform inversion

Intraplate earthquakes are ongoing activity in the Kachchh region. The area is seismically active and falls in Zone V of the seismic Zoning Map of India. The devastating Bhuj (Kachchh) Earthquake of MS 7.6 occurred in this zone on 26 th January, 2001 causing severe damage to civil engineering structures and loss of human life. The surface manifestations of deformation of this earthquake include fractures/ fissures, lateral spread, slump, subsidence, upheaval, sand blows and craters. Bhuj Earthquake has caused considerable damage to earth dams lying in isoseist VIII and above in Kachchh. Damages to dams are in the form of longitudinal and transverse cracks, differential settlement, slumps/ slide, displacements and in some cases leakage. A review of the available geological, seismological and geotechnical data have been done to asses the impact of Bhuj Earthquake and subsequent seismic events in the area on ground deformation and engineering structures. Main cause of the ground deformation and damage is liquefaction of the soil under seismic shaking. Tectonic influence on the development of fissures/ cracks on the ground as well as on the earth dams has been observed.

Summary Here we present an example of a refraction and reflection FWI case study, from offshore Norway, using various minimization norms, in order to obtain reliable and robust parameter models to address deep imaging challenges associated with sill intrusions and hydrothermal vents. Significant improvement is obtained using a flow involving five variants of FWI.

Gravity data from Iceland and its surroundings are analysed and modelled with respect to seismic data. A Bouguer gravity map of Iceland is recomputed based on admittance between the topography and the gravity and with corrections for glacial ice sheets. From seismic data and with the help of relations between the residual topography and the depth to seismic boundaries we construct maps of the main seismic boundaries, including the Moho. By inversion calculations we recomputed these maps, assuming different density values for Seismic Layer 4 to fit the observed gravity field. We found that the average density of Layer 4 has to be in the range 3050-3150 kg m -3 in order to fit both seismic and gravity data. Thus we conclude that Layer 4 is a transition zone between the mantle and the oceanic crust in Iceland. Furthermore by assuming that the upper-mantle density variations necessary to compensate for the gravity effect of crustal layers, are caused by thermal variations in the upper mantle, we calculate the depth to the 1200 • C isotherm to be at 30-50 km depth below Iceland but rising up to less than 20 km below parts of the volcanic zone in Northern Iceland. We conclude that the temperature within the Seismic Layer 4 is close to 600 • C at its top, increasing to approximately 950 • C at its bottom (Moho), which makes a widespread layer of partially molten material within Layer 4 unlikely. By use of cross spectral analysis of the gravity field and the external topographic load at short wavelengths, we conclude that the elastic plate thickness in Iceland can hardly exceed 6 km. In addition we point out that the residual isostatic anomalies have circular forms east of the eastern volcanic zone but are near parallel to the ridge axis on the western side. This form of the anomalies may be caused by pressure from the eastward moving mantle plume below the eastern volcanic zone.

Los grandes sismos en la zona de subducción de México presentan, en ocasiones, agrupamientos espacio-temporales. Ha sido sugerido que dichos agrupamientos pueden ser debidos a la interacción de esfuerzos entre estos eventos. En este trabajo se investiga esta posibilidad mediante el cálculo del cambio en los esfuerzos de Coulomb cosísmicos producidos por siete grandes eventos de subducción (Mw>7.4), ocurridos en una secuencia entre 1973 y 1985 en la placa de Cocos y entre 1995 y 2003 en la placa de Rivera, ambas subducentes bajo la placa de Norte-América. Dichos cálculos están basados en las distribuciones de deslizamientos obtenidas, para estos sismos, mediante previas inversiones cinemáticas. Los cambios de esfuerzos calculados son superpuestos acumulativamente en función del tiempo y el espacio. Los resultados muestran que dichos eventos pueden estar relacionados unos con otros y que, al menos una parte de dicha relación, podría ser atribuida al incremento en los esfuerzos cosísmicos debido a la ocurrencia de grantes eventos previos en zonas adyacentes. Palabras clave: Sismología, esfuerzos sísmicos, distribución de esfuerzos, convergencia de placas, zona de subducción.

The lithosphere of the South American continent has been studied little, especially in northern Brazil (the Amazonian region). A 3D lithospheric S-velocity model of South America was obtained by first carrying out Rayleigh and Love wave groupvelocity tomography, and then inverting the regionalized dispersion curves. Fundamental mode group velocities were measured using a Multiple Filtering Technique. More than 12,000 paths were examined and about 6000 Rayleigh-and 3500 Love-wave dispersion curves with good quality were retrieved. Checkerboard tests showed that our dataset permits the resolution of features 400-800 km across laterally in the central part of the continent from crustal to upper mantle depths. Our results confirm previous tomographic results and correlate well with the major geological provinces of South America. The 3D S-velocity model confirms both regional features of SE Brazil from P-wave travel-time tomography and continental-scale features of central and western South America from waveform inversion, e.g., lowest velocities in the Andean upper mantle; three parts of the Nazca plate with flat subduction; strong low-velocity anomalies in the upper-mantle depth beneath the Chaco basin. Furthermore, our 3D model revealed new features in the South American continent: (1) high velocities in the lower crust were consistently found in regions with high Bouguer or free-air anomalies; (2) the NE-SW trending TransBrasiliano shear zone was delineated by a NE-SW low-velocity belt at lithospheric depths; (3) the eastern Amazonian craton appears to have thicker lithosphere than the western craton; (4) in areas of Archean nuclei located in the northeastern Guaporé shield and southeastern São Francisco craton, high velocity anomalies were found down to 150 km.

The paper reviews the results of GPR surveying for determining old cement concrete slabs location under asphalt concrete pavement on section of the Highway М-2 “Crimea” in the Moscow Region of the Russian Federation. For survey the GPR technical equipment was used (“Logis” Ltd, Ramenskoe), that is the antenna assembly with the central frequency radiation of 1700 MHz and the maximum sounding depth up to 0,8 m. The works were held in October 2012 on wet road surface under damp weather conditions.

Two great underthrusting earthquakes that occurred along the coast of Peru in 2001 and 2007 involve spatiotemporal slip distributions that differ from the predominantly unilateral or bilateral rupture expansion of many great events. Commonly used finite-source rupture model parameterizations, with specified rupture velocity and/or short duration of slip at each grid point applied to the seismic data for these two events, lead to incorrect slip-distributions or inaccurate estimation of rupture velocities as a result of intrinsic kinematic constraints imposed on the model slip distributions. Guided by large aperture array back projections of teleseismic broadband P-wave signals that image slip locations without imposing a priori kinematic constraints on the rupture process, we exploit the availability of large global broadband body and surface wave data sets to consider the effects of varying the kinematic constraints in teleseismic finite-source waveform inversions. By allowing longer than usual rupture durations at each point on the fault using a flexible subfault source-time function parameterization, we find that the anomalous attributes of the 2001 and 2007 Peru earthquake ruptures are readily recognized and accounted for by compound rupture models. The great 23 June 2001 (M w 8:4) earthquake involved an initial modestsize event that appears to have triggered a much larger secondary event about 120 km away that developed an overall slip distribution with significant slip located back along the megathrust in the vicinity of the initial rupture. The great 15 August 2007 (M w 8:0) earthquake was also a composite event, with a modest size initial rupture followed by a 60-sec delayed larger rupture that initiated ∼50-60 km away and spread up-dip and bilaterally. When back projections indicate greater rupture complexity than captured in a simple slip-pulse-type rupture model, one should allow for possible long-subfault slip-duration or composite triggered sequences, and not overly constrain the earthquake slip distribution. Online Material: Figures of waveform fits and animations of back projections, accumulating slip, and moment-rate history.

In this study, an integrated multi-channel analysis of Surface Waves (MASW) technique is applied to explore the geotechnical parameters of subsurface layers at the Zafarana wind farm. Moreover, a seismic hazard procedure based on the extended deterministic technique is used to estimate the seismic hazard load for the investigated area. The study area includes many active fault systems along the Gulf of Suez that cause many moderate and large earthquakes. Overall, the seismic activity of the area has recently become better understood following the use of new waveform inversion method and software to develop accurate focal mechanism solutions for recent recorded earthquakes around the studied area. These earthquakes resulted in major stress-drops in the Eastern desert and the Gulf of Suez area. These findings have helped to reshape the understanding of the seismotectonic environment of the Gulf of Suez area, which is a perplexing tectonic domain. Based on the collected new information and data, this study uses an extended deterministic approach to reexamine the seismic hazard for the Gulf of Suez region, particularly the wind turbine towers at Zafarana Wind Farm and its vicinity. Alternate seismic source and magnitudefrequency relationships were combined with various indigenous attenuation relationships, adapted within a logic tree formulation, to quantify and project the regional exposure on a set of hazard maps. We select two desired exceedance probabilities (10 and 20 %) that any of the applied scenarios may exceed the largest median ground acceleration. The ground motion was calculated at 50th, 84th percentile levels for both selected probabilities of exceeding the median.

There are several subduction systems near the Japanese islands. The 2011 Mw9.0 Tohoku-oki megathrust earthquake occurred at the northeastern Japan subduction zone and revealed a complementary relation between the slip areas for huge earthquakes and small repeating earthquakes (REs). Investigations of REs in other subduction zones and their comparison with Tohoku area are important for revealing generation mechanism of megathrust earthquakes. We use seismograms from the High Sensitivity Seismograph Network (Hi-net) and Japan Meteorological Agency (JMA)’s permanent seismograph stations from 8 May 2003 to 31 December 2012. We detect RE along the Izu-Bonin and Ryukyu trenches, using similarity of seismogram pairs. Although, Igarashi (2010) and Yamashita et al. (2012) have already examined RE activity in this region, we mainly follow the method of Uchida et al. (2010) to compare with the REs at Tohoku area. In the method, pair with coherence larger than 0.95 at multiple stations is consi...

The Gulf of Aqaba is one of the most active places around Egypt, with several earthquake sequences having occurred there through ancient and modern times. In the last century, four earthquake sequences took place in the gulf (1983, 1990, 1993, and 1995). Recently, on 27 June 2015, a sequence of 96 earthquakes with local magnitudes ranging from 0.7 to 5.2 was recorded by the Egyptian National Seismological Network (ENSN). On 16 May 2016, another earthquake sequence started and continued for several consecutive days, with 95 events with local magnitudes ranging from 1.6 to 5.5 being centered south of the 27 June 2015 sequence. In this paper, we analyse the complete waveform and polarity data set of both earthquake sequences to determine their focal mechanisms and to update our knowledge of the stress field in the Gulf of Aqaba. Through the results obtained, we conclude that, the Gulf of Aqaba is affected by a primary structure of a left-lateral strike-slip fault with a minor normal component in most segments. Our study also infers the presence of a secondary structure, which is indicated to be a right-lateral strike-slip with a minor reverse component.

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We use a two-stage nonlinear technique to invert strong motions records and geodetic data to retrieve the rupture history of an earthquake on a finite fault. The unknown model parameters, spatially variable peak slip velocity, slip direction, rupture time and rise time, are given at the vertices of subfaults, whereas the parameters within a subfault can vary through a bilinear interpolation of the vertex values. The forward modeling is performed with a discrete wavenumber technique, whose Green's functions include the complete response of the vertically varying non-attenuating Earth structure. The GPS coseismic data are compared with the synthetic displacements using a L2 norm, while the recorded and modeled waveforms are compared in the frequency domain, using a cost function that is a hybrid representation between L1 and L2 norms. During the first stage (search), an algorithm based on heat-bath simulated annealing generates an ensemble of models that efficiently sample the goo...

ABSTRACTPore pressure in sediments beneath salt in the Gulf of Mexico varies widely creating a potentially dangerous and difficult drilling challenge. Estimating elastic parameters of sediments beneath salt is key to the prediction of pore pressure and reducing the drilling risk in exiting the base of the salt. In this paper we investigate the ability of 2D waveform inversion to recover the elastic parameters in the sedimentary layer beneath the salt from a walk‐away VSP (vertical seismic profile) carried out with the receivers in the salt, with the objective of estimating pore pressure at the base of the salt (to be estimated using traditional methods). We propose an effective method for performing the inversion and apply this method to a blind test of a large and realistic synthetic dataset. To facilitate the design of a VSP survey suitable to this type of inversion we also present an analysis into the effects of the receiver array receiver spacing. It is shown that the resulting ...

ABSTRACTPore pressure in sediments beneath salt in the Gulf of Mexico varies widely creating a potentially dangerous and difficult drilling challenge. Estimating elastic parameters of sediments beneath salt is key to the prediction of pore pressure and reducing the drilling risk in exiting the base of the salt. In this paper we investigate the ability of 2D waveform inversion to recover the elastic parameters in the sedimentary layer beneath the salt from a walk‐away VSP (vertical seismic profile) carried out with the receivers in the salt, with the objective of estimating pore pressure at the base of the salt (to be estimated using traditional methods). We propose an effective method for performing the inversion and apply this method to a blind test of a large and realistic synthetic dataset. To facilitate the design of a VSP survey suitable to this type of inversion we also present an analysis into the effects of the receiver array receiver spacing. It is shown that the resulting ...

An all-optical inverter using transverse-mode switching of a 1.55-m vertical-cavity surface-emitting laser is demonstrated. When an external light is injected to a first high-order mode, the output power of the fundamental mode is strongly suppressed due to injection locking resulting in a large extinction ratio of over 20 dB. Waveform inversion is demonstrated for the input signal of a 5-GHz sinusoidal wave.

Source parameters for 40 earthquakes with epicentres in the Aegean Sea and the surrounding lands have been determined using P and SH body waveform inversion of digital waveforms from the Global Seismograph Network (GSN). These results are combined with 145 previous solutions, 41 of which were determined by first motion polarities and 104 by waveform modelling. Thus, a new updated database of source parameters for earthquakes for the period 1953-1999 is available. These fault plane solutions confirm our previous knowledge about the seismotectonics of the Aegean Sea and the surrounding lands. They also provide strong evidence that the western part of the Peloponnese (Gulf of Patras to Gulf of Kyparissia) is mainly deforming by strike-slip faulting, parallel in strike to the Cephalonia Fault and are in favour of the models that suggest a connection of the North Anatolian Fault (NAF) zone with the transform zone of the Ionian Islands. The sedimentary arc (inner part of the Hellenic trench) is deforming by normal faulting with the Taxes trending $ E-W. We did not determine any fault plane solutions at the eastern part of the Hellenic arc indicating pure strike-slip motions as expected from the presence of the Pliny and Strabo trenches. However, we did determine solutions that indicate normal faulting combined with a considerable strike-slip component. In the central Aegean Sea the newly determined focal mechanisms support the conclusion that the area, extending from the eastern coasts of Evia up to the coasts of Turkey, is exhibiting a clear strike-slip character. Thus, the effect of the propagating tip of the North Anatolian fault into the Aegean is very clearly pronounced. The focal mechanisms in the back-arc Aegean area confirm the existence of normal faulting with Taxes trending NNE-SSW in western Anatolia and NNW-SSE in Greece. A zone showing NNE-SSW extension that runs parallel to Northern Aegean branch of the NAF zone up to the Corinth Gulf is depicted from the mechanisms of few earthquakes.

The Trans-Mexican Volcanic Belt (TMVB) is oblique to the subduction zone. Background seismicity is very low. Nevertheless, two large instrumental earthquakes were recorded: the 1912 Acambay (M w 6.9) and the 1920 Jalapa (M w 6.4) earthquakes. Macroseismic data were systematically searched for crustal earthquakes on the TMVB contained in historical accounts. The macroseismic reports were inverted for the best fitting magnitude and epicenter. The western end of the TMVB shows the highest level of seismic activity. An earthquake is reported in 1568 (M w 7.2 ± 0.2) and a second large event took place in 1875 (M w 7.0 ± 0.2). Two other earthquakes are reported in the western TMVB in 1611 and 1749 (M w 6.4). The 1858 earthquake (M w 7.6 ± 0.3), in the central TMVB occurred on faults located to the west of the 1912 Acambay event. The eastern TMVB is less active. An earthquake in 1575 (M w 5.7) occurred east of the city of Puebla. The 1887 (M w 6.2 ± 0.2) and the 1920 Jalapa earthquakes are the larger events in this region. The seismicity observed from the instrumental and historical seismicity catalogs show that active tectonic deformation occurs throughout the TMVB and that it is not confined to specific regions where instrumental earthquakes have been located and active faults mapped. The number of large earthquakes in the TMVB, suggest unique large-scale deformation of this complex volcanic belt. The presence of large earthquakes in this tectonic province, where 40% of the population of Mexico live, underlines the importance of reevaluating hazard in this densely populated region. Plain Language Summary The subduction of an oceanic plate results in the creation of a volcanic arc that is normally parallel to the coastline, where the subduction process takes place. In the case of the Trans-Mexican Volcanic Belt (TMVB), its orientation is unique: It is oblique to the subduction zone to the south. Also, many active geological faults are distributed throughout the volcanic belt. The presence of these faults suggests that the TMVB is geologically active and under continuous deformation, albeit at a slow rate. Earthquakes are rarely recorded in the TMVB. However, in the last 500 years of written history, there is clear evidence of very large earthquakes that occurred on these faults. Some of these earthquakes are apparently as large as magnitude 7.3. During the past five centuries, at least seven earthquakes larger than magnitude 6.5 have taken place in these shallow geological faults in the crust of the TMVB. The presence of these earthquakes is evidence that the TMVB is under extension, in a manner which is not observed in other volcanic arcs. These earthquakes also occur near the more important population centers, posing an important seismic hazard that frequently is not taken into account.

The Trans‐Mexican Volcanic Belt (TMVB) is oblique to the subduction zone. Background seismicity is very low. Nevertheless, two large instrumental earthquakes were recorded: the 1912 Acambay (Mw 6.9) and the 1920 Jalapa (Mw 6.4) earthquakes. Macroseismic data were systematically searched for crustal earthquakes on the TMVB contained in historical accounts. The macroseismic reports were inverted for the best fitting magnitude and epicenter. The western end of the TMVB shows the highest level of seismic activity. An earthquake is reported in 1568 (Mw 7.2 ± 0.2) and a second large event took place in 1875 (Mw 7.0 ± 0.2). Two other earthquakes are reported in the western TMVB in 1611 and 1749 (Mw 6.4). The 1858 earthquake (Mw 7.6 ± 0.3), in the central TMVB occurred on faults located to the west of the 1912 Acambay event. The eastern TMVB is less active. An earthquake in 1575 (Mw 5.7) occurred east of the city of Puebla. The 1887 (Mw 6.2 ± 0.2) and the 1920 Jalapa earthquakes are the lar...

We analyze seismic and acoustic data from a series of controlled truck bomb explosions to develop scaling laws and functional relations between charge size and various waveform properties. The explosions had yields of 3-12 ‫ן‬ 10 3 kg trinitrotoluene (TNT), and the receivers were placed at distances of 1-16 km, so the data mimic the data previously recorded from actual terrorist truck bombings. We examine four airblast properties (peak overpressure, impulse per unit area, pulse duration, and average shock velocity) and three seismic properties (peak displacement of P wave, low-frequency asymptote of displacement spectrum, and the corner frequency of displacement spectrum) as potential yield estimators. Impulse per unit area and pulse duration observations prove to be the most robust yield indicators; however, peak overpressure, peak displacement, and low-frequency spectral asymptote have significant utility as well. The acoustic scaling laws are more portable than the seismic scaling laws because regional differences in atmospheric structure can be well described by pressure and temperature observations, while regional differences in geologic structure are dependent on a large number of less accessible parameters. We apply the scaling laws developed here to seismic waveforms of the 1998 Nairobi bombing and find a yield of 2.0-6.0 ‫ן‬ 10 3 kg TNT. This value is consistent with but more precise than a previous estimate made via a time domain waveform inversion. Additional testing indicates that our functional relations are likely applicable to surface chemical explosions in general and not limited solely to truck bombs.

Reservoirs with vertically aligned fractures can be represented equivalently by HTI (horizontal transverse isotropy) media. But inverting for the anisotropic parameters of HTI media is a challenging inverse problem, because of difficulties inherent in a multiple parameter inversion. In this paper, when we invert for the anisotropic parameters, we consider for the first time the azimuthal rotation of a two-dimensional seismic survey line from the symmetry of HTI. The established wave equations for the HTI media with azimuthal rotation consist of nine elastic coefficients, expressed in terms of five modified Thomsen parameters. The latter are parallel to the Thomsen parameters for describing velocity characteristics of weak VTI (vertical transverse isotropy) media. We analyze the sensitivity differences of the five modified Thomsen parameters from their radiation patterns, and attempt to balance the magnitude and sensitivity differences between the parameters through normalization and tuning factors which help to update the model parameters properly. We demonstrate an effective inversion strategy by inverting velocity parameters in the first stage and updates the five modified Thomsen parameters simultaneously in the second stage, for generating reliably reconstructed models.

The 26th January 2001 Bhuj earthquake was followed by intense aftershock activity. Aftershock data from United States Geological Survey (USGS) utilized in this study encompasses three months period from 26th January to 26th April 2001. Epicenters of the aftershock are plotted on a map depicting active faults. All the aftershocks of magnitude > 5 and 70% of those ranging between magnitude 3 and 5 are confined to an area resembling a horseshoe pattern with a pointed end towards NE. The other 20% of magnitude 3 to 5 are enclosed within an almost parallel boundary. Only 10% are found to be beyond this limiting boundary. 50% of the recorded aftershocks took place within the first week of the main event and this study reveals that the basic characteristic pattern of aftershock activity can be determined on the basis of the data of only one week. Four major NW-SE trending active faults are mapped in the Kutch region. They define the western limit of Cambay structure and also mark the western limit of Dharangadhra and Wadhwan basins along the SE continuation in Saurashtra. These faults separate the Kutch region into two geologically different blocks. On the SW side the mapped horseshoe pattern gets characteristically truncated along the western most fault, which is characterized by a strike-slip movement in the south and vertical movement in the north. The present study has revealed that the epicenter of the 26th January earthquake is located in the vicinity of the Bhachau township, close to the intersection with the Kutch mainland fault. Furthermore, it has been noticed that most of the epicenters of the aftershock are confined in the intersectional area of the Kutch mainland fault and the NW-SE faults.

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We have analyzed 44 micro-earthquakes with magnitudes between 1.2 and 3.4, which occurred in the Dobrá Voda area, Slovakia, in the period 2001-2009. The epicentres of the micro-earthquakes form a cluster elongated in the ENE-WSW direction. This direction coincides with the orientation of the main fault systems in the area: Dobrá Voda and Brezová faults. The depths of the hypocentres vary from 1 km to 14 km. Three different methods were used to calculate the focal mechanisms: (a) a method using the polarities of Pg and Pn waves, (b) the P-wave amplitude inversion of moment tensors, and (c) the waveform inversion of moment tensors. The majority of the analyzed micro-earthquakes have a left-lateral strike-slip focal mechanism with weak normal or reverse components. The full moment tensors comprise significant nondouble-couple (non-DC) components. The non-DC components are partly numerical errors of the inversion but might be also of a physical origin. The most accurate values of the non-DC components are obtained from the P-wave amplitude inversion. For this inversion, the isotropic component (ISO) and the compensated linear vector dipole component (CLVD) are mostly positive and well correlated. This might indicate tensile faulting. Adopting the model of tensile faulting, we estimated the mean ratio of P to S wave velocities in the focal area from the values of ISO and CLVD, v P /v S = 1.5-1.6. The three different datasets of the focal mechanisms have been inverted for the present-day tectonic stress in the Dobrá Voda area. The slip shear stress component criterion was applied in the stress inversion. The results of the three inversions are wellconsistent and point to a high reliability and good accuracy of the inverted stress. The orientations of the principal stresses are (azimuth/plunge): σ 1 =210-220°/5-25°, σ 2 = 70-105°/55-75°, and σ 3 = 305-315°/ 15-25°, and the shape ratio is R = 0.45-0.60. The azimuth is measured clockwise from the north and the plunge downwards from the horizontal plane. The retrieved maximum compression lies along the belt of the Malé Karpaty Mts. The local tectonic stress reflects complex tectonic conditions in the area. The presence of tensile faulting might point to an extensional stress regime in the area.

A right-lateral shear zone in the San-in region, southwest Japan, has been proposed by previous geological and seismological studies. It locates 350 km north of the Nankai Trough, that is, the main plate boundary between the subducting Philippine Sea and overriding Amurian plates and presumably accommodates a part of the relative plate motion. We present a geodetic evidence of the proposed shear zone using GNSS velocity data. Distinct shear deformation is identified only between ~132.5°E and ~135°E along a coastline which is a part of the proposed shear zone, and we propose to call the geodetically identified shear zone as the San-in shear zone (SSZ). The SSZ is a concentrated deformation zone with a width of ~50 km and can be modeled by a deep creep on a vertical strike slip fault with a creep rate of ~5 mm/year. There are some active faults parallel and oblique to the overall trend of the SSZ, but no single active fault coincides with the SSZ. Lineaments of microseismicity and source faults of large earthquakes are almost oriented in NNW-SSE in the SSZ and oblique to the overall trend of the SSZ. They are interpreted as conjugate Riedel shears. Based on these geodetic, seismological, and geomorphological observations, we suggest that the SSZ is a developing and young shear zone in a geological time scale.

Recovering physical properties such as attenuation and velocity of the Earth's heterogeneities is as important as recovering the shape and the surface reflectivity of the heterogeneities themselves. A reliable estimate of attenuation in the Earth is necessary to improve our knowledge of subsurface physical properties like the degree of fluid saturation. Moreover the attenuation may also be relevant to 'bright spot' studies in reservoir characterization. Within this context, this paper presents applications of asymptotic viscoacoustic waveform inversion to synthetic and ultrasonic laboratory data recorded to characterize the velocity and attenuation of a lava sample collected on the Vesuvius volcano. The waveform inversion method is based on a combination of ray theory and the Born approximation to linearize the relation between the scattered wavefield and the velocity and attenuation perturbation models. The iterative linearized inverse problem is solved using the classic least-squares criterion. Asymptotic local analysis of the Hessian operator published in a previous paper by Ribodetti et al. showed the theoretical uncoupling between the velocity and attenuation parameters. The method is first applied to realistic and calibrated synthetic data computed using the discrete boundary integral wavenumber method. The reliability of decoupling between the velocity and attenuation parameters during the inversion is confirmed through two case studies corresponding to a local velocity heterogeneity without any associated attenuation perturbation and a local attenuation heterogeneity without any associated velocity perturbation, respectively. Second, the method is applied to an ultrasonic laboratory data set that was recorded to determine the velocity and attenuation of a tephrite rock sample collected on the Vesuvius volcano. A velocity of 3200 m s −1 and an attenuation factor of 480 were found, which are consistent with the geological nature of the analysed sample. The numerical tests presented in this paper validate former theoretical development of asymptotic waveform inversion for characterization of viscoacoustic media. Application to ultrasonic data confirms that the proposed method can be used for reliable estimations of the velocity and attenuation properties of rock from laboratory experiments. Comparable methodology can be extended for use with data from multichannel seismic reflection surveys, providing an opportunity to compare results of laboratory and field experiments.

The present study presents the analysis of a moderate earthquake (Mw 4.0) and its largest aftershocks located along the Red Sea coast, southwestern Saudi Arabia, with the aim to understand the enigma of peculiar seismicity in the Arabian Shield. We analyzed a high-quality waveform dataset collected from ten well-recorded earthquakes of moment magnitude ranging from 2.0 to 4.0 in order to determine the hypocenter locations and focal mechanisms. The focal mechanisms were retrieved from the regional moment-tensor inversion for the mainshock and using the P-wave polarities for the corresponding aftershocks of Mw ≥ 2.0, respectively. The focal mechanism solutions were inverted to retrieve the seismogenic stress using the stress tensor inversion. The combination of the nearby fault trends and the obtained results from hypocentral relocations, focal mechanism solutions, and stress tensor inversion emphasizes that the NE fault trend is likely to be the causative fault resulting in the 2017 ...

The southern San Jacinto fault zone is characterized by high seismicity and a complex fault pattern that offers an excellent setting for investigating interactions between distinct faults. This fault zone is roughly outlined by two subparallel master fault strands, the Coyote Creek and Clark‐San Felipe Hills faults, that are located 2 to 10 km apart and are intersected by a series of secondary cross faults. Seismicity is intense on both master faults and secondary cross faults in the southern San Jacinto fault zone. The seismicity on the two master strands occurs primarily below 10 km; the upper 10 km of the master faults are now mostly quiescent and appear to rupture mainly or solely in large earthquakes. Our results also indicate that a considerable portion of recent background activity near the April 9, 1968, Borrego Mountain rupture zone (ML=6.4) is located on secondary faults outside the fault zone. We name and describe the Palm Wash fault, a very active secondary structure loc...

The Bartin earthquake of September 3. 1968 is the strongest instrumentally recorded earthquake to occur along the Black Sea margin in northwestern Turkey. The source mechanism of the Bartin earthquake, as determined in this study from long period P wave first motions and from the inversion of P and SH waves, indicates thrust faulting with a strike of 28", dip of 38" and rake of 80'. The average (centroid) depth is 4 km and the seismic moment is 3.9 x 1O25 dyn cm. The Bartin earthquake provides the first evidence for active thrust faulting at the southern margin of the Black Sea. The Black Sea has probably evolved as a back-arc basin resulting from the northward subduction of Tethys. Seismicity, fault plane solutions, and other geophysical data suggest that at the present time the Black Sea is closing under north-south compression.

We have determined the source mechanisms (double‐couple orientation, moment, centroid depth, source time function) of 14 earthquakes on the northern Mid‐Atlantic Ridge (0°–72°N) from an inversion of long‐period P and SH waveforms. The earthquakes are all characterized by nearly pure normal faulting on fault planes that dip at about 45° and strike parallel to the local trend of the ridge axis. Moments range from 3 to 15×1024 dyn cm, and the source time functions are all of simple form. The P and S waveforms for all earthquakes can be well matched using conventional values for t* (1 and 4 s, respectively). These earthquakes are all very shallow; centroid depths range between 1.2 and 3.1 km beneath the seafloor. The P waves from these earthquakes show strong water column reverberations, suggesting that fault rupture extended to the seafloor. The predominant period of these reverberations constrains the water depth in the epicentral region. On the basis of estimated water depth and epic...

Teleseismic body waves from large earthquakes are used to study the downdip geometry of continental normal faults in the Aegean. Waveform modeling techniques together with rigorous statistical tests are applied to put firm bounds on the amount of downdip curvature of these faults and the role of coseismic slip on a basal detachment. Synthetic modeling shows that good azimuthal station coverage and inclusion of SH waves are necessary to resolve fault curvature. The data indicate ruptures of the Aegean events occurred on planar faults extending across the entire brittle portion of the crust. No seismogenic low‐angle detachment faulting at the base of the upper crust was detected for these events. Decoupling of the brittle upper crust from the plastic lower crust probably occurs aseismically in a ductile fashion.

A sequence of small earthquakes occurred in Central Mexico, at the northern edge of the Trans-Mexican Volcanic Belt (TMVB) in the State of Queretaro, during the first 3 months of 1998. Medium to large events in the continental regime of central Mexico are not common, but the seismic history of the region demonstrates that faults there are capable of generating destructive events. The sequence was analyzed using data from a temporary network with the goals of identifying the causative fault and its relation to regional tectonics. Employing a waveform inversion scheme adapted from a method used for regional studies, we found that the source mechanisms conform to the style of faulting (i.e. extension in the E -W direction) representative of the Taxco -San Miguel Allende Fault system. This system has been proposed as the southernmost extension of the Basin and Range (BR) Province. The spatial distribution of hypocenters and source mechanisms indicate that the seismogenic segment was a fault with an azimuth of approximately 334j with almost pure dip slip. Since events which occurred just south from this region show features which are consistent with TMVB tectonics (i.e. extension in an N -S direction), the sequence may mark the boundary between the TMVB and BR stress domains.

The southern San Jacinto fault zone is characterized by high seismicity and a complex fault pattern that offers an excellent setting for investigating interactions between distinct faults. This fault zone is roughly outlined by two subparallel master fault strands, the Coyote Creek and Clark‐San Felipe Hills faults, that are located 2 to 10 km apart and are intersected by a series of secondary cross faults. Seismicity is intense on both master faults and secondary cross faults in the southern San Jacinto fault zone. The seismicity on the two master strands occurs primarily below 10 km; the upper 10 km of the master faults are now mostly quiescent and appear to rupture mainly or solely in large earthquakes. Our results also indicate that a considerable portion of recent background activity near the April 9, 1968, Borrego Mountain rupture zone (ML=6.4) is located on secondary faults outside the fault zone. We name and describe the Palm Wash fault, a very active secondary structure loc...

Teleseismic body waves from large earthquakes are used to study the downdip geometry of continental normal faults in the Aegean. Waveform modeling techniques together with rigorous statistical tests are applied to put firm bounds on the amount of downdip curvature of these faults and the role of coseismic slip on a basal detachment. Synthetic modeling shows that good azimuthal station coverage and inclusion of SH waves are necessary to resolve fault curvature. The data indicate ruptures of the Aegean events occurred on planar faults extending across the entire brittle portion of the crust. No seismogenic low‐angle detachment faulting at the base of the upper crust was detected for these events. Decoupling of the brittle upper crust from the plastic lower crust probably occurs aseismically in a ductile fashion.

We present a stochastic inversion procedure for common-offset ground-penetrating radar (GPR) reflection measurements. Stochastic realizations of subsurface properties that offer an acceptable fit to GPR data are generated via simulated annealing optimization. The realizations are conditioned to borehole porosity measurements available along the GPR profile, or equivalent measurements of another petrophysical property that can be related to the dielectric permittivity, as well as to geostatistical parameters derived from the borehole logs and the processed GPR image. Validation of our inversion procedure is performed on a pertinent synthetic data set and indicates that the proposed method is capable of reliably recovering strongly heterogeneous porosity structures associated with surficial alluvial aquifers. This finding is largely corroborated through application of the methodology to field measurements from the Boise

Study of source parameters of small to moderate and large earthquakes is important to under-stand the differences and similarities between dynamic ruptures of different earthquakes and cla-rifying the scaling relations. In the present study, we have characterized source parameters and presented new and revised empirical relationships between various source parameters for Kachchh region of Gujarat, India to facilitate to draw first-order conclusions regarding the trends in the region. We have studied total 202 aftershocks of shallow-focus (hypo central depth less than 40 km) and moderate magnitude recorded over the Kachchh region during January 2001 to De-cember 2012 by different seismological observatories of India Meteorological Department. We have adopted the spectral technique for source parameter estimation, where S-wave displacement spectra are considered and applied Fast Fourier Transform (FFT) to compute displacement spec-tra. We have followed the Brune’s source model for our...

Study of source parameters of small to moderate and large earthquakes is important to understand the differences and similarities between dynamic ruptures of different earthquakes and clarifying the scaling relations. In the present study, we have characterized source parameters and presented new and revised empirical relationships between various source parameters for Kachchh region of Gujarat, India to facilitate to draw first-order conclusions regarding the trends in the region. We have studied total 202 aftershocks of shallow-focus (hypo central depth less than 40 km) and moderate magnitude recorded over the Kachchh region during January 2001 to December 2012 by different seismological observatories of India Meteorological Department. We have adopted the spectral technique for source parameter estimation, where S-wave displacement spectra are considered and applied Fast Fourier Transform (FFT) to compute displacement spectra. We have followed the Brune's source model for our estimation and the estimated values of source parameters show close approximation to the global values. While derived empirical relations between different source parameters, they demonstrate direct or inverse proportion to linear or power scale. Interrelation between seismic moment, rupture parameters, corner frequency and radiated seismic energy can be summarized as 2.94 0 c M f − ∝ ,

The east coast of the Tohoku district, Japan has a high seismicity, including aftershocks of the 2011 M9 Tohoku earthquake. We analyzed 1142 earthquakes with$$4.4 \le M_{W} \le 5.0$$4.4≤MW≤5.0that occurred in 2003 through 2018 and obtained spatio-temporal pattern of stress drop on the Pacific Plate that subducts beneath the Okhotsk Plate. Here we show that small earthquakes at edges of a region with a large slip during the 2011 Tohoku earthquake had high values of stress drop, indicating that the areas had a high frictional strength and suppressed the coseismic slip of the 2011 Tohoku earthquake. In addition, stress drops of small earthquakes in some of the areas likely decreased after the 2011 Tohoku earthquake. This indicates that the frictional strength decreased at the areas due to the following aftershocks of the 2011 Tohoku earthquake, consistent with a high aftershock activity. This also supports that the frictional properties on a subducting plate interface can be monitored ...

In this research, multi-configuration electromagnetic induction (EMI) measurements were conducted in a corn field to estimate variation in soil electrical conductivity profiles in the roots zone. Electromagnetic forward model based on the full solution of Maxwell's equation was used to simulate the apparent electrical conductivity measured with EMI system (the CMD mini-Explorer). Joint inversion of multiconfiguration EMI measurements were performed to estimate the vertical soil electrical conductivity profiles. The inversion minimizes the misfit between the measured and modeled soil apparent electrical conductivity by DiffeRential Evolution Adaptive Metropolis (DREAM) algorithm, which is based on Bayesain approach. Results indicate that soil electrical conductivity profiles have low values close to the corn plants, which indicates loss of soil moisture due to the root water uptake. These results offer valuable insights into future potential and emerging challenges in the development of joint analysis of multi-configuration EMI measurements to retrieve effective soil electrical conductivity profiles.

Extension of permanent seismic networks is usually governed by a number of technical, economic, logistic, and other factors. Planned upgrade of the network can be justified by theoretical assessment of the network capability in terms of reliable estimation of the key earthquake parameters (e.g., location and focal mechanisms). It could be useful not only for scientific purposes but also as a concrete proof during the process of acquisition of the funding needed for upgrade and operation of the network. Moreover, the theoretical assessment can also identify the configuration where no improvement can be achieved with additional stations, establishing a tradeoff between the improvement and additional expenses. This paper presents suggestion of a combination of suitable methods and their application to the Little Carpathians local seismic network (Slovakia, Central Europe) monitoring epicentral zone important from the point of seismic hazard. Three configurations of the network are considered: 13 stations existing before 2011, 3 stations already added in 2011, and 7 new planned stations. Theoretical errors of the relative location are estimated by a new method, specifically developed in this paper. The resolvability of focal mechanisms determined by waveform inversion is analyzed by a recent approach based on 6D moment-tensor error ellipsoids. We consider potential seismic events situated anywhere in the studied region, thus enabling Bmapping^of the expected errors. Results clearly demonstrate that the network extension remarkably decreases the errors, mainly in the planned 23-station configuration. The already made three-station extension of the network in 2011 allowed for a few real data examples. Free software made available by the authors enables similar application in any other existing or planned networks. Keywords Seismic network. Relative location uncertainty. Focal-mechanism uncertainty. Waveform inversion. Uncertainty mapping. Weak earthquakes. Little Carpathians 1 Introduction Little Carpathians (L.C.) belong to the seismically most active zones on the territory of Slovakia. In spite currently observed weak events (Fig. 1), remarkable historical seismicity has been documented in this region. The

Tsunami observations play an important role in resolving offshore earthquake slip distributions. Nondispersive shallow-water models are often used with a static initial sea surface pulse derived from seafloor deformation in computation of tsunami Green's functions. We compare this conventional approach with more advanced techniques based on a dispersive model with a static initial sea surface pulse and with the surface waves generated from kinematic seafloor deformation. These three sets of tsunami Green's functions are implemented in finite-fault inversions with and without seismic and geodetic data for the 2010 Mentawai M w 7.8 tsunami earthquake. Seafloor excitation and wave dispersion produce more spread-out waveforms in the Green's functions leading to larger slip with more compact distribution through the inversions. The fit to the recorded tsunami and the deduced seismic moment, which reflects the displaced water volume, are relatively insensitive to the approach used for computing Green's functions.

The earth structure between C052198B, and observatory stations in Australia has been investigated through analysis in the time domain seismograms are constructed from an earth model, the CMT solution of the earthquake and station location method, and the corner frequency is set at 20 mHz. station instruments responses, the measured and synthetic seismogram compared with the same units. The seismogram comparison indicates discre pancies between recorded data anisotropic PREM model wave, as well as the S and core reflected ScS and ScS Discrepancies of Love wave travel time and explained by changes gradient of  h in the upper mantle. While for Rayleigh wave body waves, corrections to the zero order coefficients of the mantle. The interpretation strong anisotropy in the upper mantle. The anisotropy also occur extent, at layers beneath the upper mantle

On October 8th, 2010, a 5.0 m b earthquake with intensity VI (MM) occurred close to Mara Rosa, in the North of Goi as State, central Brazil, in an area where previous low magnitude seismicity had been observed. This earthquake was felt up to 300 km away from the epicenter, and was the biggest event ever detected in Central Brazil Seismic Zone. Despite the difficulty of associating earthquakes in Stable Continental Interior with geological structures, this event is possibly related to the reactivation of a geological fault of the continental-scale Transbrasiliano Lineament (TBL): the aftershock activity observed with an 8-station seismic network, indicates a NW dipping, SW-NE trending reverse fault, parallel to the TBL. The P axis is NW-SE oriented, consistent with expected stress direction in the region. Cross correlation technique was used to synchronize the weak P-and S-wave phases of some of the aftershocks, recorded at regional stations, with the corresponding arrivals of the main shock producing a consistent set of relative arrival times. The use of regional station corrections allowed the mainshock to be located with uncertainties small enough to qualify for a GT5 event, which will help to constrain 3D velocity models in South America. We found that the aftershocks were distributed around a circular area about 1.5e2.0 km across, with no events in the middle. This is interpreted as the mainshock rupture completely releasing all stresses. The rupture area and the mainshock moment correspond to a stress-drop of about 2 MPa.

We performed a 3D seismic tomography study of the northwest Alborz region in Iran, by inversion of P-wave arrival times of nearly 250 local earthquakes recorded at 13 permanent stations between 2006 and 2010. We applied the simultaneous inversion code SIMULPS14 carefully tuned to data set by choice of optimal regularization parameters. Resolution tests with synthetic data show that the inversion results are well constrained around the North Tabriz Fault (NTF) from 3 to 16 km depth. In this depth range, our results show a series of anomalies with relatively high and low velocity, reflecting the heterogeneous geology of northwest Alborz and generally correlating well with local changes of rock types at the surface across this section of the NTF. The boundary surface between the distinct velocity anomalies is generally consistent with the NTF strike. The high and low velocity anomalies at 5-14 km depth parallel to the surface expression of the NTF are interpreted as basaltic volcanic rocks in the south and Mesozoic sedimentary and basement rocks in the north. In addition, cross sections show a significant change in dip of the NTF in the southeastern part, from nearly vertical in the NW to about 60°dip toward SE.