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The crust of the South American platform recorded imprints of dynamic processes related with the opening of the Central and South Atlantic but has not been well measured. Crustal structure can be retrieved from teleseismic receiver functions using H – κ stacking, but nearly parallel stripes of high stacking values existing in stacking images for seismic stations in sedimentary area cause difficulties in identifying solutions. We show that some seemingly spurious stripes that do not point to any layer solution are helpful in the identification of the solution position. With the aid of the auxiliary stripes, we retrieved thicknesses and Vp / Vs of sedimentary and crystalline crust for 65 permanent stations of the Brazilian Seismographic Network and six new portable seismic stations in Brazil and Uruguay. The resulted sedimentary thickness and Vp / Vs exhibit a good correlation with the Phanerozoic sediments in the South American basins. The crust of Paraná–Etendeka Large Igneous Province (LIP) had been expected to be more mafic since it had ever been penetrated by mantle magma in the Cretaceous related to the south Atlantic opening. However, we found very low Vp / Vs (1.67) in the crystalline crust beneath the LIP, implying a more felsic crust and that no significant mafic intruding/underplating has occurred in the region. The more felsic crust may be formed in a special evolution early than the magmatic event, or during the magmatic event by releasing crustal volatiles. The resulted sedimentary thickness and Vp / Vs ratios exhibit a good correlation with the Phanerozoic sediments in the South American basins, which implies that Triassic–Jurassic and Cretaceous magmatism did not cause significant metamorphism in sediments formed before the magmatic events. [ABSTRACT FROM AUTHOR]

Backazimuthal variations in the shear wave splitting of core-refracted shear waves (SKS, SKKS and PKS phases, jointly referred to as X KS) at the Black Forest Observatory (BFO, Southwest Germany) indicate small-scale lateral and partly vertical variations of the seismic anisotropy. However, existing anisotropy studies and models for the nearby Upper Rhine Graben (URG) area in the northern Alpine foreland are mostly based on short-term recordings and by this suffer from a limited backazimuthal coverage and averaging over a wide or the whole backazimuth range. To identify and delimit laterally confined anisotropy regimes in this region, we carry out X KS splitting measurements at six neighbouring (semi-)permanent broad-band seismological recording stations (interstation distance 10–80 km). We manually analyse long-term (partly > 20 yr) recordings to achieve a sufficient backazimuthal coverage to resolve complex anisotropy. The splitting parameters (fast polarization direction |$\phi $|⁠ , delay time |$\delta t$|⁠) are determined in a single- and multi-event analysis. We test structural anisotropy models with one layer with horizontal or tilted symmetry axis and with two layers with horizontal symmetry axes (transverse isotropy). To account for lateral variations around a single recording site, modelling is compared for the whole and for limited backazimuth ranges. Based on this, we provide a 3-D block model with spatial variation of anisotropic properties. Based on delay times > 0.3 s and missing discrepancies between SKS and SKKS phases, which do not support lower mantle anisotropy, the found anisotropy is placed in the lithosphere and asthenosphere. The spatial distribution as well as the lateral and backazimuthal variations of the splitting parameters confirm lateral and partly vertical variations in anisotropy. On the east side of the URG, we suggest two anisotropic layers in the Moldanubian Zone (south) and one anisotropic layer in the Saxothuringian Zone (north). In the Moldanubian Zone, a change of the fast polarization directions is observed between the east and the west side of the URG, indicating different textures. At the boundary between the two terranes, an inclined anisotropy is modelled which may be related with deformation during Variscan subduction. Regarding the observation of numerous null measurements and inconsistent splitting parameters, especially (southwest of BFO) in the southern URG, different hypothesis are tested: scattering of the seismic wavefield due to small-scale lateral heterogeneities, a vertical a -axis due to a vertical mantle flow related to the Kaiserstuhl Volcanic Complex, as well as a different preferred orientation of the olivine crystals (not A-type, but C-type) due to specific ambient conditions (high temperature, water content). [ABSTRACT FROM AUTHOR]

SUMMARY: For seismographic stations with short acquisition duration, the signal-to-noise ratios (SNRs) of ambient noise cross-correlation functions (CCFs) are typically low, preventing us from accurately measuring surface wave dispersion curves or waveform characteristics. In addition, with noisy CCFs, it is difficult to extract relatively weak signals such as body waves. In this study, we propose to use local attributes to improve the SNRs of ambient noise CCFs, which allows us to enhance the quality of CCFs for stations with limited acquisition duration. Two local attributes: local cross-correlation and local similarity, are used in this study. The local cross-correlation allows us to extend the dimensionality of daily CCFs with computational costs similar to global cross-correlation. Taking advantage of this extended dimensionality, the local similarity is then used to measure non-stationary similarity between the extended daily CCFs with a reference trace, which enables us to design better stacking weights to enhance coherent features and attenuate incoherent background noises. Ambient noise recorded by several broad-band stations from the USArray in North Texas and Oklahoma, the Superior Province Rifting EarthScope Experiment in Minnesota and Wisconsin and a high-frequency nodal array deployed in the northern Los Angeles basin are used to demonstrate the performance of the proposed approach for improving the SNR of CCFs. [ABSTRACT FROM AUTHOR]

Based on the solution of mechanisms in this study, Golbaf, Kuhbanan and Rafsanjan faults have a dominant right-lateral mechanism with a reverse component and Sarvestan fault has a pure reverse dominant mechanism. Earthquakes are mostly scattered around the city of Shiraz near the Sabzpooshan fault system and Borazjan fault. Solved mechanisms also show that earthquakes with a dominant right-lateral mechanism are related to the Karebas fault. Some earthquakes, which are related to the Sabzevaran fault are with the dominant mechanism of strike slip. Earthquakes of the Sabzpoushan fault are with the dominant mechanism of strike-slip right-lateral (N-S active plain). Mechanism of some earthquake is not compatible with any known faults in the range. In the interpretation of earthquakes in of all maps, the location error of the seismicity must also be considered. This error can reach up to ten kilometers (in some cases) due to the intermediate distance between the stations of the seismological networks. The mechanism of some of these faults, which were studied in previous works (geologically or seismologically), are consistent with the mechanism solved in this study. [ABSTRACT FROM AUTHOR]

Over the past two decades, the Al-Refaei district, a substantial town located in the Thi-Qar governorate in southern Iraq, has been subjected to numerous small to moderate-size earthquakes. A network of seven short-period seismic stations was installed in the Al-Refaei district to monitor seismic activity, a project that was initiated in 2014 and continued until 2018. The short-period seismic stations supplement the broadband seismic stations of the Mesopotamian Seismological Network (MPSN), which also serves this area. During the monitoring period, more than 56 earthquakes were recorded, of which 31 were detected by the short-period seismic stations and not reported by any other local or international seismic observatories. Data from the short-period and broadband seismic stations were analyzed using Geiger's least-squares method to determine accurate locations. The relocated earthquakes delineate a possible fault source with a northwest-southeast trend. The possible fault is not related to any known or previously studied fault. 3D seismic data of the area were evaluated and further supported the interpretation of a northwest-southeast trending fault, named the Al-Refaei fault. Integration of the seismological and 3D seismic data suggests that the Al-Refaei fault is a reverse fault with a S62˚E strike direction and a 43˚ dip angle. The strike and dip of the Al-Refaei fault were calculated from the analysis of the 3D seismic data. The reverse style of faulting was derived from the composite first motion method using the seismic station records of the short-period network. [ABSTRACT FROM AUTHOR]

Copyright of Journal of University of Anbar for Pure Science is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Dokuz Eylul University Muhendislik Faculty of Engineering Journal of Science & Engineering / Dokuz Eylül Üniversitesi Mühendislik Fakültesi Fen ve Mühendislik Dergisi is the property of Dokuz Eylul Universitesi Muhendislik Fakultesi Fen ve Muhendislik Dergisi and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A devastating earthquake took place on 8 April 1893, close to the town of Svilajnac, central Serbia. Over the past decade, significant historical data on the effects of this earthquake has been collected from a variety of sources, including books, scientific publications, reports, newspapers, and coeval chronicles. Additionally, this earthquake was recorded 750 km from the epicenter at the seismological station Rocca di Papa in Rome, Italy. Based on critical review and analysis of the historical data, we demonstrate that the epicentral area of this earthquake was 531 km2, and the macroseismic effects were recorded at epicentral distances up to 600 km towards the west (Vienna, Austria) towards the north, up to 500 km (Košice–Michalovce, Slovakia), towards the east up to 460 km (Brašov–Borsec, Romania); and towards the south up to about 300 km (Radoviš, North Macedonia). Finally, we show that the key parameters of the 1893 Svilajnac earthquake are as follows: (1) epicentral intensity, I0 = IX EMS-98, (2) the estimations of the moment magnitude and focal depth based on the observed intensities, MW = 6.8 and h = 13 km, respectively, and (3) the epicenter coordinates, 44.160° N and 21.354° E. [ABSTRACT FROM AUTHOR]

The article discusses the synthesis of seismograms for a multi-scale transversely isotropic (TI) saturated layered half-space subjected to seismic dislocation sources. The authors propose a revised stiffness matrix method to overcome the challenges of simulating wave propagation in multi-scale half-spaces with varying layer thickness and velocity. The method involves transforming the governing equations of motion, imposing the seismic source as body forces, and obtaining a global stiffness matrix by assembling each layer's exact stiffness matrix. The accuracy of the method is verified through comparisons with published literature, and the effects of superficial layers on ground motion are illustrated through numerical examples. The proposed method provides a fast and accurate way to synthesize seismograms in complex geological structures. [Extracted from the article]

We used local P and S waves, and regional Lg waves to investigate the Mw 4.9 Offshore Jeju Island earthquake, whose records show evidence of a complex rupture. This earthquake provides a rare window to understand the seismogenesis of moderate‐sized earthquakes on the southern Korea–East China Sea continental shelf. We computed the relative source time functions (RSTFs) by aligning the signals on the origin time of the main and its empirical Green's function (EGF) events, allowing us to use them as differential times of the EGF pair. We determined subevent locations using direct‐wave RSTFs, and captured the rupture variability of the two large subevents using waveform inversion of stacked Lg‐wave RSTFs. The first subevent rupture started by two weak nucleation phases and propagated slowly and bilaterally. Then the second subevent ruptured westward. Our analysis demonstrates that the Lg‐wave train observed at regional distances is useful in investigating detailed slip history. Plain Language Summary: In‐depth studies of small‐to‐moderate‐sized earthquakes in offshore regions are often limited by sparse seismographic station coverage and a lack of close observations. Here, we demonstrate the effective use of local P and S waves and regional Lg waves to investigate the detailed rupture process of the 2021 Mw 4.9 Offshore Jeju Island, Korea earthquake. Lg wave is a guided S wave composed of a superposition of post‐critical reflections in the crust. Detailed seismological analyses using Lg waves revealed that earthquake rupture processes can be spatially complex even in areas with low seismic activity. Our analysis demonstrates that the Lg wave observed at distances greater than 150 km from the epicenter alleviates the limited local station coverage and can be a very useful signal to image the detailed slip history of the earthquake. Our analysis revealed the rupture complexity of the earthquake, expressed as a cascade of four sequential ruptures consisting of two small nucleation phases and two large subevents. Such detailed knowledge of earthquake rupture evolution is critical for understanding seismogenesis in this stable continental region setting. Key Points: We demonstrate an approach to capture the complex rupture process of an offshore moderate‐sized earthquake using limited observationsDirect P and S waves and Lg waves are used to image a spatiotemporal slip history of the Mw 4.9 Offshore Jeju Island, Korea earthquakeResults show a cascading rupture of four subevents on a fault, offering a deeper understanding of event mechanism in low‐seismicity regions [ABSTRACT FROM AUTHOR]

The central part of the Pannonian Basin is characterised by low to medium seismicity. North central Hungary is one of the most dangerous areas of the country in terms of earthquakes, which also includes the area of the Mór Graben where some of the largest earthquakes occurred in Hungary's history. Recent activity has been observed in the Mór Graben. It has been established that earthquake swarms occur quite frequently in the graben. To further study these events, we deployed a temporary seismic network that operated for 20 months. Using the temporary network stations as well as permanent stations from the Kövesligethy Radó Seismological Observatory and the GeoRisk Ltd. networks we registered 102 events of small magnitudes. In this paper, we demonstrate and compare three different event detection methods based on the registered waveforms by the permanent and temporary stations to find the optimal one to collect a complete swarm list in the Mór Graben. After the hierarchical cluster analysis, we relocated the hypocentres using a multiple-event algorithm. Our results demonstrate that the most successful detector in this case is the "Subspace detector." We managed to create a complete list of the events. Our results indicate that the Mór Graben is still seismically active. [ABSTRACT FROM AUTHOR]

Hospitals are a fundamental component of a country's health system and are considered essential facilities for dealing with the consequences of natural disasters. Nevertheless, hospitals may be highly vulnerable structures. Despite the importance of these facilities, many hospitals have resulted severely damaged, and some of them have lost functionality even when subject to moderate earthquakes. In order to better understand the impact and influence of the seismic performance of non-structural components and systems on health facilities loss of function, this paper presents a comprehensive analysis of the loss of function degree observed in 17 hospitals affected by earthquakes with moment magnitudes (Mw) ranging between 5.1 and 8.8, located in countries such as the United States, Taiwan, Türkiye, Chile, Italy, El Salvador, Peru, Spain, Ecuador, and Mexico. The observed losses of function are correlated with structural and non-structural damages and the seismic demands imposed by the earthquakes, estimated from the accelerograms recorded at the closest seismological stations. As a result, the seismic demands triggering the non-structural damage states, and consequently the degree of function loss of the health infrastructure, are presented. Loss of function is classified as low or null, temporary, and permanent. It is observed that the seismic demands that limit the operation during earthquakes correspond to average roof drifts in the order of 1.0‰ and average peak floor accelerations in the range 0.16–0.23 g, highlighting the need for using seismic isolation technologies and implementing strict nonstructural design measures. [ABSTRACT FROM AUTHOR]

In the frame of the DAMAST (Dams and Seismicity) project, we deployed a dense high-fidelity seismological real-time network to investigate in detail the spatio-temporal seismicity distribution around the Enguri high dam, situated in the greater Caucasus in western Georgia. We aim at recording the weak seismicity in a 10 km distance around the dam structure. To lower the detection threshold by reducing the ambient background noise, we installed four seismic stations in shallow (ca. 20 m) and deep boreholes. From these stations, KIT1 with a depth of ca. 250 m is the deepest seismological station in Georgia. In this paper, we characterize the seismicity recorded by the local seismic network from October 2020 to July 2022. To have a better historical picture of the seismic activity, especially since the dam construction and initial operations, re-processing of the old seismological catalogs was carried out. This required digitizing the paper-only catalog copies prior to relocation. We finally obtain a uniform catalog for the Enguri region to characterize the seismicity and start investigating its possible relationship with the exploitation of the dam reservoirs. [ABSTRACT FROM AUTHOR]

Crustal configuration beneath the indenting northeast corner of the Indian Plate in the Eastern Himalayan Syntaxis has been investigated with the help of receiver function (RF) analysis of teleseismic earthquakes recorded by 19 broad-band seismological stations. The common conversion point stacking of RFs and 1-D velocity models obtained through inversion provide new information on the intracrustal structure. The study reveals the signature of the Main Himalayan Thrust (MHT) beneath the Lohit Valley at ∼22–26 km depth. The MHT is not prominent in the Siang window plausibly due to large-scale crustal deformation related to the formation of the window and antiform folding. Unlike in the western and central Himalaya, the MHT does not play a major role in seismogenesis in the Lohit Valley and Siang Window, where seismicity is active up to the crustal depth of ∼40 km. The crustal thickness increases from ∼38 km at Pasighat in the south to ∼50 km at the northernmost station (Gelling) in the Siang window. In Lohit Valley, the crustal thickness increases from ∼40 km at Mahadevpur in the west to ∼54 km in the Tidding–Tuting suture zone, which again shallows to ∼51 km in the eastern Lohit Plutonic Complex (Walong station). The thinner crust beneath the Tidding–Tuting suture compared to the Indus Tsangpo Suture Zone of northwest Himalaya is caused due to the differences in convergence rate, higher exhumation rate and mechanisms to accommodate collision and rotational tectonics. [ABSTRACT FROM AUTHOR]

This study analyzes the relationships between the stress changes produced by the water load variations due to the filling operations at the Pirrís Reservoir, Costa Rica, and the stress changes generated by three relevant earthquakes after the first impoundment. The earthquakes differ in their magnitude, distance from reservoir and depth. Two of them correspond to a shallow crustal faulting, and the third earthquake corresponds to a subduction thrust-fault. The first filling operations began in March 2011 and the daily time history of water levels was available until December 2017. The seismicity has been recorded by a dense local network of seismological stations operating since January 2008. Effects of both types of sources (water loads and earthquakes) were combined to obtain the total Coulomb Failure Stress in the reservoir area, analyzing which of them was dominant in each case and time. We then analyzed the effects of the pore pressure diffusion due to the water loads on the nearby seismicity including two of the studied earthquakes. Results lead to different conclusions depending on the characteristics of each earthquake. An important result is observed after the occurrence of the subduction earthquake, where the coseismic effects become dominant along the entire study area, eclipsing the effect of water loading at all depths. This shows that in a regime stressed by a regional earthquake, albeit of its moderate magnitude, and regional distance, the effect of water loads is barely perceptible. In the absence of tectonic activity, however, the impact of water loading is notable. [ABSTRACT FROM AUTHOR]

The lithosphere‐asthenosphere boundary and mid‐lithospheric discontinuities are primary attributes of the upper mantle. The Pannonian region is an extensional sedimentary basin enclosed by collisional orogens. Here, we estimate the negative phase depth of S‐to‐P receiver functions to image the lithospheric thickness and other discontinuities with high resolution, based on the recent dense seismological broadband networks. The lithosphere‐asthenosphere boundary is relatively shallow (<90 km) in the Pannonian Basin system, and deeper (∼90–140 km) in the surrounding orogens, where average surface heat flow values are higher (120 mW/m2) and lower (50–70 mW/m2), respectively. The 1D and 2D common conversion point migration with 3D velocity model provide comparable but different resolution images beneath the wider region of the Pannonian Basin. We obtained deeper values in the Western (∼120 km) and Southern‐Carpathians orogens (∼135 km). Furthermore, we provide new information on the lithospheric thickness and its seismic properties in the eastern part of the study region (e.g., Apuseni Mountains (∼95 km), Eastern‐Carpathians (∼120 km), Moesian Platform (∼90 km) and Transylvanian Basin (∼85 km). The shallower negative phase depth can be interpreted as the lithosphere‐asthenosphere boundary beneath the Pannonian Basin system in agreement with its high heat flow values. In contrast, the deeper negative phase depth estimates in the colder surroundings can be interpreted as intra‐ or mid‐lithospheric discontinuities, when compared with local seismic tomography models. In this region, the correlation with heat flow implies that the observed negative phase depth is of thermo‐chemical or rheological nature. Plain Language Summary: We conducted a detailed analysis of seismic waves beneath the Eastern Alps, Carpathians, Dinarides, and the Pannonian Basin to understand the structure of the Earth's deep interior and outermost tectonic shell, that is, its lithosphere in these regions. The most recent geophysical data available for this region are more than 20 years old. The thickness of the lithosphere in this area was not well known, and there were many open questions that were connected to its thermal properties and dynamic evolution. To address this, we collected data from permanent and temporary seismic stations in the study area between January 2002 and February 2022. This extensive data set, comprising 389 broadband seismological stations, allowed us to provide new information on the lithospheric structure and the geological evolution of this region. Key Points: Detailed S‐to‐P receiver function analysis in the circum‐Pannonian region with unprecedented station density1D and 2D migration of the S‐to‐P receiver function based on first negative phaseGeological interpretation and comparison of the lithospheric discontinuities with migrated cross‐sections and maps [ABSTRACT FROM AUTHOR]

Fault plane solution is one of the most important tools to determine the orientation of the stress field. The focal mechanism of earthquakes can be applied to determine the direction of rupture propagation, the structure of the fault and the stress field of the region. Dorouneh fault is the largest fault in Iran after the main Zagros fault with about 800 km length. The purpose of this study is to investigate the seismicity, the stress fields and the focal mechanism of earthquakes that have occurred across the three main segments western, middle and eastern parts of the Dorouneh fault. Therefore, the calculation of the focal mechanism is performed using the P-wave first-motion polarity. Also the stress situation of the events and the recognition of fault planes are presented in this research. Along this fault, the blocks have moved in both left and right directions, but certainly one of its last movements has had a right lateral motion. In this study, the waveforms recorded at the seismic stations of the National Seismological Center of Tehran University (IRSC), the National Center of Broadband Seismic Network of Iran belong to the International Institute of Earthquake Engineering and Seismology (IIEES) and seismic stations of Seismological Research Center at the Ferdowsi University of Mashhad were used. At first, the waveforms of each seismic event were combined with each other, and then the relocation of the events were determined based on new data set of this study (Figure 2). A number of high quality earthquake with a magnitude of more than 3 and an average depth of 14 km have been selected (their list is presented in table1) to calculate the fault plane solution. In order to calculate the mechanism of the recent earthquakes in the Khorasan region, interesting results have been obtained based on several methods (Assar Enayati, 1400). One of the common methods for estimating the mechanism of earthquakes, especially earthquakes with small magnitudes and at close distances from the epicenter, is the polarization of the first arrival of the P wave. Due to the dependence of the amplitude and polarization of the P wave on the focal mechanism, by determining the polarization of the first arrival of the seismic phase, the earthquake focal mechanism can be calculated. The results of focal mechanism solutions for significant events around Dorouneh fault show mostly left lateral strike slip motion which is consistent with the tectonic setting of the region. The difference in the focal mechanism of the events in the eastern and western parts of the fault is justified by the northward movement of the Lut block. The integration of data shows high accuracy in calculating the focal mechanism and more certainty about the results. Therefore, in the direction of the Dorouneh fault, the movements are both left-handed and right-handed from the seismic situation. The change in thefocal mechanism obtained from the seismic results, considering the stress axes changes, can represent the second and third order stress fields that balance the stress in this area today. The second-order stress can be related to continental rifting, isostasy adaptation, topography and deglaciation, and the third-order stress field can be related to the local stress source on a scale smaller than 100 km, which is influenced by the structural geometry, and interference between fault systems, topography and local density difference (Sheikh-ul-Islami et al., 2021). [ABSTRACT FROM AUTHOR]

Seismic ambient noise (SAN) energy can potentially blur regional and teleseismic arrivals as well as various microearthquakes at specific frequencies. Therefore, quantification of the SAN energy level in a region is required to optimize seismic station distribution for seismological investigations. Moreover, evaluation of station performance and noise source is possible from observation of SAN energy levels. The SAN energy distribution from seismic stations in the Bengal Basin (BB), Bangladesh has not yet been estimated. At the same time, this tectonically active and complex region is less studied using seismic methods. This study aims to quantify SAN energy and characterize its diurnal variation along with evaluating station performance at 11 seismic stations, which were temporarily installed in the deeper portion of the BB. Herein, the daily SAN energy level was determined within the period range of 0.02-30 s by estimating the power spectral density (PSD) of seismic data for 7 continuous days. SAN energy and its variation over time were observed using the probability density functions (PDFs) of PSDs and spectrograms, respectively. The sources of SAN energies at different period bands were also investigated by comparing the PSDs with daily variations in human activities, nearby noise sources, local meteorological factors (i.e., air temperature and precipitation), and sea level height. The insights from this study could be useful for the future deployment of seismic networks as well as seismological studies in the BB. [ABSTRACT FROM AUTHOR]

Different approaches to map seismic rupture in space and time often lead to incoherent results for the same event. Building on earlier work by our team, we 'time-reverse' and 'backpropagate' seismic surface wave recordings to study the focusing of the time-reversed field at the seismic source. Currently used source-imaging methods relying on seismic recordings neglect the information carried by surface waves, and mostly focus on the P -wave arrival alone. Our new method combines seismic time reversal approach with a surface wave ray-tracing algorithm based on a generalized spherical-harmonic parametrization of surface wave phase velocity, accounting for azimuthal anisotropy. It is applied to surface wave signal filtered within narrow-frequency bands, so that the inherently 3-D problem of simulating surface wave propagation is separated into a suite of 2-D problems, each of relatively limited computational cost. We validate our method through a number of synthetic tests, then apply it to the great 2004 Sumatra–Andaman earthquake, characterized by the extremely large extent of the ruptured fault. Many studies have estimated its rupture characteristics from seismological data (e.g. Lomax, Ni et al. , Guilbert et al. , Ishii et al. , Krüger & Ohrnberger, Jaffe et al.) and geodetic data (e.g. Banerjee et al. , Catherine et al. , Vigny et al. , Hashimoto et al. , Bletery et al.). Applying our technique to recordings from only 89 stations of the Global Seismographic Network (GSN) and bandpass filtering the corresponding surface wave signal around 80-to-120, 50-to-110 and 40-to-90 s, we reproduce the findings of earlier studies, including in particular the northward direction of rupture propagation, its approximate spatial extent and duration, and the locations of the areas where most energy appears to be released. [ABSTRACT FROM AUTHOR]

Shear‐wave velocity (Vs) structures can reveal the shallow sediment thickness and deep tectonic features of buried faults and geological units. They are important for reducing seismic and geological disasters in urban areas. Based on ambient noise data from the Tongzhou dense array (919 seismographic stations), we obtain a fine shallow‐deep (0–5 km) 3D Vs model, by jointly inverting the phase‐velocity dispersions of Rayleigh waves, including short‐period (0.3–2 s) multimode dispersions using the frequency‐Bessel transform method and the long‐period (2–6 s) fundamental‐mode dispersions using the fast marching method. Our results show that the Vs inhomogeneities agree well with the distribution of geological units. We use the 1 km/s isodepth of Vs as the reference thickness of quaternary sediments. Fengbo sag (FBS) and Dachang sag (DCS), which mainly show low velocity and density, have thick sediment thicknesses (approximately 550–600 and 320–420 m, respectively). The NE high‐velocity belt in Daxing high (DXH) has a thinner sediment thickness (∼230 m). Thus, FBS and DCS have a greater risk of earthquake hazards owing to the strong amplification effects of ground motion. Additionally, Vs distribution in the FBS, DCS, DXH, and Yanshan Fold Belt are spatially related to the medium density and buried faults (Nanyuan‐Tongxian, Daxing, and Xiadian faults). We infer that the Vs structures are associated with the controlling effects of these large normal faults and inhomogeneous strata density. The discontinuity of the NE high‐velocity belt in DXH probably results from the intense tectonic activity of Nankou‐Sunhe fault. Plain Language Summary: Quaternary sediments are usually fertile, and many metropolitan cities with dense populations are built on sedimentary basins. However, some large faults covered by thick quaternary sediments may negatively influence urban safety. S‐wave velocity (Vs) can provide useful information to better understand the sediment thickness and tectonic features of buried faults and geological units. We obtained a fine 3D Vs structure using ambient noise from a dense array (919 seismic stations) in Tongzhou. Our results show that the Fengbo and Dachang sags, mainly characterized by low velocities, have relatively thick sediment thicknesses (approximately 550–600 and 320–420 m, respectively). The Yanshan Fold Belt varies from the high‐velocity feature at 0–0.6 km to the low‐velocity feature at 0.6–5 km. With high velocity, the west portion of Daxing has a thinner sediment thickness (∼230 m). Four normal buried faults and media density probably affected the distribution of the Vs distribution. Key Points: An improved Vs model in Tongzhou is obtained by jointly inverting the dispersions from frequency‐Bessel transform and fast marching methodsFour buried normal faults and medium density in the study area have probably affected the distribution of shear‐wave velocityThe thickness of quaternary sediments revealed by 1 km/s of shear‐wave velocity is closely related to the four normal faults [ABSTRACT FROM AUTHOR]

One important feature of the Greenland Ice Sheet (GrIS) change is its strong seasonal fluctuation. Taking advantage of deployed seismographic stations in Greenland, we apply cross‐component auto‐correlation of seismic ambient noise to measure in‐situ near surface relative velocity change (dv/v) in different regions of Greenland. Our results demonstrate that dv/v measurements for most stations have less than 3 months lag times in comparison to the surface mass change. These various lag times may provide us constraints for the thickness of the subglacial till layer over different regions in Greenland. Moreover, in southwest Greenland, we observe a change in the long‐term trend of dv/v for three stations, which might be consistent with the mass change rate (dM/dt) due to the "2012–2013 warm‐cold transition." These observations suggest that seismic noise auto‐correlation technique may be used to monitor both seasonal and long‐term changes of the GrIS. Plain Language Summary: The changes of the Greenland Ice Sheet (GrIS) have important implications for both scientific research and human society. Due to its large size, the change of the GrIS varies at different regions. Here, we apply a seismic monitoring technique to study the GrIS mass change by using seismographic stations deployed in Greenland. The advantage of using this technique is that we are able to monitor different locations in a relatively simple, low‐cost and in‐situ way, and obtain indicative information about the ice mass change over time. We specify the seasonal fluctuations of seismic signals and connect them with the subglacial setting at different regions in Greenland, and explore the potential of using these seismic techniques to monitor the long‐term changes of the GrIS. Key Points: The seasonal variations of relative velocity change (dv/v) have <3 months lag with respect to the surface Greenland Ice Sheet (GrIS) changeLarger lag times of dv/v may provide constrains for thicker subglacial till layers in the central Greenlanddv/v may be used for monitoring long‐term GrIS mass change [ABSTRACT FROM AUTHOR]

The Athenet network is the network of the Seismological Laboratory of the National and Kapodistrian University of Athens. We present the geophysical investigation that has been carried out at six seismological stations of the Athenet network for their site characterization. More specifically, at the location of each seismological station, four geophysical methods have been carried out: Seismic Refraction Tomography (SRT), Multichannel Analysis of Surface Waves (MASW), the Horizontal to Vertical Spectral Ratio (HVSR) technique, and Electrical Resistivity Tomography (ERT). The applied geophysical survey provided important information regarding the site characterization at the selected seismological stations, including key parameters such as the fundamental frequency fo, the shear-wave velocity VS, the average shear-wave velocity for the upper 30 m depth (VS30), the seismic bedrock depth, the soil type, and the subsurface geology. Moreover, selected elastic moduli (Poisson's ratio, shear, bulk, and Young moduli) have been calculated. The site characterization information contributes to the determination of the amplification factors for each site that can lead to more accurate calculation of Peak Ground Acceleration (PGA) or Peak Ground Velocity (PGV) and, therefore, trustworthy Probabilistic and Stochastic Seismic Hazard Assessments. The derived fundamental frequency for the seismological stations of VILL, LOUT, THAL, and EPID have been determined to be equal to 10.4, 2.7, 1.4, and 7.1 Hz and their amplification factors to be 1.9, 3.1, 1.7, and 2.6, respectively. For stations MDRA and ATAL, these parameters could not be determined. [ABSTRACT FROM AUTHOR]

The Western Ghats (WG) is one of the great escarpments that extend ~1500 km parallel to the west coast of India in the direction of NNW-SSE. We deployed a network of seven broadband seismological stations along the WG to decipher its evolution. In the present study, we investigate the characteristics of different kinds of noises at the stations by utilizing the power spectral density (PSD) measurements. Further, the results are compared with the global standard noise models to assess the data quality. The PSD results reveal that the short period (0.1–1 s) cultural noise is more prominent at stations AGMB, SDPR and MGLI when compared to the other stations, especially during day hours of Indian Standard Time (IST) zone since these sites were in the proximity of roads. The seasonal variations are observed especially in the microseismic period range and noise levels are more prominent in the months of July to August since the western part of India experiences peak monsoon during this period. These variations are observed especially at PCH and KNUR stations as their locations were near the coastline. Furthermore, the results indicate that the noise levels are more prominent in vertical components than that of horizontal components in the microseismic period range whereas it is reversed in the short and long period ranges. Later, the results indicate that the noise levels at all the localities of stations are within the global standard noise models, which suggests that our installation of broadband seismological stations has been successful at all seven locations and has good data quality. [ABSTRACT FROM AUTHOR]

The Earth's asthenosphere is a mechanically weak layer characterized by low seismic velocity and high attenuation. The nature of this layer has been strongly debated. In this study, we process 12 years of seismic data recorded at the global seismological network stations to investigate SS waves reflected at the upper and lower boundaries of this layer in global oceanic regions. We observe strong reflections from both the top and the bottom of the asthenosphere, dispersive across all major oceans. The average depths of the two discontinuities are 120 and 255 km, respectively. The SS waves reflected at the lithosphere and asthenosphere boundary are characterized by anomalously large amplitudes, which require a ∼12.5% reduction in seismic velocity across the interface. This large velocity drop can not be explained by a thermal cooling model but indicates 1.5%–2% localized melt in the oceanic asthenosphere. The depths of the two discontinuities show large variations, indicating that the asthenosphere is far from a homogeneous layer but likely associated with strong and heterogeneous small‐scale convection in the oceanic mantle. The average depths of the two boundaries are largely constant across different age bands. In contrast to the half‐space cooling model, this observation supports the existence of a constant‐thickness plate in oceanic regions with a complex and heterogeneous origin. Plain Language Summary: In the plate tectonic theory, the outermost shell of the Earth consists of a small number of rigid plates (lithosphere) moving horizontally on the mechanically weak asthenosphere. In oceanic regions, the lithosphere is thought to be formed by the gradual cooling of the hot mantle. Therefore, the thickness of the plate depends on the age of the seafloor. The problem with the classic half‐space cooling model is that bathymetry and heat flow measurements at old seafloors do not follow its predicted age dependence. A modified theory, called the plate model, can better explain those geophysical observations by assuming additional heat at the base of an oceanic plate with a constant thickness of about 125 km. However, such a constant‐thickness plate has not been observed in seismology. In this study, we image the asthenosphere boundaries using a global dataset of seismic waves reflected off the Earth's internal boundaries. We observe strong reflections from both the top and the bottom of the asthenosphere, across all major oceans. The amplitudes of these waves can be explained by 1.5%–2% of partial melt and the average boundary depths are independent of seafloor age. This observation supports the existence of a constant‐thickness plate in the global oceans with a complex origin. Key Points: SS precursors reveal depths of the lithosphere–asthenosphere boundary independent of seafloor ageThe oceanic lithosphere–asthenosphere boundary is a strong reflector and can be explained by 1.5%–2% of partial meltLarge depth variations of the top and the bottom boundaries of the asthenosphere suggest a heterogeneous melting process [ABSTRACT FROM AUTHOR]

The seismic-wave attenuation parameters (seismic quality factor at 1 Hz Q0 and frequency parameter n) in the lithosphere of the Amur River region were determined. We estimated the attenuation parameters on a regional scale using the coda of Lg surface waves, as well as their key and highest spatial variations. Q0 varies from 380 in the southern Primorye to 600 in the northwestern Amur River region. Based on the coda of volume S-waves from nearby earthquakes recorded at the local seismological stations of the Bureya Hydropower Plant, we obtained the average quality factor and frequency in the study area with a radius of a few hundred kilometers around a hydropower plant. For a window width of 20 s, Q0 = 103 and n = 0.806. These values are typical for moderate seismicity regions and confirm the high seismic potential of the study area. The actual attenuation parameters of seismic waves make it possible to relate the parameters of the sources of hypothetical earthquakes and the expected intensity of ground shaking caused by them more accurately and more reasonably, and thus to eliminate one of major simplifications of General Seismic Zoning maps. [ABSTRACT FROM AUTHOR]

Lombok is one of the islands in the transitional zone from the Sunda Arc to the Banda Arc, Indonesia. In the mid-2018, the island of Lombok was shaken by a series of strong earthquakes, started with a moment magnitude (Mw) 6.4 earthquake on July 29, 2018 followed by earthquakes on August 5 (Mw 7.0), August 9 (Mw 5.9), and August 19 (Mw 6.3 and 6.9). Some researchers suggested that this phenomenon occurred due to a segmentation rupture in the northern part of Lombok Island. This study aims to obtain information on the distribution of the Lombok earthquake fault zone 2018 and also to understand the character of seismic anisotropy around the Lombok earthquake fault zone 2018 through Shear Wave Splitting (SWS) study. Splitting, or S-wave separation, occurs when the S wave passes through an anisotropic medium. The S wave is split into fast and slow S waves with almost orthogonal polarizations and has parameters such as delay time and polarization direction of the fast S wave. To determine the SWS parameters, we used a Lombok earthquake aftershock data set recorded from 4 August to 9 September 2018, using 16 seismographic stations. The steps taken to obtain the SWS parameters are event selection, windowing using short time Fourier transform, and rotation-correlation process. The results of the SWS analysis indicate that the fast polarization directions probably have a linkage with the local fault system and the fault related to the Lombok earthquake fault zone. [ABSTRACT FROM AUTHOR]

Earthquake early warning (EEW) systems provide seconds to tens of seconds of warning time before potentially-damaging ground motions are felt. For optimal warning times, seismic sensors should be installed as close as possible to expected earthquake sources. However, while the most hazardous earthquakes on Earth occur underwater, most seismological stations are located on-land; precious seconds may go by before these earthquakes are detected. In this work, we harness available optical fiber infrastructure for EEW using the novel approach of distributed acoustic sensing (DAS). DAS strain measurements of earthquakes from different regions are converted to ground motions using a real-time slant-stack approach, magnitudes are estimated using a theoretical earthquake source model, and ground shaking intensities are predicted via ground motion prediction equations. The results demonstrate the potential of DAS-based EEW and the significant time-gains that can be achieved compared to the use of standard sensors, in particular for offshore earthquakes. [ABSTRACT FROM AUTHOR]

The Kolba permanent seismic station was installed in 2020 at the Kolba geophysical station (affiliated with the Northern Territorial Administration for Hydrometeorology and Environmental Monitoring), near the settlement of Dikson, Krasnoyarsk krai, in order to increase the sensitivity of the Arkhangelsk Seismic Network (affiliated with the N. Laverov Federal Center for Integrated Arctic Research, Ural Branch, Russian Academy of Sciences), which carries out seismic monitoring in the Barents–Kara region and adjacent areas. For regional earthquakes in the European sector of the Arctic, the representative magnitude was determined at MLrep = 3.4. The Kolba seismic station records local events of different nature with magnitudes from 0.8 to 1.7. The dependence of the number of revealed earthquakes on the level of microseismic noise is revealed. [ABSTRACT FROM AUTHOR]

To solve many geological and geophysical problems, in particular, prediction of strong earthquakes, seismic zoning, and earthquake-resistant construction, it is necessary to have reliable data on the distribution of earthquake hypocenters in the study area. In turn, the completeness of data on the distribution of earthquake hypocenters and accuracy of their determination largely depend on the efficiency of the observation system. We evaluate the efficiency of the actual network of seismological observations in Karelia, which consists of seven seismic stations. The efficiency of the seismological observation network is estimated by the minimum magnitudes of seismic events recorded in the considered region and the minimum errors in determining the main parameters (origin time and hypocentral coordinates) of the recorded events. Calculation of the minimum earthquake magnitudes for the Karelian seismological network shows that a station amplification of 30 000, the network is able to record earthquakes with a magnitude slightly less than 2, with a tendency towards a decrease in this minimum magnitude, provided that the event is recorded by at least three stations. The errors in determining earthquake epicentral coordinates in latitude δφ (km) and longitude δλ (km) do not exceed 1–2 km in the center of the network, and 6 and 11 km on the periphery, respectively. The system's errors in determining the depths of earthquake sources H (km) do not exceed 5 km in the vicinity of the stations and 25 km throughout the territory of Karelia. [ABSTRACT FROM AUTHOR]

As part of the FloodRisk project, the influence of rising mine water in abandoned coal mines on induced seismicity is investigated. The Seismological Observatory of the Ruhr University Bochum operates a monitoring network for the whole Ruhr area (North Rhine-Westphalia, Germany) since 1983. The local scale FloodRisk network was installed in the eastern part of the Ruhr area in 2020. The continuous monitoring opens up the opportunity for a long-term study of seismicity in combination with water levels related to mining in the region. The resulting database for the eastern Ruhr area includes over 13,000 induced earthquakes in a period of 26 years during active mining, very few events in the postmining phase before the onset of flooding and more than 1,700 events in the first two and a half years of flooding. The seismological database is supplemented by the mine water levels, which are regularly measured at various measuring points distributed over the study dewatering area “Haus Aden” and made available by Ruhrkohle Aktiengesellschaft (RAG). Seismic activity was highest in the phase of active mining and concentrated in the vicinity of the mining areas. After the end of mining, only very low seismicity was detected. With the start of flooding, significantly more events were registered again. The rise curve of the mine water level and the temporal and spatial distribution of the seismicity are observed and analysed. Five temporal flooding phases are identified in which the correlated seismicity shows different distribution patterns. Phases in which the levels of individual sections of the mine merge in flooding show particularly high seismicity. A strong spatial clustering of well-localised events occurs below the deepest flooded levels of the mine. Several mechanisms that alter the stress in active mining and flooded mines and induce seismic events are known from previous studies. To apply this to our study, particular attention is given to the spatial distribution of seismicity in relation to known geologic and mining structures. In the flooding phase, most of the seismicity is localised in the area below the flooded drifts. [ABSTRACT FROM AUTHOR]

The northwestern corner of South America presents a highly complex geodynamical setting including the convergence between South America, Nazca, and Caribbean plates; which also entails heterogeneity and complexity in the lithospheric structure. Here, we present depth‐migrated common‐conversion point (CCP) teleseismic receiver function profiles carried out using seismological data between 2011 and 2020 from the Colombian Geological Service, combined with some stations of observatories and international networks. These profiles provide better constraints on the lateral interpretation of the main lithospheric discontinuities in this region. We provide an updated crustal thickness map displaying some differences from previous studies, especially in the northernmost part of the cordilleran system. Our results also show some intracrustal features such as the regional detachment surface beneath the Eastern Cordillera and the presence of deep melt reservoirs under the Central Cordillera and the Paipa‐Iza complex in the Eastern Cordillera. We also discuss the lithospheric thickness and the potential existence of a highly hydrated and serpentinized mantle wedge under the forearc over the slab segment south of the Caldas tear. Furthermore, the CCP profiles further support the subduction system segmentation under northwestern South America, with at least five slab segments, two of them overlapping between ∼5.5 and ∼8°N, three belonging to the Nazca plate, and two having a Caribbean origin. The Bucaramanga nest appears to be linked to the interaction between the two northmost slab segments, while the Cauca cluster might be related to a slab dehydration process of a highly fractured zone. Plain Language Summary: The Colombian tectonic configuration is highly complex with the convergence of three major tectonic plates. Despite extensive recent studies in this region, some of the important tectonic features are still under discussion. In this study, we present cross‐section images of the lithospheric and upper mantle structure beneath Colombia, carrying out an analysis of teleseismic wave conversions corresponding to data collected between 2011 and 2020 by the Colombian Geological Service, volcanological and seismological observatories, and international stations. The results show that the crust is thinner than estimated in previous studies in the northernmost part of the Colombian cordillera system, and provide some material on intracrustal features and lithospheric thickness. Moreover, our images support other studies on the subduction system in this area, showing the presence of five slab segments on the Pacific side subducting beneath Colombia, including an overlapping segment between ∼5.5 and ∼8°N. The two densest seismic clusters, the Bucaramanga nest and the Cauca cluster, seem to be linked to the interaction of two plates at depth and the dehydration of a fractured slab zone, respectively. Key Points: Crustal thickness beneath northwestern South America with some significant changes from previous studiesWe observe five different slab segments under northwestern South AmericaRegional detachment surface under the Eastern Cordillera ranging between 10 and 30 km depth [ABSTRACT FROM AUTHOR]

Crustal configuration beneath the northeastern region of India has been investigated with the help of receiver function (RF) analysis of teleseismic earthquakes recorded by 19 broadband seismological stations. We adopted the H‐k stacking method to estimate crustal thickness and Poisson's ratio beneath each recording station. The study reveals a large variation in crustal thickness and Poisson's ratio which are correlated with the complex geology and tectonics of the region. The crust is observed to be thinner (36.5–41.6 km) beneath Bengal Basin, Shillong Plateau, and the Brahmaputra valley compared to the Indo‐Burma Ranges (IBR) (~40–54 km) and Arunachal Higher Himalaya (TAWA station, ~45 km) and Sikkim Himalaya (GTK station, ~46.5 km). A large variation of Poisson's ratio is observed in the region (~0.230–0.306). Poisson's ratio is generally low‐to‐intermediate in the Shillong‐Mikir Plateau, Bengal Basin, and the Brahmaputra Valley, while it is intermediate‐to‐high in the Tripura Fold Belt and the northern part of the IBR. The high Poisson's ratio in the Tripura Fold Belt is due to the presence of basaltic basement rock and clay minerals existing in the sedimentary rocks, whereas the presence of partially serpentinized rock in the ophiolitic mélange complex causes a high Poisson's ratio in the IBR. [ABSTRACT FROM AUTHOR]

The splitting of SK(K)S phases is an important observational constraint to study past and present geodynamic processes in the Earth based on seismic anisotropy. The uniqueness of the derived models is unclear in most cases, because the azimuthal data coverage is often limited due to recordings from only a few backazimuthal directions. Here, we analyze an exceptional dataset from the permanent broadband seismological recording station Black Forest Observatory (BFO) in SW Germany with a very good backazimuthal coverage. This dataset well represents the potential teleseismic ray paths, which can be observed at Central European stations. Our results indicate that averaging splitting parameters over a wide or the whole backazimuthal range can blur both vertical and lateral variations of anisotropy. Within the narrow backazimuthal interval of 30–100°, we observe a complete flip of the fast polarization direction. Such a splitting pattern can be caused by two layers with about NW–SE (lower layer) and NE-SW (upper layer) fast polarization directions for shear wave propagation. However, the possible model parameters have quite a large scatter and represent only the structure to the northeast of BFO. In contrast, within the wide backazimuthal range 155–335°, we prevailingly determine null splits, hence, no signs for anisotropy. This null anomaly cannot be explained satisfactorily yet and is partly different to published regional anisotropy models. Our findings demonstrate that there is significant small-scale lateral variation of upper mantle anisotropy below SW Germany. Furthermore, even low-noise long-term recording over 25 years cannot properly resolve these anisotropic structural variations. [ABSTRACT FROM AUTHOR]

The article presents the following: the results of deformation monitoring by GNSS tools at the FSUE Radon radioactive waste disposal site (Moscow oblast); a brief history of the development of the geodynamic observation network at the industrial site of Radon. the results and geodynamic interpretation of GNSS observations of Earth surface movements for 2008–2017. the results of studies on upgrading Radon's geodynamic structure, taking into account the creation of a single digital space for the industrial site to manage its lifecycle. The article summarizes the experience in creating life cycle monitoring systems at radioactive waste disposal sites using modern digital measurement methods. [ABSTRACT FROM AUTHOR]

An improved statistical method for determining the resonance frequencies of soils from spectral H/V ratios is presented. The combination of developed methodological and computational techniques makes it possible to identify with high reliability the resonance frequencies of the soil sequence and fundamental frequencies of the natural vibrations of structures and their elements based on engineering seismological observations. The authors demonstrate the possibility of refining the seismic soil model of a site and compiling spatial models of the change in depths of seismic boundaries of layers of the soil sequence from the results of frequency analysis of records of microseisms and seismic events. The use of the described engineering and seismological observations and methodological techniques makes it possible to instrumentally estimate the increase in amplitudes of vibrations of structures and their individual elements at resonance frequencies and obtain a sufficiently detailed seismometric floor-by-floor description of the vibrational characteristics of buildings and structures. [ABSTRACT FROM AUTHOR]

The authors have studied the characteristics of the short-period S-wave attenuation field in the lithosphere of southwest Alaska (in the Alaska subduction zone). Records of seismic station KDAK, obtained for shallow earthquakes within the distance range of ~250–750 km, were processed. We used a method that analyzes the ratio of maximum amplitudes in Sn and Pn waves (parameter Sn/Pn). The correlation dependence of this parameter on distance for wave lines crossing rupture zones of three large and great earthquakes is plotted: the Great Alaskan earthquake of March 28, 1964 (MW = 9.2), the Simeonov earthquake of July 22, 2020 (MW = 7.8), and Chignik earthquake of July 29, 2021 (MW = 8.2). It was established that this dependence goes a little higher than similar dependences obtained earlier for regions of southwest Japan and central Chile, and much higher than for the region of northeast Japan. The reasons for the substantial differences of these dependences in different regions are discussed. The authors consider heterogeneities of the attenuation field in the rupture zones of the Simeonov earthquake and its largest aftershock (MW = 7.6), as well as of the Chignik earthquake. [ABSTRACT FROM AUTHOR]

The modern seismological network of Karelia consists of four seismic stations. The number of network stations is small, and they are unevenly distributed over the territory of Karelia. Therefore, this seismological network is not efficient enough, and seismic events (earthquakes and quarry blasts) with different minimum magnitudes and different accuracies are recorded at different points in the territory. In order for events occurring at different points of Karelia to be recorded with the same accuracy and the same minimum magnitude, it is necessary to arrange the system's seismic stations more evenly throughout the territory; i.e., the observing system must have the optimal configuration. Calculation of the minimum magnitudes of recorded seismic events for the optimal seismological network from 65 new and 4 currently functioning seismic stations shows that with an amplification in recording channels of 50 000, the network will reliably record earthquakes with a magnitude of 1.0 or more throughout Karelia. At the same time, the position of the seismic stations of such a network in Karelia is determined up to a parallel shift and arbitrary rotation of the entire observation system. Errors in determining the epicentral coordinates in latitude and longitude within the network will not exceed 0.5 km. The errors in determining the depths of earthquake sources recorded by the system throughout Karelia do not exceed 1.0 km at the center of the network and can reach 2.0 km only on its periphery. [ABSTRACT FROM AUTHOR]

A steadily increasing number of citizen seismological stations, often located in populated areas, record a plethora of man-made events. These events are especially of interest, when they are caused by criminal activity or man-made explosions. On 4 December 2021, during an attempted robbery of an automated teller machine (ATM) in Bonn-Röttgen, Germany, the burglars used explosions. The seismic effects of the explosions were recorded with a Raspberry Shake (RS) station at a distance of 580 m from the site. While working on the analysis of this signal, another attack on an ATM on 23 February 2022 in Kürten-Dürscheid was recorded by another RS station, this time at 830-m distance with an instrument that also included an air pressure channel. The seismic signatures of both events indicate similar procedures in both cases whereby a larger explosion was quickly followed a smaller explosion after 21 s and 49 s, respectively. An estimate of the charge weight of the explosions shows that ratios of the strength of the first to second explosion were 21:1 and 9.4:1 in the Röttgen and Dürscheid attacks, respectively. [ABSTRACT FROM AUTHOR]

Seismologists found a significant deterioration in station quality after installation of wind turbines (WTs), which led to conflicts between WT operators and seismic services. We compare different techniques to reduce the disturbing signals from WTs at seismological stations by selection of an affected station. WT noise and earthquake signals have overlapping frequency bands, and thus spectral filtering cannot be used. As a first method, we apply the continuous wavelet transform on our data to obtain a time-scale representation. From this representation, we estimate a noise threshold function either from noise before the theoretical P-arrival or using a noise signal from the past with similar ground velocity conditions at the surrounding WTs. As a second method, we use a denoising autoencoder (DAE) that learns mapping functions to distinguish between noise and signal. In our tests, the threshold function performs well when the event is visible in the raw or spectral filtered data, but it fails when WT noise dominates. The use of the threshold function and pre-noise can be applied immediately to real-time data and has low computational cost. Using a noise model from our prerecorded database at the seismological station does not improve the result and is more time consuming. In contrast, the DAE is able to remove WT noise even when the event is completely covered by noise. However, the DAE must be trained with typical noise samples and high signal-to-noise ratio events to distinguish between signal and interfering noise. [ABSTRACT FROM AUTHOR]

The West and Central African Rift System (WCARS) is the only stable continental geological structure on Earth that is formed by large‐scale topographic massifs (swells). However, knowledge of the origin and evolution of the WCARS remains limited mainly due to the scarcity of high-resolution geophysical observations. To better understand the crustal structure beneath the entire WCARS, we use the XGM2016 global gravitational model and the ETOPO1 global topographic-bathymetric model to determine a gravimetric Moho (crust-mantle boundary) model constrained by seismic Moho depth estimates at 41 seismological stations distributed irregularly within the study area. The result reveals a regional Moho deepening to ∼40 km beneath the Hoggar, Aïr and Tibesti Massifs. The largest Moho deepening to ∼46 km is detected beneath the Archean Congo Craton, while the Moho depth under the Adamawa Plateau reaches 42 km. The Moho geometry beneath the Chad Basin, the Chad Lineament and the Termit Basin is relatively even with the Moho depth mostly within 24–26 km. A significant Moho deepening as well as large Moho depth variations within 32–45 km beneath the Saharan Metacraton and the Congo Craton (especially under its northern margin) reflect the metacratonization processes that occurred during the Neoproterozoic. The Niger Delta and the Benue Trough are characterized by a very thin continental crust with the Moho depth varying from ∼20 km in the south along the Atlantic coastline to ∼24 km in the northeastern branch of the Cretaceous Benue Trough around the Garoua-Yola Rift. [ABSTRACT FROM AUTHOR]

On 3 March 2021 (10:16, UTC), a strong earthquake, Mw 6.3, occurred in Elassona, Central Greece. The epicenter was reported 10 km west of Tyrnavos. Another major earthquake followed this event on the same day at Mw 5.8 (3 March 2021, 11:45, UTC). The next day, 4 March 2021 (18:38, UTC), there was a second event with a similar magnitude as the first, Mw 6.2. Both events were 8.5 km apart. The following analysis shows that the previous events and the most significant aftershocks were superficial. However, historical and modern seismicity has been sparse in this area. Spatially, the region represents a transitional zone between different tectonic domains; the right-lateral slip along the western end of the North Anatolian Fault Zone (NAFZ) in the north Aegean Sea plate-boundary structure ends, and crustal extension prevails in mainland Greece. These earthquakes were followed by rich seismic activity recorded by peripheral seismographs and accelerometers. The installation of a dense, portable network from the Aristotle University of Thessaloniki team also helped this effort, installed three days after the seismic excitation, as seismological stations did not azimuthally enclose the area. In the present work, a detailed analysis was performed using seismological data. A seismological catalogue of 3.787 events was used, which was processed with modern methods to calculate 34 focal mechanisms (Mw > 4.0) and to recalculate the parameters of the largest earthquakes that occurred in the first two days. [ABSTRACT FROM AUTHOR]

Passive seismic measurements allow the study of the deeper Earth beneath the thick Antarctic ice sheet cover. Due to logistical and weather constraints, only a fraction of the area of the Antarctic ice sheet can be surveyed with long-term or temporary sensors. A fundamental limitation is the power supply and operation of the instruments during the polar winter. In addition, there is only a limited time window during the field seasons to deploy the stations over the year. Here we present a rapidly and simple deployable self-sufficient mobile seismic station concept. The station consists of different energy supply modules aligned according to the survey needs, measuring duration, and survey aim. Parts of the concept are integrated into an already existing pool of mobile stations and in the seismological network of the geophysical observatory at Neumayer III Station. Other concepts and features are still under development. The overall goal is to use these temporary mobile arrays in regions where little is known about local and regional tectonic earthquake activity. [ABSTRACT FROM AUTHOR]

We present a new high‐resolution image of the crust beneath the western Himalaya‐Asia convergence zone encompassing the geographical domain of western Himalaya‐western Tibet‐Ladakh‐Karakoram‐Pamir‐Hindu Kush, using ambient noise cross‐correlations from 530 seismological stations along with surface wave observations from 1,261 earthquakes recorded over the network. The 3‐D shear wave velocity image is created using 22,726 inter‐station Rayleigh wave dispersion measurements from 5 to 60 s period at a horizontal resolution of less than 0.5° × 0.5° following the Bayesian Trans‐dimensional Tree tomography approach. The Moho beneath the Himalayas and south Tibet correlates with a velocity transition of 4.4–4.6 km/s and a reduced velocity transition of 4.0–4.2 km/s in northern Tibet and the Pamir. We used the Moho depth and the nature of high‐velocity lower crust (Vs > 4.0 km/s) to map the northern limit of the Indian crust that extends beyond the Qiangtang block in western Tibet (77–82°E) from its previously assumed boundary in the Lhasa block and till the central Pamir farther west. The velocity image reveals discontinuous low‐velocity zones (LVZs; Vs < 3.4 km/s) in the mid‐crust of western Tibet and the Pamir that do not support the existence of the channel flow model. The LVZs in the Pamir correlate with the surface distribution of gneiss domes. The lowest velocities (Vs < 3.2 km/s) are observed over the Ladakh‐Karakoram batholith and the Nanga Parbat region. The study suggests a continuation of LVZs across the Karakoram Fault at a depth below 20 km, indicating the fault's upper crustal depth extent. Plain Language Summary: The Tibetan plateau, the Himalayas, and the Pamir are the most spectacular products of the continued collision of the Indian plate with the Asian plate since about 60 Ma. To provide constraints on the geodynamic processes responsible for the creation of these features, we present a high‐resolution 3‐D shear velocity model of the underlying crust beneath the poorly studied western segment of the India‐Asia collision zone. Using crustal thickness and the nature of the high‐velocity lower crust, we map the underthrusted Indian crust extending close to the northern end of western Tibet, and till the central Pamir farther west. As a consequence of the underthrusting, the low viscosity Indian crust beneath Tibet was proposed to flow southward and extrude along the Himalayan front. We examine the validity of this "channel flow model". Our velocity model shows discontinuous low‐velocity zones (LVZs) in the middle crust of western Tibet and the Pamir that do not support the presence of a pervasive channel flow, questioning the validity of the "channel flow model". In the Pamir, the LVZs correlate with gneissic domes. Our model also shows that the Karakoram Fault is a shallow crustal feature as it does not disrupt the mid‐crustal LVZs. Key Points: The northern limit of the Indian crust extends beyond the Qiangtang block in western Tibet and till the central Pamir farther in the westLaterally discontinuous mid‐crustal low‐velocity zones do not support the pervasive channel flow modelThe Karakoram Fault is an upper crustal feature extending to a depth of 20 km [ABSTRACT FROM AUTHOR]

In order to examine the shallow geology under the site of the Skopje Seismological Observatory (SKO), Naka- mura technique was used on a set of selected seismic records from its strong motion instruments. The assessment of site conditions and amplification behavior was performed under different input levels of seismic ground motions. The datasets for analysis consisted of three types of seismic registrations: the first type were the microtremor measure- ments, the second type was a nearby man-made explosion, and the third type was a moderate size local earthquake with a magnitude of ML5.3 which occurred on 11th of September 2016. Horizontal vs. vertical ratio of the components recorded for all three types of source vibration were calculated. Similar predominant peaks and frequency distribution were observed when records from the local earthquake, the explosion and the ambient noise were analyzed. The results of the analysis with Nakamura method were compared with interpretations from the geological and geotechnical maps at the station location. Our findings support the idea that such geophysical methods can detect the underlying structural profile to a first approximation and can be used to develop consistent velocity models for large areas without expensive drilling deployments. [ABSTRACT FROM AUTHOR]

Seismographs record earthquakes and also record various types of noise, including anthropogenic noise. In the present study, we analyse the influence of the lockdown due to COVID-19 on the ground motion at CSIR-NGRI HYB Seismological Observatory, Hyderabad. We analyse the noise recorded a week before and after the implementation of lockdown by estimating the probability density function of seismic power spectral density and by constructing the daily spectrograms. We find that at low frequency (<1 Hz), where the noise is typically dominated by naturally occurring microseismic noise, a reduction of ~2 dB for secondary microseisms (7–3 s) and at higher frequency (1–10 Hz) a reduction of ~6 dB was observed during the lockdown period. The reduction in higher frequencies corresponding to anthropogenic noise sources led to improving the SNR (signal-to-noise ratio) by a factor of 2 which is the frequency bandwidth of the microearthquakes leading to the identification of microearthquakes with Ml around 3 from epicentral distances of 180 km. [ABSTRACT FROM AUTHOR]

[Display omitted] • The crustal thickness varies from ∼35 km in the Brahmaputra Valley to ∼46 km in IBR. • Shear wave velocity in the mantle (4.1–4.3 km/s) is lower than the global average. • Detected Hales discontinuity at a depth range of ∼54–78 km in the northeast India. The crust and shallow upper mantle structure beneath the Upper Brahmaputra Valley, Indo-Burma Ranges, and Bengal Basin of Northeast India have been investigated based on receiver function (RF) analysis of teleseismic earthquakes recorded by 11 seismological stations. The study reveals a thin crust (∼35 km) beneath the Brahmaputra Valley (at JORH station) with a surface sedimentary layer of ∼4 km thick. The crustal thickness is observed to increase towards the north in the Himalaya (∼40 km at ZIRO and ITAN) and to the south (up to ∼46 km at KOHI). The crustal thickness near the Tripura fold-belt and Bengal Basin varies within ∼36–40 km. The study reveals the existence of a shallow mantle discontinuity (Hales discontinuity) at a variable depth range of ∼54–78 km characterized by a step increase (∼7.5–11 %) in shear wave velocity observed in the inverted models. The mineralogical phase transformation from spinel to garnet is considered as the origin of this discontinuity. The shallow depth of the discontinuity indicates an increase in upper mantle temperature which conforms to the high geothermal gradient reported in the region. The variation of depth of the discontinuity can be interpreted in terms of the addition of Cr+3 that shifts the spinel-garnet stability field to higher depths whereas Fe+2 shifts it to lower depths. Despite the high temperature in the upper mantle, the observed low Vp/Vs ratio (1.65–1.75) below the Hales discontinuity can be explained by the presence of a high fraction of orthopyroxene. [ABSTRACT FROM AUTHOR]