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An eikonal equation-based earthquake location method by inversion of multiple phase arrivals

Science China Earth Sciences 2024年第6期67卷 1802-1817页

作者： Gaoyue LAO dinghui yang Shaolin LIU Guiju DONG Wenshuai WANG Kui LIU National Institute of Natural Hazards Ministry of Emergency Management of ChinaBeijing 100085China School of Earth Sciences Yunnan UniversityKunming 650091China Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China School of Mathematics and Statistics Ningxia UniversityYinchuan 750021China

The precise determination of earthquake location is the fundamental basis in seismological community,and is crucial for analyzing seismic activity and performing seismic tomography.First arrivals are generally used to practically determine earthquake locations.However,first-arrival traveltimes are not sensitive to focal depths.Moreover,they cannot accurately constrain focal depths.To improve the accuracy,researchers have analyzed the depth phases of earthquake locations.The traveltimes of depth phases are sensitive to focal depths,and the joint inversion of depth phases and direct phases can be implemented to potentially obtain accurate earthquake locations.Generally,researchers can determine earthquake locations in layered models.Because layered models can only represent the first-order feature of subsurface structures,the advantages of joint inversion are not fully explored if layered models are used.To resolve the issue of current joint inversions,we use the traveltimes of three seismic phases to determine earthquake locations in heterogeneous models.The three seismic phases used in this study are the first P-,sPg-and PmP-waves.We calculate the traveltimes of the three seismic phases by solving an eikonal equation with an upwind difference scheme and use the traveltimes to determine earthquake locations.To verify the accuracy of the earthquake location method by the inversion of three seismic phases,we take the 2021 M_(S)6.4 yangbi,Yunnan earthquake as an example and locate this earthquake using synthetic and real seismic data.Numerical tests demonstrate that the eikonal equation-based earthquake location method,which involves the inversion of multiple phase arrivals,can effectively improve earthquake location accuracy.

关键词： Earthquake location Eikonal equation Fast marching method Heterogeneous model

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Geometry-preserving full-waveform tomography and its application in the Longmen Shan area

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Science China Earth Sciences 2022年第3期65卷 437-448页

作者： Xingpeng DONG dinghui yang Hejun ZHU Yun CHEN Institute of Geology China Earthquake AdministrationBeijing 100029China Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China Department of Geosciences The University of Texas at DallasDallas 75080USA State Key Laboratory ofLithospheric Evolution Institute of Geology and GeophysicsChinese Academy of SciencesBeijing 100029China

Classic L2-norm-based waveform tomography is often plagued by insurmountable cycle skipping problems;as a result,the iterative inversion falls into local minima,yielding erroneous images.According to the optimal transportation theory,we adopt a novel geometry-preserving misfit function based on the quadratic Wasserstein metric(W2-norm),which improves the stability and convexity of the inverse problem.Numerical experiments illustrate that W2-norm-based full-waveform tomography has a larger convergence radius and a faster convergence rate than the L2-norm and can effectively mitigate cycle skipping issues.We apply this method to the Longmen Shan area and obtain a reliable lithospheric velocity model.Our tomographic results indicate that the crystalline crust underlying the Sichuan Basin wedges into the crustal interior of the Tibetan Plateau,and the mid-lower crust of the eastern Tibetan Plateau is characterized by low shear-wave velocities,indicating that ductile crustal flow and strong interactions between terranes jointly dominate the uplift behavior of the Longmen Shan.Furthermore,we find that large earthquakes(e.g.,the Wenchuan and Lushan events)occur not only at the junction between high-and low-velocity regions but also in the transition zone from positive to negative radial anisotropy.These findings improve our understanding of the mechanism responsible for large earthquakes in this region.

关键词： Optimal transportation Geometry-preserving properties Cycle skipping problem Longmen Shan Lower crustal flow model

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THE WASSERSTEIN-FISHER-RAO METRIC FOR WAVEFORM BASED EARTHQUAKE LOCATION

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Journal of Computational Mathematics 2023年第3期41卷 437-457页

作者： Datong Zhou Jing Chen Hao Wu dinghui yang Lingyun Qiu Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China Yau Mathematical Sciences Center Tsinghua UniversityBeijing 100084China Yanqi Lake Beijing Institute of Mathematical Sciences and Applications Beijing 101408China

In this paper,we apply the Wasserstein-Fisher-Rao(WFR)metric from the unbalanced optimal transport theory to the earthquake location problem.Compared with the quadratic Wasserstein(W2)metric from the classical optimal transport theory,the advantage of this method is that it retains the important amplitude information as a new constraint,which avoids the problem of the degeneration of the optimization objective function near the real earthquake hypocenter and origin time.As a result,the deviation of the global minimum of the optimization objective function based on the WFR metric from the true solution can be much smaller than the results based on the W2 metric when there exists strong data noise.Thus,we develop an accurate earthquake location method under strong data noise.Many numerical experiments verify our conclusions.

关键词： The Wasserstein-Fisher-Rao metric The quadratic Wasserstein metric Inverse theory Waveform inversion Earthquake location

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Velocity structure and radial anisotropy beneath the northeastern Tibetan Plateau revealed by eikonal equation-based teleseismic P-wave traveltime tomography

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Science China Earth Sciences 2022年第5期65卷 824-844页

作者： Mengyang LI Shaolin LIU dinghui yang Xiwei XU Wenhao SHEN Chaodi XIE Wenshuai WANG Shuxin yang National Institute of Natural Hazards Ministry of Emergency Management of ChinaBeijing 100085China School of Earth Sciences Yunnan UniversityKunming 650091China Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China School of Mathematics and Statistics Ningxia UniversityYinchuan 750021China

The northeastern Tibetan Plateau serves as the frontier for the northeastward expansion of the plateau.In this area,the Tibetan Plateau interacts with the surrounding blocks,such as the Alxa Block,the Ordos Block,the Kunlun-West Qinling belt and the Sichuan Basin.Because of this expansion and interaction,this area suffers from intense deformation.At present,the evolution and deformation mechanisms of the northeastern Tibetan Plateau remain controversial.To provide new insights into these mechanisms,in this study,we conduct tomography of the P-wave velocity and radial anisotropy structures beneath the northeastern Tibetan Plateau.We choose a total of 667 teleseismic earthquakes from August 2006 to October 2020.Waveforms of these earthquakes were recorded by 921 broadband seismic stations in the northeastern Tibetan Plateau and surrounding areas.We first perform cross-correlation on waveforms of each station pair and obtain 770,749 P-wave traveltime differences.Then,we invert the differential traveltime data by applying eikonal equation-based teleseismic tomography.Finally,the P-wave velocity and radial anisotropy structures at depths from 30 to 800 km below the northeastern Tibetan Plateau are obtained.Our tomographic model shows clear low-velocity anomalies and positive radial anisotropy in the lower crust under the northeastern Qilian orogen,the northeastern Songpan-Ganzi belt and the western Qinling fold zone.These features are integrated to demonstrate the existence of lower crustal flow in the study area.Prominent low-velocity anomalies and positive radial anisotropy are found in the uppermost mantle beneath the Qilian orogen,the northeastern Songpan-Ganzi belt and western Qinling fold zone.These characteristics are combined to infer a weak lithosphere and horizontal asthenospheric flow under these tectonic units.Both the Ordos Block and the Sichuan Basin exhibit clear high-velocity anomalies and negative radial anisotropy in the uppermost mantle,thereby reflecting the high mechanical strength of the lithosph

关键词： Northeastern Tibetan Plateau Tomography P-wave velocity Radial anisotropy structure Indian plate

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青藏高原东北缘基于W2度量的全波形成像

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地球物理学报 2024年第3期67卷 843-854页

作者：董兴朋杨顶辉蒙伟娟中国地震局地质研究所北京100029 清华大学数学科学系北京100084

本研究收集青藏高原东北缘区域114个宽频带地震台站记录到的50个区域地震事件波形数据,采用基于二次Wasserstein(W2)度量的全波形成像方法,获得了10~100 s频带下该区域的高分辨率壳幔结构图像.结果显示,秦岭造山带中下地壳呈高速特征,... 详细信息

本研究收集青藏高原东北缘区域114个宽频带地震台站记录到的50个区域地震事件波形数据,采用基于二次Wasserstein(W2)度量的全波形成像方法,获得了10~100 s频带下该区域的高分辨率壳幔结构图像.结果显示,秦岭造山带中下地壳呈高速特征,表明高原内部弱物质未流入此处;而从松潘—甘孜地块跨过昆仑断裂至秦祁地块内的中下地壳呈现低S波速、正径向各向异性(V_(SH)>V_(SV))和高泊松比异常,暗示深部地壳物质存在水平流动.在秦祁地块中部,深部地壳高速特性及负径向各向异性(V_(SH)

关键词：青藏高原东北缘 Wasserstein度量波形反演地壳流径向各向异性泊松比

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Receiver function imaging of dense seismic array and deep dynamic mechanism beneath the eastern South China

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Science China Earth Sciences 2023年第6期66卷 1289-1308页

作者： Rubing HAN dinghui yang Qiusheng LI Rong HUANG Hongshuang ZHANG Jiangtao LI Hao CHEN Zhuo YE Wei FU Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources Institute of GeologyChinese Academy of Geological SciencesBeijing 100037China Institute of Geophysics and Geomatics China University of GeosciencesWuhan 430074China School of Geodesy and Geomatics Wuhan UniversityWuhan 430079China State Key Laboratory of Nuclear Resources and Environment East China University of TechnologyNanchang 330001China SinoProbe Center Chinese Academy of Geological SciencesBeijing 100037China College of Transportation Engineering Nanjing Tech UniversityNanjing 211816China

The Mesozoic tectonic framework of the eastern South China is mainly controlled by subduction,turning toward,and rollback of the Pacific Plate.Recent studies of receiver function imaging and ambient noise tomography have revealed the“Yshaped”thinnest crustal belt in the eastern South China under the overall extension of the lithosphere.However,the deep dynamic environment and formation mechanisms of the thin crustal belt remain debatable.Here we obtained high-resolution images of the crustal thickness and Poisson’s ratio in the eastern South China Block applying the recently proposed H-κ-c receiver function method,using data recorded by 305 dense portable broadband stations and 219 permanent stations surrounding.Additionally,we discussed the deep dynamic formation mechanism of the“Y-shaped”thinnest crustal belt coupled with two common conversion point stacked images at key locations.Results show that the average crustal thickness of the study area is 33 km(thin crust)and the average Poisson’s ratio is 0.24(low ratio).The overall crustal thinning toward the continental margin is likely because eastern South China was in a back-arc extension environment,which was induced by the rollback of the subducted plate in the Early Cretaceous.The crustal thickness of the“Y-shaped”thinnest crustal belt is<30 km,which is 3-5 km thinner than that outside the zone.The eastern branch is distributed along the trajectory of Nanchang-Ji’an-Ganzhou-Shaoguan-Guangzhou,and the western branch is around the Jianghan-Xiangzhong Basin,both of which intersect in Nanling.The eastern branch of the thin crustal zone indicates the potential location of the Pacific subduction slab breakoff,and the formation mechanism may be related to the interaction of deep-shallow processes,including the upwelling of mantle heat flow through the slab window and transtensional pre-existing faults.We developed a dynamic model that combines subduction-breakoff-rollback processes of the Paleo-Pacific Plate and accompanying deep fluid upwelling to explain the regio

关键词： Eastern South China Block Dense seismic array Receiver function “Y-shaped”thinnest crustal belt Slab breakoff

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A review of the influencing factors on teleseismic traveltime tomography

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Earthquake Science 2023年第3期36卷 228-253页

作者： yang Pan Shaolin Liu dinghui yang Wenshuai Wang Xiwei Xu Wenhao Shen Mengyang Li National Institute of Natural Hazards Ministry of Emergency Management of ChinaBeijing 100085China Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China School of Mathematics and Statistics Ningxia UniversityYinchuan 750021China School of Earth Sciences Yunnan UniversityKunming 650091China

Teleseismic traveltime tomography is an important tool for investigating the crust and mantle structure of the Earth.The imaging quality of teleseismic traveltime tomography is affected by many factors,such as mantle heterogeneities,source uncertainties and random noise.Many previous studies have investigated these factors separately.An integral study of these factors is absent.To provide some guidelines for teleseismic traveltime tomography,we discussed four main influencing factors:the method for measuring relative traveltime differences,the presence of mantle heterogeneities outside the imaging domain,station spacing and uncertainties in teleseismic event hypocenters.Four conclusions can be drawn based on our analysis.(1)Comparing two methods,i.e.,measuring the traveltime difference between two adjacent stations(M1)and subtracting the average traveltime of all stations from the traveltime of one station(M2),reveals that both M1 and M2 can well image the main structures;while M1 is able to achieve a slightly higher resolution than M2;M2 has the advantage of imaging long wavelength structures.In practical teleseismic traveltime tomography,better tomography results can be achieved by a two-step inversion method.(2)Global mantle heterogeneities can cause large traveltime residuals(up to about 0.55 s),which leads to evident imaging artifacts.(3)The tomographic accuracy and resolution of M1 decrease with increasing station spacing when measuring the relative traveltime difference between two adjacent stations.(4)The traveltime anomalies caused by the source uncertainties are generally less than 0.2 s,and the impact of source uncertainties is negligible.

关键词： teleseismic tomography influencing factors relative traveltime differences mantle heterogeneities station spacing

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Full waveform inversion based on the ensemble Kalman filter method using uniform sampling without replacement

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Science Bulletin 2019年第5期64卷 321-330页

作者： Jian Wang dinghui yang Hao Jing Hao Wu Department of Mathematical Sciences Tsinghua University

Full waveform inversion(FWI) has been increasingly more and more important in seismology to better understand the interior structure of the Earth. FWI, by taking advantage of both the traveltime and amplitude in the data, provides high-resolution model parameters of the earth which can produce images with high resolution. However, this inversion method conventionally suffers from non-uniqueness due to many local minima of the objective function and large computing costs. In this study, we propose a new FWI method in a semi-random framework by integrating the ensemble Kalman filter and uniform sampling without replacement. Numerical results demonstrate that the new method can achieve highresolution results and a wider convergence domain. Accordingly, the new method overcomes the disadvantage of conventional FWIs that depend strongly on the initial model.

关键词： Data assimilation Ensemble Kalman filter Uniform sampling without replacement Full waveform inversion

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A unified poroviscoelastic model with mesoscopic and microscopic heterogeneities

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Science Bulletin 2019年第17期64卷 1246-1254页

作者： Boya Zhang dinghui yang Yuanfeng Cheng Yunyin Zhang Department of Mathematical Sciences Tsinghua University Beijing 100084 China Shengli Geophysical Research Institute ofSINOPEC Dongying 257000 China

The wave-induced fluid flow(WIFF) is considered to be the main cause of dispersion and attenuation of seismic waves in fluid-saturated porous media. Among numerous theories, the mesoscopic and microscopic heterogeneities are considered to be the primary mechanisms causing the WIFF. Furthermore,in most rocks, the mesoscopic and microscopic heterogeneities exist simultaneously and can cause obvious transitions of the fast P-wave velocity, which means it is necessary to consider the influence of the two mechanisms on the dispersion and attenuation simultaneously. Numerous results have shown that the dispersions and attenuations caused by these two mechanisms can be approximated in terms of the Zener model. To combine the two mechanisms into a unified model, we introduce a new generalized Zener model into the Biot poroelasticity theory to obtain a new poroviscoelastic model. Comparisons between the numerical results and two groups of experimental data further confirm the validity of our new model.

关键词： Mesoscopic heterogeneity Microscopic heterogeneity Viscoelastic model Poroviscoelastic model

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A wave propagation model with the Biot and the fractional viscoelastic mechanisms

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Science China Earth Sciences 2021年第3期64卷 364-376页

作者： Jiaming yang dinghui yang Hongwei HAN Lingyun QIU Yuanfeng CHENG Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China Shengli Geophysical Research Institute of SINOPEC Dongying 257000China Yau Mathematical Sciences Center Tsinghua UniversityBeijing 100084China

Energy loss in porous media containing fluids is typically caused by a variety of dynamic mechanisms.In the Biot theory,energy loss only includes the frictional dissipation between the solid phase and the fluid phase,resulting in underestimation of the dispersion and attenuation of the waves in the low frequency range.To develop a dynamic model that can predict the high dispersion and strong attenuation of waves at the seismic band,we introduce viscoelasticity into the Biot model and use fractional derivatives to describe the viscoelastic mechanism,and finally propose a new wave propagation model.Unlike the Biot model,the proposed model includes the intrinsic dissipation of the solid frame.We investigate the effects of the fractional order parameters on the dispersion and attenuation of the P-and S-waves using several numerical experiments.Furthermore,we use several groups of experimental data from different fluid-saturated rocks to testify the validity of the new model.The results demonstrate that the new model provides more accurate predictions of high dispersion and strong attenuation of different waves in the low frequency range.

关键词： Poroviscoelasticity Wave propagation Dispersion and attenuation Fractional derivative

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