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Earthquake Science 2010年第2期23卷 149-155页

作者： zengxi ge Department of geophysics School of Earth and Space Sciences Peking University Beijing 100871 China

We presented a boundary element method using the approximate analytical Green＇s function given by Sanchez-Sesma et al. Coordinate transform is introduced to extend the method to deal with the model with constant-gradient velocity along oblique direction. The method is validated by comparing the numerical results with other independent methods. This method provides a useful tool for analyzing local site effects. We computed seismic response for two series of models. The results in both frequency and time domains are analyzed and show complex amplification patterns. The fundamental mode of resonance is dependent not only on the velocity at the free surface but also on the velocity distribution of the whole basin. For the higher modes of vibration the heterogeneous basin also has its own characteristic.

关键词： boundary element SH wave seismic response constant-gradient velocity

Resolving rupture processes of great earthquakes: Reviews and perspective from fast response to joint inversion

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Science China Earth Sciences 2020年第4期63卷 492-511页

作者： Han YUE Yong ZHANG zengxi ge Teng WANG Li ZHAO School of Earth and Space Sciences Peking UniversityBeijing 200871China

Resolving rupture processes of great earthquakes has fundamental importance to the study of earthquake physics,rupture dynamics, fault zone structure, and evolving processes. It also plays an essential role in earthquake hazard estimation,emergency response and seismic hazard mitigation. This paper reviews the major progress of the earthquake rupture process studies in the last decades, with an emphasize on the research directions of the department geophysics of Peking University including real-time response, back-projection techniques, geodetic data analysis, joint inversion and inversion in complex earth medium. We discussed the advantages and limitations of tradition methods;proposed a systematic and integrated approach from fast-response to detailed study. We also raised perspectives of using source models for ground motion prediction and the possibility of full-dynamic inversion.

关键词： Finite fault model Backprojection Joint inversion Strong motion Simulation

Long-term seismic network in South China Sea by floating MERMAIDs

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Science China Earth Sciences 2023年第9期66卷 1979-1993页

作者： Yong YU Yongshun John CHEN Zhen GUO zengxi ge Department of Ocean Science and Engineering Southern University of Science and TechnologyShenzhen 518055China Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou) Guangzhou 511458China School of Earth and Space Science Peking UniversityBeijing 100871China

Seismic data coverage in ocean regions is sparse,and it is highly challenging to build long-term continuous seismic networks in the oceans due to the restrictions related to the shortage of instruments and great *** lack of data coverage limits effective seismic imaging of deep mantle structures beneath the oceans,which cover 70%of the Earth’s *** newly developed Mobile Earthquake Recorder in Marine Areas by Independent Drivers(MERMAID)can drift with ocean currents at a specified depth while recording seismic *** Southern University of Science and Technology(SUSTech)launched 10 MERMAIDs in the South China Sea(SCS)in May 2021 that formed the South China Sea Floating Seismic Network(SCS-FSN).We analyzed the one-year-long records of the SCS-FSN,identifying 372 cataloged earthquakes and acquiring 1,015 high-quality travel time *** analyzing the records of earthquakes with magnitudes above 7.0 and conducting synthetic waveform calculation,we found that,in addition to the epicentral distance and earthquake magnitude,the earthquake identification ability of the network is also affected by the focal mechanism,sea condition,seafloor relief,and MERMAID working *** the recognition rate of the SCS-FSN is only 16%for earthquakes with magnitudes above 5.5 and epicentral distances less than 90°,this network is expected to collect more than 5,000 high-quality travel time data during its five-year battery *** new data will significantly improve the seismic data coverage,compensating for the lack of long-term continuous seismic network observations in the *** importantly,with this experiment,we are confident that setting up well-designed floating seismic networks in the world’s three oceans could solve the world-class problem of the lack of effective seismic data coverage beneath ocean regions.

关键词： South China Sea MERMAID Floating seismic network Earthquake identification Seismic data coverage

Cascading multi-segment rupture process of the 2023 Turkish earthquake doublet on a complex fault system revealed by teleseismic P wave back projection method

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Earthquake Science 2024年第2期37卷 158-173页

作者： Bonan Cao zengxi ge Department of geophysics School of Earth and Space SciencesPeking UniversityBeijing 100871China Hebei Hongshan National geophysical Observatory for Thick Sediments and Seismic Hazards Peking UniversityBeijing 100871China

In this study,the vertical components of broadband teleseismic P wave data recorded by China Earthquake Network are used to image the rupture processes of the February 6th,2023 Turkish earthquake doublet via back projection *** in two frequency bands(0.5-2 Hz and 1-3 Hz)are used in the imaging *** results show that the rupture of the first event extends about 200 km to the northeast and about 150 km to the southwest,lasting~90 s in *** southwestern rupture is triggered by the northeastern rupture,demonstrating a sequential bidirectional unilateral rupture *** rupture of the second event extends approximately 80 km in both northeast and west directions,lasting~35 s in total and demonstrates a typical bilateral rupture *** cascading ruptures on both sides also reflect the occurrence of selective rupture behaviors on bifurcated *** addition,we observe super-shear ruptures on certain fault sections with relatively straight fault structures and sparse aftershocks.

关键词： 2023 Turkish earthquake doublet back projection method cascading segmented rupture process coseismic triggering super-shear ruptures

Rupture pattern of the Oct 23,2011 Van-Merkez,Eastern Turkey earthquake

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Earthquake Science 2014年第3期27卷 257-264页

作者： Hao Zhang zengxi ge Department of geophysics School of Earth and Space SciencesPeking University Department of Earth and Planetary Sciences Northwestern University2145 Sheridan RdEvanstonIL 60208USA

High-frequency rupture process of the Oct 23, 2011 Van-Merkez earthquake is imaged by back-projection method using high-quality teleseismic P wave data from the US Array, and prestack Kirchhoff migration using P wave data from a subarray of global seismic networks. The rupture model with two asperities is confirmed by previous two methods. In low-frequency imaging, a large asperity derived from the migration method corresponds to the second one from the high-frequency P waves. The con- sistency of the locations of asperities from datasets with different frequency bands indicates that there is possible insignificance of the frequency-dependent feature for the earthquake. The resultant images illustrate the spatial and temporal evolution of the rupture, which mainly propa- gated WSW over a length of 33 km during the first 18 s, accompanying with bursts of two asperities at 3 and 11-13 s. The rupture direction is confirmed by the S wave comer frequency variations of strong ground accelerations. The rupture fronts are mainly located at the updip of the causative fault. Based on polarities of the P waveforms and focal mechanisms of the mainshock and aftershocks, the failure of these two asperities is determined to have occurred on a reverse fault with a dip angle of 47°. Hence, the rupture pattern of the 2011 Van-Merkez earthquakewas dominated by a unilateral rupture toward the west- southwest direction.

关键词： 2011 Van-Merkez earthquake· Rupturepattern Back-projection Kirchhoff migration

Elastic one-return boundary element method and hybrid elastic thin-slab propagator for strong-contrast media with sharp boundaries

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Earthquake Science 2018年第2期31卷 92-99页

作者： zengxi ge Yi Luo Yuyan Ma Rushan Wu School of Earth and Space Sciences Peking University IGPP University of California

In this paper, we developed the theory and algorithm of an elastic one-way boundary element method（BEM） and a corresponding hybrid elastic thin-slab propagator for earth media with sharp boundaries between strong contrast media. This approach can takes the advantage of accurate boundary condition of BEM and completely overcomes the weak contrast limitation of the perturbationtheory based one-way operator approach. The one-way BEM is a smooth boundary approximation, which avoids huge matrix operations in exact full BEM. In addition, the one-way BEM can model the primary-only transmitted and reflected waves and therefore is a valuable tool in elastic imaging and inversion. Through numerical tests for some simple models,we proved the validity and efficiency of the proposed method.

关键词： boundary element method thin slab one-way wave propagator

利用走时和波形拟合迭代反演阿拉善地壳速度结构及2015年阿拉善左旗5.8级地震震源机制

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地球物理学报 2018年第4期61卷 1225-1237页

作者：宋超盖增喜北京大学地球与空间科学学院地球物理系北京100871

据中国地震台网测定,北京时间2015年4月15日15时39分,在内蒙古自治区阿拉善左旗(39.8°N,106.3°E)发生MS5.8地震,震源深度为10km.地震发生后多家机构对其开展了研究,本文使用喜马拉雅Ⅱ期布设在南北地震带北段的台站观测数据,通过走时... 详细信息

据中国地震台网测定,北京时间2015年4月15日15时39分,在内蒙古自治区阿拉善左旗(39.8°N,106.3°E)发生MS5.8地震,震源深度为10km.地震发生后多家机构对其开展了研究,本文使用喜马拉雅Ⅱ期布设在南北地震带北段的台站观测数据,通过走时反演和波形拟合反演的迭代,获得了该地区地壳一维速度结构,接着利用直达P波观测与理论走时差对震中位置重定位,然后反演地震的最佳双力偶解以及震源深度,最终得到了区域速度结构、地震的三维坐标、发震时刻以及震源机制解.结果显示,此次地震发生于世界时2015年4月15日7时39分26.718s,震中(39.7663°N,106.4304°E),震源矩心深度18km,矩震级MW5.25,节面Ⅰ走向176°,倾角85°,滑动角-180°,节面Ⅱ走向86°,倾角90°,滑动角-5°.结合该区域断裂带构造运动分析,本文认为此次地震是左旋走滑破裂,略带正断分量,断层面是节面Ⅱ,走向为NEE(近E-W)向,发震构造为震中附近的E-W向隐伏断裂.

关键词：阿拉善地震相位加权叠加走时反演速度结构波形拟合震源机制

Lg波Q值随震源深度的变化作为地壳本征衰减深度的判据

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地球物理学报 2019年第3期62卷 898-911页

作者：罗毅盖增喜北京大学地球与空间科学学院北京100871

Lg波的Q_(Lg)值是描述区域地壳结构及介质衰减特性的重要参数之一,Q_(Lg)层析成像被广泛应用于地壳衰减结构横向不均匀性的研究中.但是,对Q_(Lg)在垂直方向上的不均匀性的研究较少.当发现一个地区发生Q_(Lg)值低时,我们希望进一步了解... 详细信息

Lg波的Q_(Lg)值是描述区域地壳结构及介质衰减特性的重要参数之一,Q_(Lg)层析成像被广泛应用于地壳衰减结构横向不均匀性的研究中.但是,对Q_(Lg)在垂直方向上的不均匀性的研究较少.当发现一个地区发生Q_(Lg)值低时,我们希望进一步了解这种介质衰减深度.本文通过数值模拟合成地震图的方法,通过分析不同震源深度和介质模型计算Q_(Lg),判断Lg波发生主要衰减的深度.研究结果显示:(1)当震源深度浅时,上地壳介质衰减对于Lg波Q值的影响明显比下地壳的影响更大.而震源深度深时,两者贡献基本相当;(2)如果上地壳介质衰减强,则随着震源深度的增加,η值逐渐减小;如果下地壳介质衰减强,η值先增大后减小;但如果下地壳存在低速层,则η值持续增大;(3)如果上地壳介质衰减强,则随着震源深度的增加,Q_0逐渐增大;反之如果下地壳介质衰减强,则Q_0逐渐减小.因此,我们可以通过调查某一区域不同深度地震的Lg波衰减规律,来判断这一地区的地壳介质衰减情况.

关键词： Lg波衰减品质因子Q值合成地震图

2.5D boundary element simulation of wave propagation in a vertical fluid-filled borehole with irregular shape

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Applied geophysics 2007年第3期4卷 155-163页

作者： ge zengxi Wang Canyun Lei Ting Chen Xiaofei Departrnent of geophysics School-of Space and Sciences Peking University Beijing 100871 Schlumberger-Doll Research Schlumberger Beijing geoScience Center Schlumberger Beijing 100871 China

In this paper, a boundary element formulation in the wave-number space domain for solving the wave equation for a borehole with arbitrary shape in acoustic logging problems is presented. The problem is treated as a two-dimensional medium with the discrete wave- number method in the vertical direction. The method is validated by comparing the results obtained by this method with those obtained by the finite-difference method. The method is used to study the effect on wave propagation in a vertical borehole of a vertical fracture. For a monopole source, the dispersion curves for Stoneley waves yield three branches. For dipole and quadrupole sources, different orientations of the source yield different results. When the dipole source is orthogonal to the fracture, the dispersion curve is similar to that of the open hole, while the curves are quite different when the source is parallel to the fracture. These characteristics enable us to determine the orientation of the vertical fracture.

关键词： Boundary element borehole logging dispersion curves vertical fracture.

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全球大地震破裂空间复杂度特征研究

北京大学学报（自然科学版） 2022年第4期58卷 635-643页

作者：王静盖增喜北京大学地球与空间科学学院北京100871 河北红山地球物理国家野外科学观测研究站邢台054000

基于有限断层反演得到的滑移数据,用独立滑移单元的数量表征地震破裂复杂度,据此对大地震破裂进行分组,并研究破裂复杂度与主要震源参数之间的关系,探讨破裂复杂度的全球及区域空间分布特征。结果表明,矩震级很大(Mw≥8.5)的事件,地震... 详细信息

基于有限断层反演得到的滑移数据,用独立滑移单元的数量表征地震破裂复杂度,据此对大地震破裂进行分组,并研究破裂复杂度与主要震源参数之间的关系,探讨破裂复杂度的全球及区域空间分布特征。结果表明,矩震级很大(Mw≥8.5)的事件,地震破裂复杂度更大;破裂复杂度较高的地震分布在浅层地壳(≤30km)内的概率最大,随着震源深度增加,破裂复杂度对震源深度的敏感性逐渐消失;走滑断层机制占比较大的事件,破裂复杂度较高;破裂复杂度与地震能矩比没有明确的关系;破裂复杂度的空间分布特征与区域地质构造环境相关。破裂复杂度的空间分布特征可以分为3类,第一类是板块之间简单碰撞产生的俯冲带,板块交界处的滑动速率和方向较为一致,这种情形下以比较简单的事件类型为主;第二类是多板块交界处,或者板块交界处的滑动速率和方向在整个区域内存在差异;第三类是大陆内部的强烈挤压地带。与第一类空间分布特征相比,第二类和第三类情形下破裂复杂度相对更高。地震破裂复杂度可以在一定程度上反映区域应力场的复杂性。

关键词：破裂复杂度震源参数空间分布断层构造背景