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We have observed both minor‐arc (R1) and major‐arc (R2) Rayleigh waves for the largest marsquake (magnitude of 4.7 ± 0.2) ever recorded. Along the R1 path (in the lowlands), inversion results show that a simple, two‐layer model with an interface located at 21–29 km and an upper crustal shear‐wave velocity of 3.05–3.17 km/s can fit the group velocity measurements. Along the R2 path, observations can be explained by upper crustal thickness models constrained from gravity data and upper crustal shear‐wave velocities of 2.61–3.27 and 3.28–3.52 km/s in the lowlands and highlands, respectively. The shear‐wave velocity being faster in the highlands than in the lowlands indicates the possible existence of sedimentary rocks, and relatively higher porosity in the lowlands. Plain Language Summary The largest marsquake ever recorded occurred recently and waves propagating at the surface, called surface waves, have been observed. Owing to the relatively large magnitude (i.e., 4.7 ± 0.2) of this event, surface wave energy is still clearly visible after one orbit around the red planet. The shortest path taken by the wave propagating between the source and the receiver is located in the northern lowlands, near the boundary with the southern highlands (called dichotomy). The surface wave traveling in the opposite direction, following the longer distance between the quake and the seismic station, mostly passes through the highlands. Analyses of these two paths reveal that the average shear‐wave velocity is faster in the highlands than in the lowlands near the dichotomy boundary. This lower velocity in the lowlands may be due to the presence of thick accumulations of sedimentary rocks and relatively higher porosity. Key Points Analyses of the minor‐arc and major‐arc Rayleigh waves reveal different Martian crustal structures across the dichotomy boundary The average shear‐wave velocity is faster in the highlands than in the lowlands near the dichotomy boundary The lower shear‐wave velocity in the lowlands may be due to the presence of sedimentary rocks and relatively higher porosity

Underground voiding refers to the phenomenon that abnormal looseness, plate breakage, increase in porosity of underground medium lead to the formation of voids that decrease the stability of stratum and weaken the physical and mechanical properties. For example, road underground voiding will seriously affect the comfort and safety of vehicle driving. At present, the engineering geophysical prospecting technology is mainly used to detect the void area. In this paper, the elastic wave simulation method is used to study the response of the Rayleigh wave method to the underground void of the pavement. The response regularity is explored by adjusting the model parameters. The outdoor experiment is carried out according to the law parameters, and the effectiveness of the elastic wave for the detection of shallow surface voids is verified.

For the first time, we measured the ellipticity of direct Rayleigh waves at intermediate periods (15–35 s) on Mars using the recordings of three large seismic Martian events, including S1222a, the largest event recorded by the InSight mission. These measurements, together with P‐to‐s receiver functions and P‐wave reflection times, were utilized for performing a joint inversion of the local crustal structure at the InSight landing site. Our inversion results are compatible with previously reported intra‐crustal discontinuities around 10 and 20 km depths, whereas the preferred models show a strong discontinuity at ∼37 km, which is interpreted as the crust‐mantle interface. Additionally, we support the presence of a shallow low‐velocity layer of 2–3 km thickness. Compared to nearby regions, lower seismic wave velocities are derived for the crust, suggesting a higher porosity or alteration of the whole local crust. Plain Language Summary As never before on Mars, we measured the characteristics of seismic waves traveling along the Martian surface that carry information about the crustal structure at the InSight site. We combined these measurements with two other local‐scale independent observations to derive a consolidated model for the crust underneath the InSight lander. Our results suggest a Martian crust with 4 layers and, particularly, one thin layer of about 2 km thickness close to the surface. The crust‐mantle discontinuity was found at ∼37 km depth, where the sharpest change in seismic wave velocity is observed. Overall, the seismic wave velocities of the local Martian crust at the InSight site are lower than those derived in other regions on Mars, which suggests a higher porosity or local alteration. Key Points Rayleigh waves ellipticity was measured between periods 15–35 s at the InSight landing site using large seismic events, including S1222a A 4‐layer crust, including a shallow low‐velocity layer, is required to explain the ellipticity, receiver functions and P‐wave lag times Low crustal velocities are derived for the InSight site, which may be due to high porosity or heavy alteration at local scale

Based on the analytical and numerical solutions as well as unexpected observed damages to the buildings and long-span structures in the epicentral zone of large shallow earthquakes, structural engineers have concluded that coseismic vertical ground motion play a major role in the damages. Recent researches have revealed the generation of high frequency Rayleigh wave with large amplitude in the epicentral zone of shallow earthquakes. Further, there is meta-response of a building at its longitudinal resonance frequency as compared to flexural resonance frequency during interaction with the Rayleigh waves. This paper presents the physics behind Rayleigh wave generation in the homogeneous half-space due to an incident SV-wave at the free surface and numerical quantification of variation of dominant frequency and spectral amplitudes of the generated Rayleigh waves with focal depth, Poisson's ratio and the rise-time of the point earthquake. It is concluded that the coupling of evanescence P-wave with the critically reflected SV-wave at/just after the critical point generates Rayleigh waves. Further, generation process is not immediate just after the critical point, but, it occurs over a span at least equal to one wavelength. A relation is established between depth of point earthquake and dominant wavelength of Rayleigh wave and this relation is unaffected by the change of Poisson’s ratio, rise-time and depth of point earthquake source. There is an exponential decrease of percentage conversion of the critically incident SV-wave energy in to the Rayleigh wave energy with an increase of focal-depth. Further, this percentage conversion increases with decrease of Poisson’s ratio and an increase of rise-time of the earthquake.

The Himalayas is currently rising due to the collision of the Indian and Asian plates and hosts frequent earthquakes, some of which are devastating, such as the 2015 Mw7.8 Gorkha earthquake. Despite the importance of deep dynamic processes to understand the uplift of the Himalayas and the occurrence of large earthquakes, it remains limitedly constrained due to the lack of a detailed three‐dimensional subsurface image under this region. Here, we construct new models of shear‐wave velocity and radial anisotropy down to the 150 km depth from Rayleigh‐ and Love‐wave tomography in the Nepal Himalayas. We find that the 2015 Gorkha earthquake and its main aftershock occurred in a velocity contrast that is presumably interpreted as Main Himalayan Thrust (MHT). A duplex structure, imaged as relatively high velocities, is inferred to exist above MHT under the Lesser Himalayas. This duplex shows heterogeneous features along the strike of the Himalayas that may control the rupture behavior during the occurrence of a large earthquake. Additionally, a low‐velocity anomaly is observed at depths from Moho to 100 km under the Lhasa Terrane and north of the Himalayan Terrane between 85° and 88°E. We interpret this low‐velocity anomaly to be likely caused by mantle upwelling resulting from either possible Indian slab tearing, or northward subduction of the Indian plate. If this is the case, the north‐south trending rifts that situate within the dispersal of the low‐velocity anomaly are probably associated with the mantle upwelling. This study provides a new independent constraint on the geometry of the MHT system and deep dynamic processes occurring in the Nepal Himalaya. Plain Language Summary The 2015 Mw7.8 Gorkha (Nepal) earthquake caused great damages to property and lives. It is widely suggested that the motion of a megathrust (i.e, the Main Himalayan Thrust (MHT) is responsible for the large earthquake. In order to understand the geometry of this thrust system and associated deep dynamics, in this study we constructed a three‐dimensional subsurface image of the Nepal Himalayas using surface wave that travels at the surface of the Earth. Our seismic image, together with previous studies of coseismic slip distribution, reveals that rupture behavior of the 2015 Gorkha earthquake and its main aftershock is controlled by the heterogeneous duplex structure (i.e., a system of imbricate thrust faults) of the megathrust. Additionally, we offer seismic velocity evidence for the occurrence of asthenospheric upwelling beneath the north of the Himalayan Terrane between 85° and 88°E that is likely linked with the variable MHT geometry along the strike of the Himalayas and surface exposed north‐south trending rifts. This study provides a new independent constraint on the geometry of the MHT system and deep dynamic processes occurring in the Nepal Himalayas. Key Points New lithospheric‐scale shear‐wave velocity and radial anisotropy models are constructed using surface‐wave tomography A duplex structure of Main Himalayan Thrust is imaged as relatively high velocities under the Lesser Himalayas, controlling earthquake rupture propagation Mantle upwelling is inferred to occur beneath north of the Himalayan Terrane between 85° and 88°E

The NE Tibet experienced complex and distinct basin developments and uplifts in different areas. However, the reasons for such distinct surface deformation and their relationship to deep crustal geodynamic processes are not well understood. Here, we obtain a crust model of NE Tibet by jointly inverting Rayleigh wave ellipticity and phase velocity. Our results reveal that deep crustal strength contrasts across NE Tibet play an important role in controlling basin development. Extrusion of the significantly weak Qilian crust is obstructed by rigid Alxa block, resulting in deep foreland basin with dramatic topographic step. In contrast, the relatively weak crust of Longzhong absorbs outward extrusion of NE Tibet within a wide transition zone, leading to small intermontane basins. Furthermore, the systematic thinning of basins from north to south around the western Ordos Block demonstrates the tectonic transformation from extension to compression due to expansion of NE Tibet since the late Miocene. Plain Language Summary In this study, we obtain a high‐resolution model of NE Tibet by jointly inverting Rayleigh wave phase velocity and ellipticity (the radial‐to‐vertical amplitude ratio), which provides complementary constraints to the shallow structure. Our results show a clear correlation between velocity variations in the deep crust and basin structures at the surface. We infer that the extrusion of mechanically weak mid‐to‐lower crust of Qilian is obstructed by the strong Alxa block, leading to the steep topography and deep foreland Hexi Basin. To the east, in contrast, the outward extrusion of Songpan‐Ganzi is absorbed in a wide range by the relatively weak Longzhong region, developing gently sloping topography and small intermontane basins. Furthermore, the significant structural differences of rift basins from north to south around the western Ordos likely result from tectonic regime transformation induced by the continuous expansion of NE Tibet since the late Miocene. Our results improve the understanding of how deep crustal geodynamic processes influence surface uplift and basin developments in the expanding NE Tibet. Key Points A high‐resolution 3‐D crustal model of NE Tibet is obtained by joint inversion of Rayleigh wave ellipticity and phase dispersion We infer that deep crust extrusion and strength differences across plateau boundaries control distinct surface deformation in NE Tibet The systematic thinning of basins in west Ordos indicates tectonic regime transformation due to expansion of Tibet since Miocene

It is well known that for the local isotropic elastic half-spaces, there always exists a unique Rayleigh wave. However, as shown in this paper, for the nonlocal isotropic elastic half-spaces, the existence picture of Rayleigh waves is more complicated. It contains the domains (of the material and nonlocality parameter) for which only one Rayleigh wave can propagate, the domains that support exactly two Rayleigh waves and the domains where three Rayleigh waves are possible. When two or three Rayleigh waves exist, one wave is the counterpart of the local (classical) Rayleigh wave, the other waves are new Rayleigh modes. Remarkably, the new modes can travel with high velocity at small wave numbers. The existence results are proved by employing the complex function method. The formulas for the wave velocity of Rayleigh waves have also been derived and they will be useful in various practical applications.

Purpose This paper addresses a significant research gap in the study of Rayleigh surface wave propagation within a piezoelectric medium characterized by piezoelectric properties, thermal effects and voids. Previous research has often overlooked the crucial aspects related to voids. This study aims to provide analytical solutions for Rayleigh waves propagating through a medium consisting of a nonlocal piezo-thermo-elastic material with voids under the Moore–Gibson–Thompson thermo-elasticity theory with memory dependencies. Design/methodology/approach The analytical solutions are derived using a wave-mode method, and roots are computed from the characteristic equation using the Durand–Kerner method. These roots are then filtered based on the decay condition of surface waves. The analysis pertains to a medium subjected to stress-free and isothermal boundary conditions. Findings Computational simulations are performed to determine the attenuation coefficient and phase velocity of Rayleigh waves. This investigation goes beyond mere calculations and examines particle motion to gain deeper insights into Rayleigh wave propagation. Furthermore, this investigates how kernel function and nonlocal parameters influence these wave phenomena. Research limitations/implications The results of this study reveal several unique cases that significantly contribute to the understanding of Rayleigh wave propagation within this intricate material system, particularly in the presence of voids. Practical implications This investigation provides valuable insights into the synergistic dynamics among piezoelectric constituents, void structures and Rayleigh wave propagation, enabling advancements in sensor technology, augmented energy harvesting methodologies and pioneering seismic monitoring approaches. Originality/value This study formulates a novel governing equation for a nonlocal piezo-thermo-elastic medium with voids, highlighting the significance of Rayleigh waves and investigating the impact of memory.

The 15 January 2022, eruption at Hunga Tonga‐Hunga Ha'apai (HTHH) volcano started shortly after 4:00UTC. There had been noted unconfirmed precursory events. We analyzed seismometer data recorded in Fiji and Futuna, the closest stations operated during the eruption and located over 750 km away. We extracted Rayleigh waves and estimated their powers and source directions, assuming retrograde particle motions. We found a Rayleigh wave from the HTHH's direction about 15 min before the eruption onset. The arrival time difference of the Rayleigh wave between the two stations was consistent with that of the M5.8 earthquake during the eruption located beneath the HTHH. Referring to other seismic signals and satellite images, we concluded that the Rayleigh wave was the most significant eruption precursor with no apparent surface activity. Including our findings and results of previous studies, we propose a scenario of the beginning of the caldera‐forming eruption. Plain Language Summary Hunga Tonga‐Hunga Ha'apai (HTHH) volcano in Tonga had a caldera‐forming eruption on 15 January 2022. Disturbances associated with the eruption were recorded worldwide and by satellites. Many studies analyzed the data and reported that the eruption onset was shortly after 04:00UTC on January 15. However, some articles reported unconfirmed waves about 15 min before the eruption onset. This study is motivated by the following questions: (a) Were the unconfirmed waves actual? (b) Were they related to the eruption? (c) How did the huge eruption start? (d) How can we improve the monitoring of remote‐island and submarine volcanoes? Here, we analyzed data recorded at the closest seismic stations over 750 km away. We confirmed that a precursor event occurred ∼${\\sim} $ 15 min before the eruption and generated a significant seismic wave. This event might have been the trigger of the eruption. This study demonstrated that distant seismic stations and appropriate analysis methods will allow us to capture precursors leading to a catastrophic eruption. Key Points The volcano generated Rayleigh waves about 15 min before the giant eruption with no apparent surface activity These waves dominated in 0.03–0.1 Hz with amplitudes comparable to the amplitude of M4.9 Seismic stations 750 km from the volcano and appropriate data analyses allowed us to capture precursors of the catastrophic eruption

Rayleigh wave ellipticity measurements from seismic ambient noise recorded on the Greenland Ice Sheet (GrIS) show complex and anomalous behavior at wave periods sensitive to ice (T < 3–4 s). To understand these complex observations, we compare them with synthetic ellipticity measurements obtained from synthetic ambient noise computed for various seismic velocity and attenuation models, including surface wave overtone effects. We find that in dry snow conditions within the interior of the GrIS, to first order the anomalous ellipticity observations can be explained by ice models associated with the accumulation and densification of snow into firn. We also show that the distribution of ellipticity measurements is strongly sensitive to seismic attenuation and the thermal structure of the ice. Our results suggest that Rayleigh wave ellipticity is well suited for monitoring changes in firn properties and thermal composition of the Greenland and Antarctic ice sheets in a changing climate. Plain Language Summary Surface meltwater is increasingly being routed and distributed through the Greenland Ice Sheet (GrIS) changing the mechanical and thermal properties of the ice and resulting in accelerated ice flow. Here we observe complex and anomalous Rayleigh wave ellipticity measurements at periods sensitive to the ice structure. We compare our observations with ellipticity measurements made on simulated seismic noise for various seismic velocity and attenuation models. We demonstrate that in the interior of the GrIS the ellipticity is sensitive to the accumulation and densification of snow as it compacts into glacier ice. The variation in the measurements is strongly sensitive to the thermal structure of the ice sheet which we estimate to be warmer than about −10°. These results demonstrate that Rayleigh wave ellipticity is well suited for monitoring changes in firn properties and thermal composition of the Greenland and Antarctic ice sheets in a changing climate. Key Points Densification of snow into firn has a first order effect on ellipticity measurements at periods sensitive to the ice The distribution of ellipticity measurements is sensitive to the thermal composition of the ice Ellipticity is a promising method for long term monitoring of ice properties and thickness beneath the seismic station