Earthquake Research Advances最新文献

The seismic performance of medical systems is crucial for the seismic resilience of communities. The report summarizes the observed damage to twelve hospital buildings in the area affected by the M_W 7.8 and M_W 7.5 earthquakes on February 6, 2023 in Turkey. They include five base-isolated buildings and seven fixed-base buildings in southcentral Turkey's seven most heavily affected provinces. By relating the post-quake occupancy statuses of the hospitals with the estimated seismic demands during the earthquake doublet, the report offers the following observations: (1) the base-isolated hospital buildings on friction pendulum bearings generally exhibited superior performance of achieving the goal of immediate occupancy and provided better protection for nonstructural elements than fixed-base counterparts did; (2) the fixed-base hospital buildings of reinforced concrete structures constructed after 2001 successfully achieved the goal of collapse prevention even under very high seismic demands; (3) some fixed-base hospitals also remained operational even if they were very close to the fault rupture and were subjected to higher-than-design-level earthquake ground motions.

Based on the seismic data recorded by the China Earthquake Networks Center (CENC) in the Luxian area from January 2009 to October 2021, the 3D V_P, V_S, V_P/V_S structures and seismic locations of the area are obtained by joint inversion using the V_P/V_S model consistency-constrained double-difference tomography method (tomoDDMC). The earthquakes in the study area are mainly concentrated at a depth of 2–6 ​km, and the focal depth is generally shallow. The M_S 6.0 Luxian earthquake occurred at the transition zone of high- and low-velocity anomalies and the aftershock sequence was distributed along the edge of the low-V_P zone. A small number of foreshocks occurred on the west side of the M_S 6.0 Luxian earthquake, while most of the aftershocks were distributed on the east side of the M_S 6.0 Luxian earthquake. The aftershock sequence consisted of three seismic bands with different trends, and the overall distribution was in a NWW direction, which was inconsistent with the spatial distribution of the main active faults nearby. In addition, the spatiotemporal distribution of earthquakes and the variation of b-values are closely related to the industrial water injection activities in the study area, reflecting the activation of pre-existing hidden faults under certain tectonic and stress environments leading to seismic activities in the area.

To reveal the seismogenic mechanism of the Luding earthquake, we employed the 118 China Seismic Network stations to collect the P-wave polarity data from each station, which was then used in the P-wave first motion approach to calculate the focal mechanism solution of the M6.8 Luding earthquake that occurred on September 5, 2022. We have also studied the loading effect of tectonic stress on the Luding earthquake fault based on the stress field data for the research area. The results indicate that this earthquake was a strike-slip type, the nodal plane I: strike 167°, dip Angle 78°, slip Angle 2°; Nodal plane Ⅱ: strike 77°, dip Angle 88°, slip Angle 168°. The two fault planes’ instability coefficients of the Luding earthquake are examined considering the region’s background stress field’s condition. The nodal plane I in the Moho circle is discovered to practically coincide with the Coulomb failure line and the tangent point of the Moho circle, indicating that this nodal plane has a high instability coefficient compared to the nodal plane II. The conclusion is that the nodal plane I has a higher likelihood of being the seismogenic fault plane, which is congruent with the seismogenic fault plane suggested by the aftershock distribution, the earthquake radiation energy distribution of a single station, and seismic intensity distribution. The Luding earthquake’s focal mechanism is highly like the theoretical focal mechanism of the fault situated at the location where the Coulomb failure line intersects the Mohr circle, demonstrating that background stress is what caused the earthquake. The substantial fault instability and similarity between the solved and theoretical focal mechanisms make it easier to comprehend the loading effect of tectonic stress on the Luding earthquake fault.

The relationship of the crustal contact between the Indian and Eurasian plates is a key issue in understanding crustal thickening and the subduction of the Indian lithosphere beneath the Qinghai-Tibetan Plateau. Across the middle of the Yarlung-Zangbo Suture (YZS), we deployed an ∼450-km-long SN-trending wide-angle reflection/refraction profile to observe the P-wave velocity (v_P) structure beneath the northern Himalaya and the southern plateau. Our results show that, 1. the high v_P (∼7.1 ​km/s) indicates that the Indian lower crust extends no more than 50 ​km north of the YZS. 2. The lower crust beneath the southern part of the plateau features an extremely low v_P (<6.7 ​± ​0.2 ​km/s). 3. Compared with the velocities of several typical crustal lithologies in different temperature regimes, the low v_P in the lower crust can be explained by felsic-intermediate granulite, which has prevented the lower crust from further eclogitization. We propose that the dip angle of the Indian lithospheric slab beneath the YZS is partly controlled by the composition of the lower crust of the plateau. In the northern middle YZS, the crust of the southern plateau is too thick and blocks the northward advancement of the Indian lower crust, resulting in the subduction of the Indian lithospheric slab into the upper mantle. The lower crust in western and eastern Lhasa is dominated by a mafic composition, and it was delaminated after eclogitization before the Miocene. The void zone generated by delamination favors the flattening and underthrusting of the Indian lower crust.

Laboratory experiments and numerical simulations on rock friction perturbations, an important means for understanding the mechanism and influencing factors of stress-triggered earthquakes, are of great significance for studying earthquake mechanisms and earthquake hazard analysis. We reviews the experiments and numerical simulations on the effects of stress perturbations on fault slip, and the results show that stress perturbations can change fault stress and trigger earthquakes. The Coulomb failure criterion can shed light on some questions about stress-triggering earthquakes but cannot explain the time dependence of earthquake triggering nor be used to investigate the effect of heterogeneous stress perturbations. The amplitude and period are important factors affecting the correlation between stress perturbation and fault instability. The effect of the perturbation period on fault instability is still controversial, and the effect of the high-frequency perturbation on earthquakes may be underestimated. Normal and shear stress perturbation can trigger fault instability, but their effects on fault slip differ. It is necessary to distinguish whether the stress perturbation is dominated by shear or normal stress change when it triggers fault instability. Fault tectonic stress plays a decisive effect on the mode of fault instability and earthquake magnitude. Acoustic emission activity can reflect the changes in fault stress and the progression of fault nucleation, and identify the meta-instability stage and precursor of fault instability, providing a reference for earthquake prediction.

In this study, we used high-resolution optical satellite images on the Google Earth platform to map large-scale landslides in Xianyang City, Shaanxi Province, China. After mapping, a comprehensive and detailed large-scale landslide inventory that contains 2924 large-scale landslides was obtained. We analyzed the spatial distribution of landslides with seven influencing factors, including elevation, slope angle, aspect, curvature, lithology, distance to a river, and distance to the fault. Landslide Number, Landslide Area, Landslide Number Density (LND), and Landslide Area Percentage (LAP) were selected as indexes for the spatial distribution analysis. The results show that the number and area of landslides in the elevation range of 1000–1200 ​m is the highest. The highest number of landslides was observed in the slope angle of 25°–30°. North-facing slopes are prone to sliding. The area and number of landslides are the largest when the slope curvature ranges from −1.28 to 0. The LND and LAP reach their maxima when the slope curvature is less than −2.56. Areas covered by the Tertiary stratum with weakened fine-grained sandstone and siltstone show the highest LND and LAP values. Regarding distance to a river, the LAP peaks in the range of 300–600 ​m, whereas the LND peaks in an area larger than 2100 ​m. The values of LND and LNP rise as the distance from the faults increases, except for the locations 30 ​km away from active faults. This phenomenon is because active faults in this area pass through the plain areas, while landslides mostly occur in mountainous areas. The cataloging of landslide development in Xianyang City provides a significant scientific foundation for future research on landslides. In addition, the spatial distribution results are useful for landslide hazard prevention decisions and provide valuable references in this area.

The Anninghe fault is a major left-lateral strike-slip fault in southwest China and a seismic gap with a potential earthquake larger than M_W 7.0 lies in the Mianning-Xichang segment according to recent observations. The shallow structure of this region can offer a glimpse into the geometry of the fault, which plays an important role in earthquake hazard mitigation. To further investigate the sedimentary structure of the Anninghe fault zone, two dense linear arrays with a station spacing of around 80 ​m were deployed across the fault. In this study, the H/V spectral ratio (HVSR), together with its peak frequency at each station site, was obtained by applying the Nakamura method. Our findings demonstrate that the peak frequency behaves in high correlation with lithology and is controlled by topography. HVSR in foothills or regions with magmatic intrusion shows a single peak at about 2–3 ​Hz. In locations with abundant Quaternary sedimentation, such as Anninghe valleys and fracture zones, another low-frequency peak around 0.4 ​Hz can be noticed in HVSR. By using the empirical relationship, the thickness of the sedimentary layer around the fault fracture zone is estimated to be 300–600 ​m. Furthermore, the sedimentary interface shows a downward dip to the east, possibly influenced by the east-west extrusion stress. Considering the resonance effect, buildings with 6–9 stories in the valley area of the Anninghe require additional attention in earthquake hazard prevention.

The Litang fault (LTF), located in the southeast of the Qinghai-Tibetan Plateau, is known for its high level of present-day seismicity, whereas its Pleistocene activity has been scarcely documented. This study focused on a tract of banded travertine deposits precipitated from thermal waters along the NW–SE-trending LTF trace. The role of travertine deposits in recording neotectonic activity has been studied by identifying their internal structure. Typical soft-sediment deformation structures observed within the banded travertines include micro folds, liquefied breccia, and liquefied diapirs. These deformed structures, which are restricted to a single unit separated unconformably by undeformed layers, can be traced for tens of meters, indicating that they were formed by seismic shaking triggered by LTF activity. The deformation of the banded travertine layers is attributed to the combined effects of seismic shaking, liquefaction, and fluidization, and it can be related to a paleo earthquake event with a magnitude of M_S ​> ​5. The U-series ages obtained from the banded travertine deposits perturbed by the earthquakes are in the range of 130.59–112.94 ka, indicating an important fault-assisted neotectonic activity that occurred during the Middle–Late Pleistocene. Analysis of such structures, in combination with the use of U-series dating methods, can yield a reliable timing of neotectonic activity and provide new evidence for understanding the seismotectonic setting of the Litang area.

The Antarctic ice sheet is an important target of Antarctic research. Thickness and structure, including intraice and subice, are closely related to the mass balance of the ice sheet, and play an important role in the study of global sea level and climate change. Subglacial topography is an important basis for studying ice sheet dynamics and ice sheet evolution. This paper briefly reviews the geophysical detection methods and research status of the Antarctic ice sheet: (1) Conventional methods such as ice radar are the main methods for studying the ice sheet today, and passive source seismic methods such as the receiver function method, H/V method and P-wave coda autocorrelation method have good development prospects; (2) the high-resolution (1 ​km) ice thickness and subglacial topographic database BEDMAP2 established based on various data has greatly improved the ability to detect internal isochronous layers, anisotropic layers, and temperature changes within ice and has advanced research on ice sheet evolution; and (3) ice radar, numerical simulation and core drilling are the main methods to study subglacial lakes and sediments. More than 400 subglacial lakes have been confirmed, and more than 12 000 simulation results have been obtained. Research on the Antarctic ice sheet faces enormous challenges and is of great urgency. Aiming at hot issues, such as Antarctic geological evolution, glacial retreat, ice sheet melting and their relationships with global climate change, it is the frontier and trend of future Antarctic ice sheet research to carry out multidisciplinary and multicountry comprehensive geophysical exploration based on the traditional ice radar method combined with passive seismic methods, especially new technologies such as short-period dense array technology, unmanned aerial vehicles and artificial intelligence. This is expected to further promote Antarctic research.