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Tsunamis are rare events involving several complex physical phenomena. Due to this complexity and the relative scarcity of observations, tsunami research makes extensive use of numerical simulations. For seismogenic tsunamis, the source is often modeled as an instantaneous sea‐floor displacement (IS), while the tsunami propagation and inundation is computed through a shallow water approximation (SW). Here, we investigate what is the best tsunami inundation modeling strategy for different realistic earthquake source size and duration. We use 1D earthquake‐tsunami coupled simulations of large M > 8 earthquakes in Tohoku‐like subduction zone to test for which conditions the IS and/or the SW approximations can simulate with enough accuracy the tsunami evolution. We use as a reference a time‐dependent (TD), multi‐layer, non‐hydrostatic (NH) 1D model. Source duration, and size, are based on 1D dynamic rupture simulations with realistic stress drop and rigidity. We show that slow ruptures, generating slip in the shallow part of subduction zones (e.g., tsunami earthquakes), and very large events, with an along‐dip extent comparable with the trench‐coast distance (as occurs for megathrust events) require a TD‐NH modeling, especially for regions with steep coastal bathymetry. Conversely, deeper, higher stress‐drop events can be modeled through an IS‐SW approximation. We finally show that: (a) steeper bathymetries generate larger runups and, (b) a resonant mechanism emerges with runup amplifications associated with larger source size on flatter bathymetries. These results, obtained with 1D modeling, can serve as a guide for the appropriate 2/3D simulation approach for applications ranging from fundamental tsunami science to computational‐intensive hazard assessments. Plain Language Summary: In the last two decades, tsunamis originated by large earthquakes have generated major damage and, according to the World Health Organization, more than 250 k casualties (more than 200 k due to the 2004 Indian Ocean tsunami). Strategies to quantify and mitigate the associated risk are based on numerical simulations of the physical processes regulating the generation, propagation of the waves and subsequent flooding on the coast. These simulations require significant computational resources. To make simulations more affordable, numerous approximations are introduced that need to be tested. In this work, we studied which earthquakes, depending on the speed at which they deform the sea bottom when they trigger a tsunami, and on how big they are, require a more detailed modeling approach, and which ones, instead, might be accurately simulated through approximated approaches. We also show how such findings are related to different bathymetric characteristics near the coast and inland, which may enhance or reduce the tsunami effects. Key Points: Slow and large ruptures (e.g., tsunami earthquakes and megathrust) require a time‐dependent, non‐hydrostatic modelingDeeper, high stress‐drop earthquakes might be modeled through an instantaneous source, shallow water approximationInundation depends on bathymetric features: larger inundations on steeper depth gradients and resonant runup amplifications are observed [ABSTRACT FROM AUTHOR]

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Acoustic waves generated by seismic waves contain information on the internal structure of planets, and can be sensed by pressure sensors onboard high-altitude balloons. To identify the various contributions (infrasound signal, noise, balloon response, etc.) in such pressure records, a full waveform modeling is implemented and completed by infrasound ray tracing and additional data analysis. Here, we analyze the Stratéole-2 pressure data associated with two earthquakes (Garcia et al. Geophys. Res. Lett. 49(15):e98844, 2022) and compared these to full waveform simulations by SPECFEM2D-DG-LNS software. Even if our simulations do not precisely reproduce the waveform observed in the frequency range [0.05, 0.3] Hz, we show that the waveform presents more sensitivity to quake and internal structure parameters than to atmospheric structure, and that seismic surface wave dispersion is observed in balloon pressure records. The long-duration pressure oscillations observed after the main infrasonic signal cannot be fully reproduced by our one-dimensional input model even when source time function complexity and aftershocks are considered. These features are ascribed mainly to the complex vertical ground movements below the balloon and partly to late secondary infrasound arrivals excited by the interactions of seismic waves with the topography. These results enhance the advantages and limitations of quake-related infrasound observations on board terrestrial and planetary balloon platforms. [ABSTRACT FROM AUTHOR]

Measurements of magnetic fields near seismic sources during solar flares are vital for understanding the dynamics of solar activity. We used spectropolarimetric observations of the X17.2/4B solar flare on 28 October 2003, over a wavelength interval of 43 Å, including the D3, D2, D1, and Ni I 5892.88 Å lines, to analyze the Stokes I ± V profiles. Effective magnetic fields within 0.5–1.5 kG were measured in the D1, D2, and D3 lines at different flare locations, with the photospheric Ni I 5892.88 Å line showing a weaker field of below 0.5 kG. The D3 line showed rapid plasma descents of up to 11 km/s, in contrast to the slower velocities within 2.3 km/s observed in other lines. The differing amplitudes in the I + V and I − V profiles indicated potential non-Zeeman polarization effects. Secondary Stokes V peaks were also detected up to 8 Å from the D3 emission core. Significant altitudinal inhomogeneity in the magnetic field strengths was detected, possibly indicating the local magnetic collapse, facilitating the Lorentz-force driven mechanism of the seismic source excitation. [ABSTRACT FROM AUTHOR]

Shear wave velocity is a fundamental parameter in determining geological structures and soil characteristics for geotechnical and earthquake engineering studies. In shallow seismic data acquisition, shear wave is generated by various seismic sources. Although the data quality is affected by the choices of the seismic source, applying highly efficient sources is sometimes limited for some users and by the budget available for a project. Therefore, this work aims to design and develop an effective shear wave seismic source as an alternative for shallow seismic surveys. The developed source consists of 4 main parts, including base plate, activated mass, lifting and shooting system, body and transportation system. It is simply operated by lifting an activated mass with a sling and puller to the armed position. Under this condition, an attached spring is under compression and the maximum potential energy is stored. When the mass is released and horizontally hit the base plate, shear wave is generated by the momentum and energy transferred from the base plate into the ground. To evaluate the source capability, a comparison of the conventional and the developed source was performed at a test site. The recorded data were compared both in qualitative and quantitative manners based on the signal-to-noise ratio, energy and frequency content, signal penetration, and repeatability. It was found that signal energy generated by one blow of the developed source is equivalent to approximately three-fold of the conventional source. There is a remarkably higher repeatability from the developed source than that from the conventional source. Moreover, it is easy to operate, portable, and minimizes required man power. Overall, the new shear source is suitable and has potential application for shallow seismic surveys. [ABSTRACT FROM AUTHOR]

The lack of clarity regarding slip distribution within heterogeneous rupture areas has a significant impact on characterizing the seismic source and the role of heterogeneities in determining ground motion. One approach to understand the rupture process is through dynamic simulations, which require substantial computational resources, thereby limiting our comprehension of seismic rupture processes. Consequently, there is a need for methods that efficiently describe the spatial complexities of seismic rupture in a realistic manner. To address this, the statistics of real self-arrested ruptures that conform to the asperity criterion are investigated. This research demonstrates that power law distributions can describe the final slip statistics. Regarding the computational efficiency, a simple heterogeneous energy-based (HE-B) method is proposed. The HE-B method is characterized by the spatial correlation between the rupture parameters, such as the final slip or the rupture velocity, and the distribution of residual energy which determines the zones where the rupture could occur. In addition, the HE-B method defines the rupture area in those zones of the fault where the coupling function exceeds the energy required for rupture initiation. Therefore, the size of the earthquake is directly influenced by the distribution of coupling within faults. This method also leads to the successful reproduction of the statistical characteristics of final slip and generates slip rates that match the kinematic behavior of seismic sources. Notably, this kinematic rupture simulation produces seismic moment rates characterized by f−1{f}^{-1} and f−2{f}^{-2} spectra with a double corner frequency. Finally, it is observed that the maximum fracture energy value within the ruptured area is strongly correlated with both the magnitude and peak seismic moment rate. Thus, by employing this method, realistic rupture scenarios can be generated efficiently, enabling the study of spatial correlations among rupture parameters, ground motion simulations, and quantification of seismic hazard.

Liquefaction is soil condition associated with the drastic increase in pore water pressure of uniform sandy soil due to an enormous earthquake. Therefore, this study aimed to investigate the correlation of liquefaction potential with excess pore water pressure ratio in nine boreholes located at Kretek 2 Bridge area using empirical and numerical methods. Liquefaction potential was estimated based on a semi-empirical method simplified by Idriss and Boulanger (2008), and safety factor (SF) value of 1.0 was used to represent the existence of its potential. The result showed that liquefaction potential was dominant at depths of 1.5 to 6.0 m, with the exception of BH-9 with 16.5 m and BH-4. Furthermore, the excess pore water pressure ratio was estimated using empirical method developed by Yegian and Vitelli (1981) as well as Serafini and Perlea (2010). Numerical analysis was also conducted for comparison purposes and the process focused on using Deepsoil v7.0 to generate excess pore water pressure by considering soil conditions and dominant seismic sources in Kretek 2 Bridge area. The result showed that the ratio of excess pore water pressure was greater or equaled 0.8. Both empirical and numerical methods produced similar values for BH-1, BH-2, BH-8, and BH-9 at a depth of 1.5-3.0 m, 3-4.5 m, 3.0 m, and 16.5 m, respectively. This showed a correlation between excess pore water pressure ratio and liquefaction potential values at the same depth. However, numerical method tended to overestimate the ru value, necessitating the use of empirical method to obtain a more reliable result. [ABSTRACT FROM AUTHOR]

Liquefaction is soil condition associated with the drastic increase in pore water pressure of uniform sandy soil due to an enormous earthquake. Therefore, this study aimed to investigate the correlation of liquefaction potential with excess pore water pressure ratio in nine boreholes located at Kretek 2 Bridge area using empirical and numerical methods. Liquefaction potential was estimated based on a semi-empirical method simplified by Idriss and Boulanger (2008), and safety factor (SF) value of

In this paper, a new geometric inversion method is proposed for obtaining the elastic parameters of an anisotropic focal regions More precisely, the eigenvalues of a vertical transversely isotropic elasticity tensor of a focal region are inverted up to a constant for a given only one moment tensor with the accuracy depending on the strength of anisotropy. The reason for using only one moment tensor is that although there might occur several earthquakes in the same focal region, the orientation of the sources is similar to each other. Hence, one cannot obtain independent equations from each earthquake in order to use them in the inversion of elastic parameters of the focal region. Moreover, this method can be applied for real‐time inversion once the moment tensor of an earthquake is evaluated. The inversion method relies on the geometric fact that a moment tensor can be written as a linear combination of the eigenvectors of the anisotropic focal region's elasticity tensor. Then, in the inversion, we use the fact that each coefficient of this unique decomposition is proportional to the eigenvalues of the focal region's elasticity tensor. Two approximations are used in this inversion method, in particular for the potency and the source orientations. The strength of anisotropy of the focal region determines how accurate these approximations are, and, hence, it also determines the resolutions of the inverted eigenvalues. Because of the anisotropy of the focal region, the errors in the inversion do depend on orientations of the dip and rake angles but not on the strike angle since the focal region is vertically transversely isotropic. The accuracy of the inversion for the five parameters of vertical transversely isotropic is shown for every 10°‐gridded orientation of the dip and rake angles on the stereographic projection. The results are very promising along some orientations as shown in the figures. The last section of the paper deals with the inversion of eigenvalues, up to a constant, for a given set of moment tensors; not by using only one moment tensor. It turns out that the best fit corresponds to the average of inversions obtained for different orientations of the sources. [ABSTRACT FROM AUTHOR]

It is widely recognized that since the Early–Middle Pleistocene, the Messina zone, the site of strong earthquakes, has undergone extension, but the geodynamic context which determined this deformation is still a matter of debate. This work suggests that such a tectonic event was caused by the interaction of northern Calabria with the continental Adriatic domain. The suture of that consuming boundary produced major changes in the microplate mosaic and the related kinematic pattern in the Southern Italian zones, which was triggered by the activation of the Sibari and Vulcano faults. In the new context, the Peloritani belt sector, dragged by the Hyblean block, rotated clockwise and then moved northward, causing its divergence from southern Calabria. The normal faults which have accommodated that separation may be the main seismogenic source in the Messina Strait. [ABSTRACT FROM AUTHOR]

The geological effects of the Khubsugul earthquake of January 12, 2021, with Mw = 6.7, which became the strongest in the Khubsugul region during the instrumental stage of seismological observations, are studied and mapped. Using the ESI-2007 scale, the epicentral zone with intensity VIII is contoured. The primary seismic rupture is represented by the right-lateral strike–slip with a displacement amplitude up to 20 cm, which renewed the Late Holocene tectonic scarp on the western side of the Khubsugul rift basin. The dynamics of rupturing in the Late Holocene indicates the gradual expansion of the basin due to the destruction of the adjacent mountain range. The data of satellite interferometry and seismological observations are in good agreement with the results of the field studies, which allows considering the delineated region of maximum shaking as a projection of the upper part of the source zone onto the surface. [ABSTRACT FROM AUTHOR]

We have examined the tsunami hazard in the Bering and Chukchi seas by determining whether trans-oceanic tsunamis penetrate into these regions through the Aleutian Islands and Bering Strait. Results are based on numerical modeling of eight major far-field earthquakes in the North Pacific Ocean and one near-field earthquake that occurred in the Bering Sea region: the 1946 Aleutian, 1952 Kamchatka, 1960 Chile, 1964 Alaska, 1965 Rat Islands, 1957 Andreanof Islands, 2011 Tohoku, 2012 Haida Gwaii, and 2017 Commander Islands earthquakes. It was found that the Bering Sea was most affected by the 1960 tsunami caused by the Chilean earthquake of magnitude Mw 9.5. According to our numerical simulations, it produced tsunami waves with amplitudes up to 294 cm in the sea. For the next strongest event, the 1952 Kamchatka tsunami, the wave amplitudes were up to 146 cm. The 1964 Great Alaska earthquake (Mw 9.2) did not produce an intense tsunami in the Bering Sea because the long and narrow southwestern extension of the Alaska Peninsula sheltered the region from incoming tsunami waves. Modeling further shows that, in separate bays, tsunami waves formed by strong distant earthquakes could reach 1.5–2 m. Results show that the typical attenuation coefficient for the straits of the Aleutian Islands is 0.75, on average, while the corresponding coefficient of the Bering Strait is ~ 0.29. Based on these estimates, we conclude that tsunami penetration into the Arctic Ocean from remote sources in the Pacific is unlikely. Even for such powerful events as the 1960 Chilean tsunami, the tsunami wave amplitudes in the Chukchi Sea would not exceed a few centimeters. For the Bering Sea, the amplitudes from distant earthquakes can be significant. [ABSTRACT FROM AUTHOR]

Macroseismic observations can be useful to study pre-instrumental earthquakes when paleoseismological analysis are not viable for various reasons (e.g., erosion or lack of sedimentation). The analysis of the distribution of the macroseismic intensity data points and the reports about geological effects has been shown as a tool that may provide meaningful information to localize the fault source of a historical earthquake. Using this approach, we have studied two earthquakes in the Betic Cordillera (South Spain), the 1804 Dalías and the 1680 Málaga events, and we have used the 2011 Lorca earthquake as a test subject to calibrate the methodologies. During the calibration process, we also find the best performing combination of ground-motion models and ground-motion-to-intensity-conversion equations for generating seismic scenarios in this area. Even though the results for the Málaga earthquake were not conclusive, our methodology successfully identified the most likely source for the Dalías earthquake: a conjunct rupture of the Loma del Viento and Llano del Águila Faults.

In recent years, seismic wave effects caused by meteorite impacts have been widely observed. The meteorite impact event that occurred 66 million years ago is one of the most famous impact events in Earth’s history. The influences of the seismic wave field generated by this collision event on the solid Earth itself is worth exploring. Therefore, this study initially estimated the seismic source parameter information based on the multiring structure of the meteorite crater, and then simulates the seismic event. The results of this study provide a possible explanation for the formation of the Earth’s tectonic plates. The findings of this study suggest that the seismic wave field generated by the meteorite impact event 66 million years ago may have caused the destruction of the Solid Earth, leading to the formation of the boundary between the Indian Ocean and the Pacific Plate. Simultaneously, this study has important significance for inspiring the development of new geoscientific methods.

This work presents a macroseismic analysis of the AD 1755 Lisbon Earthquake-Tsunami event by means of the combination of intensity data derived from the EMS-98 scale and the ESI-07 scale (Environmental damage). About 600 records of secondary earthquake environmental effects (EEEs) for the whole Spain have been used to define intensities, focused on the SW portion of the Iberian Peninsula. The Spanish data have been complemented with 308 EEEs records from Portugal. The analyses indicate maximum intensities of X EMS-ESI along the Atlantic margin of the Iberian Peninsula with 76 records of Tsunami environmental effects (TEEs). An important amplification (VIII – VII) occurred all along the Guadalquivir basin and the adjacent Betic front at epicentral distances of 300–700 km. In these zones 55 records of ground effects (ground cracks, Liquefactions and slope movements) are catalogued. In the rest of the territory of the Peninsula the most widespread effects were hydrogeological changes with 505 records in Spain and 196 in Portugal (total 701 records) covering all the intensity levels. Increase of flow discharges in springs and elevation of water level in wells was the common groundwater response to seismic shacking, especially in SW Iberia. In this zone water elevation in wells was between 5 and 3 m and persistent increases of discharges long-lasting (several days to two months). Persistent discharges on springs were linked in 143 cases to important SW-NE crustal faults (e.g., Alentejo-Plasencia Fault). From the Intensity distribution the historic seismic scenarios are explored by means of the development of empirical ShakeMaps. These consider the three classical seismic sources proposed for this earthquake: Gorringe Bank (G); Marques de Pombal Fault (M) and Atlantic delamination beneath the Gulf of Cadiz (C). However, individually these seismic sources are too small and unable to generate the resulting seismic scenario depicted by the intensity map developed in this work, with onshore seismic accelerations (PGA) up to 0.82 g. These acceleration values and the great amplification experienced throughout the Guadalquivir basin (0.34–0.52 g) are only possible considering a combination of the three seismic sources (GMC Source) probably related to shallow subduction or lithospheric delamination beneath SW Iberia and the Gulf of Cadiz. This will suggest an NNE-SSW offshore rupture length of 350–360 km with an overall rupture area of c. 84,500 km2 resulting in an event magnitude 8.6 Mw calculated from empirical relationships. The results demonstrate the efficacy of these kind of approaches for better identifying and modelling seismic sources for historical events. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, the results of lidar monitoring of magmatic aerosol variation are presented. The lidar was installed in a hot dead-end tunnel at the end of the auxiliary adit of the Baksan Neutrino Observatory (BNO) of the Institute for Nuclear Research, Russian Academy of Sciences, which is located above the small magma chamber of the Elbrus Volcanic Center. A sharp (within ~30 min) threefold increase in the aerosol concentration in the hot tunnel was detected (October 28, 2019, 22:30 UTC). The analysis involved data on volumetric radon activity, air temperature, and humidity. A synchronous increase in temperature, humidity, and aerosol concentration in the tunnel, as well as their correlation with the deformation of the Earth's crust by tidal waves, which is monitored at the BNO with a laser strainmeter, was revealed. However, the threefold jump did not appear in these signals. The totality of data confirms the existence of a hot magma chamber at the base of Mount Andyrchi that was previously discovered by a small-aperture seismometer group. The assumption that the release of gases from the magma chamber could provide a jump in the concentration of aerosols without disturbing other parameters is discussed. [ABSTRACT FROM AUTHOR]

Seismic observations of underground nuclear explosions provide crucial data on source yield and depth that cannot easily be estimated from other geophysical methods. However, it is difficult to obtain reliable yield estimates for test sites for which we do not have direct seismic calibration experiments. To obtain source information from uncalibrated sites and paths, local and regional seismic records of six, proximal, declared underground nuclear explosions in North Korea are used to compute spectral ratios of narrow‐band waveform envelopes of body‐wave coda that remove path and site effects to reveal precise, relative source moment. The yields of these explosions are obtained from the observed source ratios by simultaneously fitting the classical source model of Mueller and Murphy (1971), https://doi.org/10.1785/bssa0610061675 to all event pairs. The source model provides an impressive fit to the observations considering that the P phase coda derived source spectral ratios did not require a prior knowledge of the source or regionally calibrated corrections to be applied to the data. However, the observed corner frequencies from S wave coda spectral ratios are lower than the source model predictions, but are well fit by models calculated using the corner frequency consistent with the Fisk conjecture. The results presented here provide novel constraints on the spectral distributions of the energy radiated by the sources of the DPRK test series, and allows for an independent evaluation of existing estimated source model parameters. Plain Language Summary: It is difficult to determine the size and depth of an underground nuclear explosion only using observations of the ground shaking caused by its detonation. Optimally the test site is first calibrated using a "ground truth" explosion with a known depth and size. However, for many sites of interest, such as the location of the six declared North Korean nuclear tests occurring between 2006 and 2017, this information is not available. In order to characterize these uncalibrated underground explosions, we use ground shaking measured by sensors located within ∼1,000 km of the test site to determine "coda spectral ratios." These coda spectral ratios use the measurements of two explosions which were recorded at the same seismic sensor, and both occurred at roughly the same location, to remove the changes in the wave caused by the rock, as the wave traveled through the Earth's crust from the site of the explosion to the location of the sensor. The resulting measurement is an estimate of the amount of energy created by the explosion for each frequency of vibrational wave that radiates out from the explosions. The size of these nuclear tests is then determined by fitting physical models of explosions to the derived data. Key Points: The P wave coda spectral ratios match the predicted source spectral ratios calculated using the Mueller and Murphy (1971), https://doi.org/10.1785/bssa0610061675 source model (MM71)The observed S wave corner frequencies are consistently lower than those predicted by MM71, and provide support for the Fisk conjectureThe coda spectral ratios obtained in this study are used to estimate new independent yield estimates of the North Korean tests [ABSTRACT FROM AUTHOR]

In this research paper, we have modelled the tsunami source of the 1970 Peruvian earthquake. The rupture geometry (of dimensions 150×75 km2) was obtained from the aftershocks distribution. The fault plane geometry was divided into 2 subfaults: the biggest (of 112.5-km length to the northern side) of normal fault plane and the smallest (37.5-km length to the south) of reverse fault plane, due to the seismic event had a complex rupture process. The slip was constrained from the tsunami waveform amplitudes and seismic moment using an iterative approach method, since a data inversion is impossible due to the scarcity of available tsunami data. The simulated vertical deformation field has a particular pattern, it is composed of 4 lobes of alternated uplift and subsidence, the maximum subsidence was 38 cm, and the maximum uplift was 57 cm. We have obtained a seismic moment of 8.92× 1020 Nm and the corresponding moment magnitude was Mw 7.9. The maximum slip was calculated in 1.59 m (reverse fault) and 1.32 m (normal fault). The simulated maximum tsunami height was 93 cm at Salaverry and 73 cm at Chimbote stations. [ABSTRACT FROM AUTHOR]

The application of fault-slip seismic sources is critical to the success of ground motion dynamic response analysis. Previous research established a finite seismic source to analyze stability in underground engineering. In this paper, a sophisticated numerical method based on the distinct element method (3DEC) is proposed to simulate the fault-slip seismic sources of an underground research laboratory (URL) exploration tunnel. Two indices, i.e., the peak ground velocity (PGV) and the strain energy density (SED), are used to analyze the sensitivity of the seismic source types, the seismic source radius, and the rupture velocities of the rock mass dynamic response. The simulation results indicate that a circular seismic source can be used so that the boundary produces a small singularity, with the seismic source having a remarkable influence on the PGV and SED. In addition, we consider that the rupture velocity is more suitable for engineering practices. A simulation method has been developed that allows the rock mass stability of a URL to be further explored. [ABSTRACT FROM AUTHOR]

It is widely recognized that since the Early–Middle Pleistocene, the Messina zone, the site of strong earthquakes, has undergone extension, but the geodynamic context which determined this deformation is still a matter of debate. This work suggests that such a tectonic event was caused by the interaction of northern Calabria with the continental Adriatic domain. The suture of that consuming boundary produced major changes in the microplate mosaic and the related kinematic pattern in the Southern Italian zones, which was triggered by the activation of the Sibari and Vulcano faults. In the new context, the Peloritani belt sector, dragged by the Hyblean block, rotated clockwise and then moved northward, causing its divergence from southern Calabria. The normal faults which have accommodated that separation may be the main seismogenic source in the Messina Strait.

Seismic-hazard analysis is based on the knowledge of the factors that configure the wave attenuation properties due to the loss of energy radiated away from the source (geometrical spreading and anelastic attenuation) and the site amplification due to surface geological conditions (the so-called site effects). Both factors can be separately investigated based on Generalized Inversion Techniques (GIT), through spectral decomposition of earthquake recordings in terms of Fourier Amplitude Spectra (FAS). In this study a parametric GIT algorithm, was applied in western Greece, allowing a simultaneous spectral decomposition of S-wave records in order to estimate parameters controlling seismic motion. The analyses provided a regional variation of the quality factor, Qs between 23—91, with a geometric mean value of 45, a distance dependent geometrical spreading attenuation factor gamma, γ, smoothly decreased between 12 and 200 km, from 0.98 to 0.77, as well as Site Amplification Factors for both horizontal and vertical components of 24 sites located in the study area. Moment Magnitudes, Mw and corner frequencies, fc, were computed for the examined earthquakes, indicating an increasing trend of stress drop, Δσ from ~ 6 to ~ 55 bar for Mw = 2.5 to 5.2. The estimated values of these parameters, are in good agreement with the corresponding ones based on other methodologies, concluding to the relevant low average logarithmic misfit (~ 0.17) between observed and synthetic FAS. Consequently, attenuation and site amplification factors computed in this study, can provide rational input parameters for stochastic S-wave simulations, improving thus deterministic seismic hazard assessment. [ABSTRACT FROM AUTHOR]

The invariants of the moment tensor such as its norm, eigenvalues and trace are closely related to the physical properties of the seismic source and the focal region, for example, seismic moment, radiation pattern, non‐double‐couple components. In this study, we investigate the relationship between these invariants and the eigenvalues and eigenvectors of the transversely isotropic elasticity tensor of the focal region. More specifically, we study how these invariants change as the source orientations vary with respect to the symmetry axes of the transversely isotropic elasticity tensor, by plotting these invariants on the stereographic net. Fortunately, one can plot them since they are independent of the strike of the fault when the focal region is a vertical transversely isotropic medium. Eigenvalues of the elasticity tensor control the invariants of the moment tensor; for instance, the ratio of the maximum and minimum norms achieved for some orientations of source is equal to the ratio of the two specific eigenvalues of the elasticity tensor. Moreover, the separation of the eigenvectors of the moment tensor from the eigenvectors of the source tensor is related to the deviation of the eigenvalues of the transversely isotropic elasticity tensor from the eigenvalues of the closest isotropic elasticity tensor. It is also found that this deviation is responsible for the percentages of non‐double‐couple components of the resulting moment tensor. This linear algebra point of view makes it easier to understand why and how the structure of the moment tensor changes for different orientations of sources. [ABSTRACT FROM AUTHOR]

Seismic waves radiated by small crustal earthquakes are prone to multiple mode conversions caused by reflection and transmission at interfaces, and scattering by small-scale heterogeneities in the bulk of the medium. The goal of this study is to clarify the complex interplay between volume scattering and interface reflections in crustal waveguides and how it will impact the crustal energy propagation. To carry out this task, we have incorporated a rigorous description of wave polarization in the context of Monte–Carlo simulations of the multiple-scattering process by introducing a five-dimensional Stokes vector. To shed light on the wave content of the regional short-period seismic wavefield, we investigate the asymptotic partitioning of seismic energy onto P, SV and SH polarizations in the coda, as well as the angular distribution of energy flux in the waveguide. In full elastic space, equipartition theory predicts that (1) the energy ratio between P- and S-wave energies tends to β 3 / (2 α 3) , (2) an equal distribution of energy among SV- and SH-waves and (3) that energy fluxes are isotropic. In the presence of interfaces, we find that the isotropy of the wavefield is systematically broken and that energy ratios are shifted to the detriment of P-waves and in favor of SV-waves in a non-absorbing medium. This implies that a residual polarization is preserved in the waveguide. Through an extensive parametric study, we illustrate in detail how the anisotropy of the wavefield, the partitioning ratios and the shear wave polarization depend on the crustal attenuation parameters. The role of the initial polarization at the source has also been examined. In the case of an explosion and a shear dislocation with equal magnitude, we find that the energy level in the coda can differ by more than one order of magnitude when the effect of crustal scattering becomes very weak compared to reflections or transmissions at interfaces. When comparing different shear dislocation mechanisms, we find that the energy level in the coda can differ by up to 60%. While equipartition, depolarization and coda normalization remain fundamental guides to our understanding of the coda, their application requires a good a priori knowledge of the attenuation properties of the crust. [ABSTRACT FROM AUTHOR]

We describe source and path attributes of the Next Generation of Ground-Motion Attenuation for Subduction zones (NGA-Sub) project relational database. The database contains 991 earthquakes between 1937 and 2016 that meet quality assurance standards and have assigned event types (mostly interface or intraslab). Data curation emphasized large magnitudes: 73% of events have M > 5 and 13 events have M > 8. Event attributes in the database can be broadly divided into those related to the moment tensor, those related to rupture surface geometry (referred to as finite-fault parameters), and categorizations by type (e.g. interface, intraslab) and sequence classification (mainshock, aftershock). Earthquake information and moment tensor parameters compiled from earthquake catalogs include event date and origin time, hypocenter location, seismic moment, and the strike, dip, and rake angles of nodal planes. Finite-fault parameters include along-strike length, down-dip width, and depth to top-of-rupture for one or more rectangles used to parameterize rupture surface geometry. These are modified from models in literature where available, and otherwise are simulated using procedures customized for subduction earthquakes. Rupture distance and other metrics are computed using finite-fault representations of sources, and (as applicable) are partitioned into forearc and backarc components. Forearc and backarc regions are defined based on volcano locations, and are assigned to events and sites. [ABSTRACT FROM AUTHOR]

Seismic intensity assessment in points of a macroseismic scale plays an important role for researching the seismic history of areas characterized by active seismicity, as well as for construction (and updating) of seismic zoning maps in various scales. Macroseismic scale points are generally referred to in construction standards applied in the majority of post-Soviet states. In our study aimed to model the macroseismic field of earthquakes, a large volume of macroseismic data on Central Asia was analyzed, and coefficients used in Blake–Shebalin and Covesligeti equations were aligned. This article presents a generalized dependence model of macroseismic intensity attenuation with distance. The model takes into account seismic load features determined by various depths of earthquakes. The ratios of small and big axes of the ellipse, that approximates real isoseists, are estimated with respect to seismic scale points, earthquake depths and magnitudes. The East Uzbekistan area is studied as an example to investigate whether seismic hazard assessment values may differ depending on a chosen law of seismic influence intensity attenuation with distance.

A prototype electromagnetic vibrator, referred to here as E‐Vib, was upgraded and developed for broadband hardrock and mineral exploration seismic surveys. We selected the iron oxide mine in Blötberget, central Sweden, for a test site in 2019 for the newly developed E‐Vib because of the availability of earlier seismic datasets (from 2015 to 2016) for verification of its performance for hardrock imaging purposes. The two‐dimensional data acquisition consisted of a fixed geometry with 550 receiver locations spaced at every 5 m, employing both cabled and wireless seismic recorders, along an approximately 2.7 km long profile. The E‐Vib operated at every second receiver station (i.e. 10 m spacing) with a linear sweep of 2–180 Hz and with a peak force of 7 kN. The processing workflow took advantage of the broadband signal generated by the E‐Vib in this challenging hardrock environment with varying ground conditions. The processed seismic section shows a set of reflections associated with the known iron oxide mineralization and a major crosscutting reflection interpreted to be from a fault system likely to be crosscutting the mineralization. The broadband source data acquisition and subsequent processing helped to improve signal quality and resolution in comparison with the earlier workflows and data where a drophammer seismic source was used as the seismic source. These results suggest new possibilities for the E‐Vib source for improved targeting in hardrock geological settings. [ABSTRACT FROM AUTHOR]

The number of gigaton‐sized iceberg‐calving events occurring annually at Greenland glaciers is increasing, part of a larger trend of accelerating mass loss from the Greenland Ice Sheet. Though visual observation of large calving events is rare, ∼60 glacial earthquakes generated by these calving events are currently recorded each year by regional and global seismic stations. An empirical relationship between iceberg size and MCSF, a summary measure of glacial‐earthquake size, was recently demonstrated by Olsen and Nettles (2019), https://doi.org/10.1029/2019JF005054. However, MCSF is known to be sensitive to choices made in modeling the seismic source. We incorporate constraints on the seismic source from laboratory studies of calving and test multiple source time functions using synthetic and observed glacial‐earthquake waveforms. We find that a simple, fixed time function with a shape informed by laboratory results greatly improves estimates of earthquake size. The average ratio of estimated to true peak force values is 1.03 for experiments using our preferred source model, compared with an average of 0.3 for models used in previous studies. We find that maximum‐force values estimated from waveform modeling depend far less on model choices than does MCSF, and therefore prefer maximum force as a measure of glacial‐earthquake size. Using both synthetic and real data, we confirm a correlation between maximum force and iceberg mass. Our results support the possibility of developing useful scaling relationships between seismic observables and physical parameters controlling glacier calving. Plain Language Summary: The Greenland Ice Sheet is losing ice mass. About half of that ice is lost when large icebergs break off, or calve, from the fronts of glaciers into the ocean. Knowing the sizes of these icebergs would be valuable, but iceberg calving is rarely captured on camera. However, the largest icebergs produce seismic signals when they calve, referred to as glacial earthquakes. We investigate the relationship between the size of an iceberg and the magnitude of the glacial earthquake it produces, building new models to describe the forces that generate a glacial earthquake. Previously, most details of the force evolution during iceberg calving were unknown. We use observations from laboratory experiments conducted using a plastic block in a tank of water, built to mimic the glacier‐ocean setting. We find that incorporating information from these laboratory experiments into our seismic model greatly improves estimates of earthquake size. Using our new models, we confirm a correlation between glacial‐earthquake magnitude and iceberg size, and show that our improved estimates are likely to be more realistic. Our results suggest that using seismic information to estimate iceberg size and related quantities is a promising path forward. Key Points: A physics‐based source model for glacial‐earthquake modeling improves recovery of seismic‐magnitude valuesMaximum force is less sensitive to model choices than MCSF and is preferred for describing glacial‐earthquake sizeA rapid force reversal during iceberg calving is the most important feature to capture in a glacial‐earthquake source model [ABSTRACT FROM AUTHOR]

Although destructive earthquakes have not occurred in the instrumental period except for the 30 October 2020 Samos earthquake (Mw = 6.6), the records show that there were significant earthquakes that caused great destruction in İzmir and its surroundings in the historical period. However, it is not yet clear which faults are causative for these earthquakes affecting İzmir and its surroundings. For this purpose, it has been attempted to determine new geological, seismological and environmental data by examining a large number of original sources, records and old international earthquake catalogs, other than the existing national catalogs used in seismicity studies in Turkey. In this context, a new local and updated historical earthquake catalog was prepared for İzmir and its immediate vicinity. The data obtained from the records show that the maximum intensity of some destructive historical earthquakes in the İzmir region was X. This means that the active faults in İzmir and its immediate vicinity have the potential to generate earthquakes of up Mw = 7.1 in the future. Details on historical earthquakes strengthen the possibility that these earthquakes may have been generated by active faults located near the İzmir city settlement. The isoseismic maps created for the first time using historical data, point out that the highest seismic intensity in the 178, 1688 and 1778 A.D. earthquakes caused destruction in the İzmir city center and nearby settlements indicate that they were concentrated at a relatively small area in the Bay of İzmir, and tectonically in the hanging-wall of the İzmir Fault. In the most likely scenario, all these damages observed may be attributed to the western segment of the İzmir Fault (Balçova segment) since it was defined as the only seismic source around the İzmir Bay in the updated active fault map of Turkey, of course, these data should be verified by performing detailed paleoseismological studies. [ABSTRACT FROM AUTHOR]

On May 26, 2019, an unusual depth-intermediate focus earthquake, in the interior of the Nazca plate, shook the northern Peruvian jungle and caused the death of two victims. This earthquake was felt in almost all of Peru as well as Brazil, Ecuador and Colombia. The focal mechanism calculated is of the normal fault type (strike = 353∘, dip = 57∘, rake = − 99∘) for a focal depth of 114 km. The slip distribution was obtained through an inversion process of teleseismic waveforms. The maximum slip was 6.3 m, located around the central side of the fault plane. The moment magnitude calculated was Mw 8.0; the spectral analysis indicated a similar magnitude of Mw 8.0. The source time function indicates a multiple rupture earthquake, with the presence of several pulses of seismic energy release, with a total duration around 80 s. The rupture directivity was from the south to the north; we have assumed a propagation rupture velocity of 2.8 km/s. The modeled fault plane geometry has dimensions of 208×105 km2. The predicted vertical coseismic deformation field shows a pattern of mostly subsidence. [ABSTRACT FROM AUTHOR]

The generalized inversion technique (GIT) of earthquake recordings is a useful tool in retrieving seismic source spectra, attenuation path parameters and site transfer functions (TF). Further understanding of these three fundamental factors which control seismic ground motion constitutes one of the main challenges in seismology. Especially, the site TF estimation is an important objective that can significantly contribute to seismic hazard assessment. In this study, a parametric GIT algorithm (in MATLAB (The MathWorks, Inc., Natick, Massachusetts, United States, 2017)), based on the one proposed by Drouet et al. (Bull Seism Soc Am 98:198–219, 2008a), is developed, by introducing distance- and regional-dependent attenuation parameters for geometrical spreading and anelastic attenuation terms, respectively. This step is aimed at a more detailed investigation of attenuation path, anticipating to improve the knowledge of all three fundamental factors controlling seismic ground motion. The algorithm is based on a Gauss-Newton iterative inversion method, using initial reasonable model parameters. Source term is parametrically investigated for seismic moment and corner frequency, which can be simultaneously controlled with respect to stress drop. A synthetic dataset, approximating a simplified real dataset was inverted by the proposed inversion algorithm examining its computational validity. Four tests were implemented, with or without reference condition, providing encouraging results. The applicability of the algorithm is supported by the inversion of a real dataset which was also examined by Grendas et al. (Bull Earthq Eng 16:5061–5094, 2018) using a uniform attenuation model in GIT. Approximately 9% reduction of the misfit between real and computed data from the inverted model data is achieved, showing the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

We have kindly received the comments by Hamdache and Pelàez on our published paper (Hamidatou et al. 2019); This article will give us the opportunity to provide more explanation and clarifications on the methodology followed during our work. We find these comments and critiques helpful for our future works. However, most of them were generated from the misapprehension of the paper by the comment authors. These remarks were mainly based on (1) the misjudging of the seismic source zone model used in relation to the active faults in the study area, (2) suspecting that the probabilistic seismic hazard PGA values were wrongly quoted from their analyses in our work, and (3) the logic tree usage , for which we here provide further general clarifications. [ABSTRACT FROM AUTHOR]

We would like to make some comments on the paper by Hamidatou et al. (2019). Initially, these comments are motivated to reveal that, previous results on probabilistic seismic hazard analyses, some of them computed and published by our research group, are wrongly quoted in the paper by these authors. In our opinion, some other points are worthy of debate, mainly, but not only, the used seismic source zone model, the used logic-tree, and also the comparison of estimated values of peak ground horizontal acceleration (PGA) with previous results. [ABSTRACT FROM AUTHOR]

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Sparker and explosive-type marine seismoacoustic signal sources are described, which can be used to solve engineering seismic survey problems in water areas. The problem of surface wave excitation in water area conditions (moreover, in the presence of ice cover) is quite relevant due to the intensive development of surface-wave methods in land seismology. The paper presents the results of an in situ experiment in the ice conditions of Lake Ladoga, devoted to recording seismoacoustic signals in the water column (with hydrophones) and on shore (with a seismic receiver). Processing and analysis of experimental data demonstrated the possibility of applying the coherent integration procedure for a sparker impulse source in order to increase the signal-to-noise ratio of the initial hydroacoustic and seismic data. The waveforms of the signals received in the water column and on shore were obtained as the waves passed through a shore wedge in the presence of sheet ice. The coherence coefficient of signals generated by a sparker and airgun is estimated. The dependence of the signal-to-noise ratio on the number of summed pulses during coherent integration was analyzed. The results point to high quality of the sparker equipment developed at GEODEVICE and demonstrate the possibility in principle of using a sparker to generate seismic waves, including surface ones. [ABSTRACT FROM AUTHOR]

Underground seismic exploration is a technical assurance for the geological transparency of the mining face. However, seismic exploration with explosive seismic source has shortcomings such as acquisition difficulties and serious safety hazards. Besides, dynamic detection of the mining face with explosive source is challenging. To this end, the study proposes a supercritical CO 2 source based on the underground seismic geological condition of the roadway. The phase change blasting mechanism of the supercritical source was revealed, and the equivalent energy of the source was calculated. Additionally, a field test was also carried out. The results show that the seismic signals of the CO 2 source have clear P-waves, S-waves, and channel waves; the signal excited by the source has strong energy and rich frequency bands; the signal-to-noise ratio of single CO 2 source is high; and the attenuation images of transmitted channel wave excited by the source shows high resolution and the result is consistent with field validation data. CO 2 source can be used as a new source of underground in-seam seismic exploration and it also helps in reducing the dependence of explosive seismic source. Besides, the study can achieve early warnings of dynamic geological disasters in the working face and has the advantages of high efficiency, safe, low cost, and environmentally friendly. [ABSTRACT FROM AUTHOR]

In this research, we have conducted a numerical simulation to obtain the seismic source, coseismic deformation field, and the tsunami propagation of the great Lima-Peru 1940 earthquake and tsunami, based on macroseismic information and focal mechanism from the literature. The seismic dimensions of our preferred model were set at 162 km×71 km according to VIII isoseismal intensity. The slip distribution is homogeneous with a mean value of 2.7 m. The fault plane orientation was set at strike = 330∘, dip = 20∘, and rake = 90∘. The maximum simulated uplift was 1.27 m and the maximum subsidence was 0.36 m. Due to the proximity of the seismic source to the coast, the city of Huacho was uplifted around 11 cm. The fault plane of the 1940 earthquake was located in the updip near the coast. The maximum tsunami height simulated in Huacho was 1.80 m. We suggest that there is a high tsunamigenic potential near the trench to generate a shallow earthquake. [ABSTRACT FROM AUTHOR]