On August 8th 2017,a MW6.5 earthquake struck Sichuan Province,China,resulting in significant loss of life and extensive property damage.The absence of significant surface rupture from field investigations made it challenging to identify the fault geometry and estimate the rupture evolution of this event.We applied a newly potency density tensor inversion which introduced the standard deviation of the smoothness constraints for five basis double-couple components by the weight of its each amplitude respectively to estimate the rupture pro-cess of this event.The slip distribution shows that large slip regions coincide with distribution of aftershocks,espe-cially for the depth change in the southeast and northwest epicentre.Both aftershock and slip distribution show deeper depth in northwestern segment than that southeastern segment.The spatial distribution of potency density tensors showed different total focal mechanisms for the northwest and southeast area of the epicentre,indicating that the complex seismogenic fault of the main shock may be divided into two main segments and a secondary seg-ment.The rupture process shows that the initial rupture occurred around the hypocentre in the first 2 s.Main rup-ture propagates to the up-dip part of the hypocentre while partial rupture propagates to down-dip part of the hypo-centre within the southeastern segment of the seismogenic fault during 2-6 s.Then rupture jumps to the northwest-ern area of the hypocentre and propagates with in northwest segment during 6-10 s.In addition,moderate slip ap-pears in the southeast edge of the fault plane from 5 s.High and low-velocity anomalies were identified around the hypocentre and in the northwestern and deeper parts of the hypocentre,respectively.We interpret that the brittle failure of rocks,caused by stress accumulation from middle-to-lower crustal flow and upwelling asthenosphere,may have contributed to the initiation of the 2017 Jiuzhaigou earthquake.Additionally,the deceleration and cessa-tion of the event are inferred to be related to the fault geometry along the strike direction and the seismogenic envir-onment at depth.
The X-discontinuity in the upper mantle of the Earth's interior,typically located at depths of approxi-mately 250-350 km,is critical for unraveling mantle composition and dynamics.However,its global distribution and underlying formation mechanisms remain poorly constrained.Conventional methods for identifying this dis-continuity using teleseismic P-wave receiver functions rely heavily on post-stacking empirical interpretation,which is inefficient and unsuitable for processing large volumes of seismic data.To address the challenges posed by massive datasets and the scarcity of manually labeled samples,this study proposes a transfer learning strategy termed"pretraining on synthetic data followed by fine-tuning with real data".We construct a convolutional neural network-based binary classification model to determine the presence or absence of the X-discontinuity.The proce-dure is as follows:First,synthetic receiver function datasets—with and without the X-discontinuity—are generated through forward modeling based on three classical velocity models(AK135,IASP91,and PREM).Noise augmen-tation and temporal trimming are applied to improve model generalization.Second,high-quality observed data are selected from global seismic networks and manually annotated to create a real dataset.Finally,a two-phase training approach is adopted,where the model is sequentially trained on the synthetic and real datasets to achieve auto-mated detection of the X-discontinuity.Experimental results show that the trained model achieves an accuracy of approximately 90%in classifying receiver function images.In determining the presence of the X-discontinuity be-neath seismic stations,the model exhibits about 80%agreement with results derived from conventional methods,indicating its effectiveness in automated detection.Based on this approach,subsequent research will systematically investigate the global distribution of the X-discontinuity.
On January 7,2025,an MW7.1 earthquake struck Dingri County,Xigaze City,on the southern mar-gin of the Qinghai-Xizang Plateau,China.The epicenter was located at the intersection between the southern seg-ment of the Shenzha-Dingjie Rift and the South Xizang Detachment System,a tectonically complex region charac-terized by active extensional deformation.The earthquake induced large-amplitude coseismic surface deformation with a highly heterogeneous spatial distribution.To clarify the seismogenic structural characteristics and fault slip distribution of this event,we conducted a systematic investigation by integrating Interferometric Synthetic Aper-ture Radar(InSAR)observations with seismic source mechanism and fault slip inversion methods.(1)The InSAR-derived deformation fields reveal that the coseismic deformation was dominated by a nearly north-south-trending subsidence zone,with a maximum line-of-sight(LOS)subsidence of approximately 1.4 m and a maximum uplift of about 0.9 m.The two-dimensional deformation field further indicates pronounced subsidence accompanied by westward horizontal motion on the western side of the fault,while the eastern side exhibits relative uplift and east-ward motion.These deformation characteristics suggest that the earthquake rupture was primarily governed by nor-mal faulting,with a minor strike-slip component.(2)Based on the assumption of a homogeneous elastic half-space,a single-fault model was first employed to invert the observed coseismic deformation,yielding the optimal geomet-ric parameters for the Dengmocuo Fault,with a strike of 184.6° and a dip angle of 54°.Although this single-fault model satisfactorily explains the major deformation features in the vicinity of the main fault,significant residual de-formation remains on the western side of the fault.This result indicates the inherent limitations of a single planar fault model in fully reproducing the complete spatial pattern of the observed deformation field.(3)To reasonably account for the residual deformation,a conjugate double-fault model was introduced for joint inversion.The results demonstrate that the earthquake rupture was dominated by a west-dipping main fault,accompanied by the syn-chronous rupture of an east-dipping,high-angle subsidiary fault.Both faults exhibit typical normal-faulting charac-teristics.Compared with the single-fault model,the conjugate double-fault model significantly improves the de-formation fitting accuracy,particularly within incoherent zones near the subsidiary fault,and provides a more com-prehensive explanation for the overall observed deformation pattern.Assuming a shear modulus of 30 GPa,the joint inversion based on the double-fault model yields a total seismic moment of approximately 3.69×1019 N·m,corresponding to a moment magnitude of MW7.03.The results indicate that the 2025 Dingri earthquake represents a typical conjugate normal-faulting rupture event within the southern Xizang Rift System.This study highlights the important role of conjugate fault systems in strain partitioning and energy release in extensional tectonic settings and provides valuable insights into the regional deformation mechanisms and seismic hazard assessment of the southern Qinghai-Xizang Plateau.
On January 7,2025,anMW 7.1 earthquake struck Dingri,Xizang,causing severe engineering damage in the epicentral area.To scientifically reconstruct the ground motion impact field of this event,a strong ground motion simulation model was established based on the stochastic finite-fault method,incorporating the inverted source rupture process.A systematic study on key sensitive parameters was conducted:by comparing the mean values of 30 stochastic realizations with the pseudo-acceleration spectra(PSA)recorded at early warning stations,the op-timal stress drop was determined to be 10.0 MPa;meanwhile,the high-frequency attenuation parameter(κ)was es-timated as 0.032 6 based on the negative correlation between its median value and site source,path,and site parameters,a reliability test was performed using observational data from the National Seis-mic Intensity Management and Early Warning Project.Consequently,the gridded distributions of peak ground ac-celeration(PGA)and instrumental seismic intensity were generated,and the spatial distribution characteristics and formation mechanisms of the strong ground motion field were quantitatively discussed.The results indicate that:(1)Under a 5%damping ratio,the simulated PSA values match the observations well in both amplitude and spectral shape within the period range of 0.04-4.00 s.The residuals mainly fall within the range of±1.0 without significant period dependence,verifying the reliability of the model in the complex crustal environment of the southern Qing-hai-Xizang Plateau.(2)The simulated ground motion intensity isovalues exhibit a nearly north-south elliptical dis-tribution.The peak PGA near the epicenter reaches 1 184.3 cm/s2,with a calculated instrumental seismic intensity of 9.6.While covering the actual seismic damage risk,the simulation results show good consistency with both macro-seismic investigations and instrumental observations.(3)The ground motion intensity field clearly demon-strates significant rupture directivity and hanging-wall effects.Specifically,the PGA in the forward rupture direc-tion(northward)is approximately 1.82 times that in the backward direction,and the PGA on the hanging wall is amplified by approximately 1.85 times compared to the footwall.These refined spatial distribution characteristics provide a dynamic basis for explaining macro-seismic damage variations and offer important scientific references for the seismic design of rural buildings and emergency response in southern Xizang.
High-precision theoretical modelling of gravity field variations induced by multiple known mechanisms is a prerequisite for studying dynamic processes of the Earth's surface and interior through gravimetry. Temperature fields on the Earth and other celestial bodies, driven by factors such as solar radiation and magmatic eruptions, often exhibit periodic or step-like fluctuations. These thermal perturbations not only generate deformation fields but also disturb the gravity field. In this study, we employ a thermoelastic half-space model and solve the governing partial differential equations analytically to derive explicit expressions for the deformation and gravity changes induced by surface point and disk-shaped heat sources under periodic and step-like temperature fluctuations. The results demonstrate that gravity variations at the surface caused by thermoelastic effects are manifested solely as the free-air gradient effect due to the movement of gravimetric instruments with surface deformation, while the contributions from internal strain and Bouguer-layer surface displacement cancel each other at the first order. Finally, two representative examples are presented to illustrate the magnitude of thermoelastic deformation and its gravitational effects: (1) for periodic temperature fluctuations on the lunar surface, the resulting surface uplift is estimated to be at the sub-millimeter level, with gravity changes smaller than the microgal level; (2) for a sudden temperature disturbance in the permanent Lava Lake of Mount Nyiragongo, assuming a magma lake with a radius of 400 m and a temperature increase of 40 K, the predicted stable thermoelastic vertical displacement at the center is about 10 cm and the associated gravity change is about 30 μGal.
