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To date, eight meteoroid impacts have been identified in the seismic record of NASA's InSight mission on Mars, occurring either within 300 km or beyond 3,500 km. We report the association of a high‐frequency marsquake, S0794a, with a new 21.5‐m‐diameter impact crater discovered at an intermediate distance of 1,640 km in the tectonically active Cerberus‐Fossae graben system. This impact enables the direct comparison between surface and subsurface sources, as well as providing the first data point in the critical gap between previous impacts, both in distance and crater size. Additionally, the location of this event necessitates a reassessment of assumed seismic raypaths that were thought to propagate along a slow crustal waveguide. We find that the raypaths instead penetrate and travel through the faster mantle, implying numerous identified marsquake epicenters should be relocated up to two times farther from InSight, with implications for seismically derived impact rates and regional seismicity. Plain Language Summary We have used global and high‐resolution orbital imaging to discover a fresh crater that appeared at the same time as one of the quakes detected by NASA's InSight lander. This means the seismometer detected a meteoroid strike rather than geological activity within the planet. We know the location of this impact as well as the timing of seismic energy arriving by different types of vibrations which traveled through Mars at different speeds. With this information, we can work out that these waves penetrated below the crust and into the mantle rather than being confined to the crust as previously thought. This new path of propagation leads us to question how far away other marsquakes were from the InSight lander. This has implications for both how often marsquakes occur as well as how frequently meteoroids hit Mars. Key Points We associate a new 21.5‐m Mars impact crater in the tectonically active Cerberus Fossae region with InSight's seismic event, S0794a The location derived seismically and via orbital imaging implies the impact's energy traveled significant distances through the mantle This challenges previous assumptions of a crustal waveguide, resulting in more distant locations for many high‐frequency marsquakes

The seismic vulnerability of bridges may be reduced by the application of Geotechnical Seismic Isolation (GSI) below the foundations of the columns and the abutments. However, the role of GSI on the seismic response of bridges has been limitedly examined in literature. Therefore, this research has been conducted to study the effect of applying GSI on the seismic response of bridges to address the aforementioned gap in knowledge. Advanced nonlinear dynamic three-dimensional finite element analyses have been conducted using OpenSees to study the influence of the GSI. The cases of traditional and isolated bridges subjected to earthquakes have been considered to assess the GSI effects. The results showed that the GSI reduces the seismic effect on the column while its effect seems to be less significant for the abutments. In addition, fragility curves for the traditional and isolated cases have been developed and compared to provide insights with a probabilistic-based approach. The results of this paper provide a useful benchmark for design considerations regarding the use of GSI for bridges.

Anisotropy is ubiquitous in the Earth's crust, which causes the elastic characteristics of seismic waves to change with direction. The study of seismic wave anisotropy is of great significance to seismic exploration, prediction and geodynamics. As one of the sources of seismic anisotropy, in situ stress belongs to secondary anisotropy as common as the intrinsic and fracture-induced anisotropy, but it is often ignored among the sources of seismic anisotropy. Therefore, we focus on the study of seismic anisotropy under the influence of in situ stress using the nonlinear acoustoelasticity theory. Based on a horizontal transversely isotropic (HTI) model and the linear slip theory, the characteristics of azimuthal seismic reflection response in anisotropic media under horizontal in situ stress are discussed in this paper. Firstly, by using the quasi-linear relationship between stress and Tsvankin’s anisotropic parameters and the transformation relationship between anisotropic and fracture parameters in HTI medium, the elastic stiffness matrix of an HTI medium with the effect of horizontal in situ stress is established. Secondly, the reflection coefficient of PP-wave seismic data for a planar weak-contrast interface separating two weak-anisotropy and small-stress HTI half-spaces is derived using both the seismic scattering theory and the stiffness matrix under horizontal in situ stress, building the quantitative relationship between azimuthal seismic reflection characteristics and the model parameters, such as the background elastic parameters, the fracture parameters and the horizontal-stress-induced anisotropic parameters. Finally, the variation rules of azimuthal seismic reflection response characteristics of four elastic interfaces under different in situ stress conditions are analyzed. The results demonstrate that the seismic inversion for fracture parameters and horizontal-stress-induced anisotropic parameters is more favorable under the condition of large incident angle. In addition, the effect of horizontal in situ stress on the reflection coefficient depends on the second- and third-order elastic properties of the rock itself. Also, the established seismic PP-wave reflection coefficient equation has provided an alternative approach to calculate the magnitude of horizontal in situ stress.Article HighlightsA novel linearized PP-wave reflection coefficient is presented for HTI media with the effect of horizontal in situ stressThe response law of azimuthal seismic reflection characteristics induced by horizontal in situ stress is demonstratedA simple inversion method is provided to calculate the magnitude of horizontal in situ stress

This paper illustrates the derivation of an empirical fragility model for residential unreinforced masonry (URM) buildings, calibrated on Italian post-earthquake damage data and compatible with the key features of the Italian national seismic risk platform. Seismic vulnerability is described by fragility functions for three vulnerability classes, then refined based on the building height. To this aim, a clustering strategy is implemented to merge predefined building typologies into vulnerability classes, based on the similarity of the observed seismic fragility. On the other side, a specific procedure is built up to determine the vulnerability composition of the exposed URM building stock, starting from national census data. The empirically-derived model was implemented into the national seismic risk platform and used, together with other vulnerability models, for assessing seismic risk in Italy. The results presented in this paper, consisting of refined typological fragility curves and fragility curves for vulnerability classes, can be also exploited for estimating both expected seismic damage and risk in sites with similar seismic hazard and building inventory.

Microcracks in geomaterials cause variations in the elastic moduli under applied strain, thereby creating seismic wave velocity variations. These are crucial for understanding the dynamic processes of the crust, such as fault‐zone damage, healing, and volcanic activities. Solid earth tides have been used to detect seismic velocity changes responding to crustal‐scale deformations. However, no prior research has explored the characteristics of the seismic velocity variations caused by large‐scale tidal deformation. To systematically evaluate the tidal response to velocity variations, we developed a new method that utilized the flexibility of a state‐space model. The tidal response was derived from hourly stacked noise autocorrelations using a seismic interferometry method throughout Japan. In particular, large tide‐induced seismic velocity changes were observed in the low S‐wave velocity region of the shallow crust. Overall, the tidal responses of velocity variations can provide new insights into the response mechanisms of the shallow crust to applied strain. Plain Language Summary Rock deformations can open or close microcracks in rocks along with varying their elastic moduli under an applied strain. The temporal variations in the elastic moduli of rocks alter the seismic wave velocity, which can be monitored to provide information on the strain applied to the crust. This is crucial for understanding the geological processes in fault zones and volcanic regions. To utilize the seismic velocity variations for monitoring how much the Earth's structure deforms, the response of the seismic velocity to the deformations must be assessed. The deformation of the Earth's surface caused by lunar and solar gravity, called solid Earth tides, has been used to study seismic velocity variations in response to crustal deformation. However, only a limited number of regions have been studied for the tidal response of the seismic velocity, and the characteristics of its variations caused by tidal deformation were not yet apparent. This study measured the tidal responses to seismic velocity variations throughout Japan with reliable estimations. Notably, the tide‐induced seismic velocity variations tend to increase in the low S‐wave velocity region. Overall, these results provide new insights into the response mechanisms of the shallow crust to deformations. Key Points The spatial distribution of seismic velocity changes caused by tides was determined using a dense network of seismic stations in Japan The tidal response of velocity variations was extracted from ambient noise using an extended Kalman filter with a Maximum Likelihood method Strain‐velocity sensitivities tend to increase at a low S‐wave velocity in the shallow crust

Seismic surveys along subduction zones have identified anomalously high ratio of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust that are possibly due to the presence of pore water. Such interpretations postulate that the pore structure is homogeneous at the scale of the seismic wavelength. Here we present the first statistical evidence of a heterogeneous pore structure in oceanic crust at scales larger than laboratory samples. The spatial correlation of measured bulk density profiles of the crustal section of the Samail ophiolite suggests that the pore structure is heterogeneous at scales smaller than ∼1 m. Wave‐induced fluid flow cannot follow the loading during the seismic wave propagation at this estimated heterogeneity, which implies that fluid‐filled microscopic pores and cracks have a limited impact on the observed high VP/VS anomalies in the subducting oceanic crust. Large‐scale cracks may therefore play an important role in shaping these anomalies. Plain Language Summary Seismic studies along subduction zones have identified unusually high ratios of P‐ to S‐wave velocity (VP/VS) in the subducting oceanic crust, which indicates the presence of water‐filled cracks and pores. The close link between pore water and local seismic activity highlights the importance of quantitatively interpreting these seismic anomalies in terms of pore characteristics. Previous interpretations have assumed that the microscopic pore structure is quite homogeneous, even at macroscopic scales as large as the seismic wavelength. However, our analysis of a bulk density profile of the crustal section of the Samail ophiolite, Oman, which is a fossilized oceanic plate preserved on land, indicates that the pore structure is more heterogeneous than previously assumed. This means that the fluid flow within the unit volume that represents the macroscopic physical properties of the rock cannot follow the wave‐induced loading during seismic wave propagations. This results in a relatively small impact of water on the seismic velocity, as inferred from theoretical models that predict the effective elastic properties of rock containing fluid‐filled cracks. Therefore, microscopic cracks may not have a large impact on the high VP/VS values of subducting oceanic crust, whereas large‐scale cracks may play a more significant role. Key Points The bulk density of the crustal section of the Samail ophiolite is more spatially heterogeneous than previously assumed The effect of fluid‐saturated microcracks on low‐frequency seismic velocities is modeled as an unrelaxed condition for this heterogeneity The high VP/VS anomaly in the subducting oceanic crust can be explained by both microcracks and large‐scale cracks

Despite the high detection level of the Italian seismic network and the risk associated with its fault networks, Central‐Southern Italy has no unique geophysical model of the crust able to illuminate its complex tectonics. Here, we obtain seismic attenuation and scattering tomography models of this area; both reveal high attenuation and scattering anomalies characterizing the entire Apenninic Chain and related to its East‐ and West‐dipping extensional Quaternary tectonic alignments. Fault‐associated fractured zones become preferential ways for circulating and degassing high‐attenuation CO2‐bearing fluids. A previously undetected fluid source area is a high‐attenuation volume below the Matese complex, while a similar smaller anomaly supports a fluid source near L'Aquila. The most prominent low attenuation and scattering volumes reveal a locked aseismic zone corresponding to the Fucino‐Morrone‐Porrara fault systems, representing a zone of significant seismic hazard. Plain Language Summary Geophysical methods are the most used tools for imaging the subsurface. Still, their resolution and reliability depend on the amount of good‐quality data and the sensitivity of the technique used for the target structures. Improvements in the seismic detection infrastructures of the last decade allow imaging zones characterized by sparse seismicity, like Central‐Southern Italy. Once combined with these data, new imaging techniques targeting attributes with higher sensitivity to stress and fluid saturation provide unprecedented resolution on tectonic interactions and fluid sources in this area. Here, we measured and mapped in 3D the energy lost by seismic waves during their propagation. Our results show a high‐attenuation volume elongated in the direction of the Apenninic Chain and particularly intense in Southern Italy, mapping fluid‐filled fracturing and a fluid source likely coinciding with the Matese area. The principal normal and reverse faults in the area control high‐attenuation zones. The most prominent low attenuation and scattering volume marked locked areas with low seismic energy release, suggesting them as the zones of stress accumulation. Key Points Scattering and attenuation tomography image the tectonics of the Apennine Mountain Belt Chain High‐attenuation anomalies mark crustal sources of CO2 following major structural alignments A high‐attenuation/high‐scattering volume reveals an extended fluid source beneath the Matese Mountains

Maseve Mine is located in the western limb of the Bushveld Complex, recognized as the largest layered igneous intrusion in the world. The study shows results from surface (SP1, SP2, and SP3) and tunnel (T3a, T3b, and TP4b) reflection seismic profiles, totaling 4150 m. Tunnel seismic data were acquired using a seismic landstreamer and spiked geophones with 5 m receiver and shot spacing, as well as a sledgehammer for shots due to space constraints and safety. The profiles, 10–50 m above mineral deposits, crossed major geological structures. Surface seismic profiles used cabled systems and wireless sensors with 5 m and 10 m receiver spacing, respectively, and a 500 kg drop hammer as a source with 10 m shot spacing. Despite high noise levels from mine infrastructure and power cables, a careful processing workflow enhanced target reflections. Interpretation was constrained using borehole data, geological models, and 2D/3D seismic modeling. The processed data exhibit gently dipping reflections associated with faults and dykes, imaging the target mineralization (Merensky Reef and Upper Group 2) and a possible extension. Tunnel seismic experiments demonstrated the application of seismic methods using in-mine infrastructure, while surface experiments proved efficient, illustrating small-scale seismic surveys’ capability to image the subsurface, adding value in active mining environments for exploration with cost-effective seismic equipment.

Attenuation exists in seismic wave propagation in subsurface layers, and relatively high attenuation occurs in oil-bearing reservoirs. Inversion of frequency components of observed seismic data generates values of attenuation factor 1/Q, which produces potential results for determining oil-bearing reservoirs. Beginning with expressions of seismic wave velocity in attenuating media, we involve P-wave maximum attenuation factor to rewrite P-wave velocity driven by an attenuating rock physics model, and we also employ an empirical relationship between P-wave attenuation factor and S-wave attenuation factor to express S-wave velocity in terms of P-wave maximum attenuation factor. Using the derived P- and S-wave velocities, we extend Zoeppritz equations to compute reflection coefficient for an interface separating two attenuating media. Under the assumption that contrasts in elastic properties of two media across the interface are small and the background attenuation is weak, we propose a linearized reflection coefficient of PP-wave as a function of contrasts in elastic parameters (i.e., P-wave velocity, S-wave velocity and density) and attenuation factor, and expression of elastic impedance (EI) is also presented. Based on the EI, we demonstrate an approach of estimating elastic parameters and attenuation factor from frequency components of partially incidence-stacked seismic data, which is implemented as a two-step inversion involving the prediction of EI datasets using a model-based damping least-squares algorithm and nonlinear inversion for elastic parameters and attenuation factor. Noisy synthetic seismic data generated using the extended Zoeppritz equations are employed to verify the robustness and stability of the proposed inversion approach. Applying the proposed approach to a real dataset acquired over an oil-bearing reservoir, we obtain convincing results of P-wave velocity, S-wave velocity, density and attenuation factor, which can reasonably match corresponding well log data.

Most international design standards prohibit or necessitate alternative seismic analysis and design for building frames having vertical irregularities. Nevertheless, the irregularity quantifiers provided by design guidelines and research studies do not appear to be strongly correlated with seismic impact risk. It is universally believed that regular buildings have a strong fundamental mode contribution to their seismic behaviour, and as the irregularity of the structure increases, the participation of higher modes increases. Four types of vertically irregularity buildings have been chosen in this study; Geometric Irregularity (GI), In-Plane Discontinuity (ID), Stiffness Irregularity (SI), and Mass Irregularity (MI). This study attempts to investigate the correlation between the regularity index (RI) with respect to seismic resilience index (SRI), seismic vulnerability index (SVI), and fragility functions for the selected buildings using non-linear dynamic and static analysis. The results of seismic risk analysis including (SVI, SRI, and fragility function) shows building frame with in-plane discontinuity (ID) to be more vulnerable and the highest risk among the selected structures. However, the outcomes of the regularity index clarifies that the geometric irregularity (GI) is the most irregular structure, followed by in-plan discontinuity (ID) frame structure. On the other hand, the geometric irregularity building performs even better than the regular building. Eventually, the framing sequence of the structural types in terms of their seismic resilience and their ability to withstand seismic movement are consistent with the seismic vulnerability index and the fragility functions (ID < SI < MI < R < GI). Accordingly, to regularity measures, the SRI does not correlate with the regularity index, as well as with SVI, and lastly with the Vulnerability Index obtained from the Nonlinear-Static Analysis (NL-SA), VI NLSA .