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An embedded electron current layer observed at the edge of the plasma sheet in the Earth’s magnetotail

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Earth and Planetary Physics 2025年第1期9卷 148-158页

作者： ChenChen Zhan RongSheng Wang QuanMing Lu San Lu XinMin Li Deep Space Exploration Laboratory/School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China Chinese Academy of Sciences(CAS)Center for Excellence in Comparative Planetology/CAS Key Laboratory of Geospace Environment/Anhui mengcheng national geophysical observatory University of Science and Technology of ChinaHefei 230026China Collaborative Innovation Center of Astronautical Science and Technology Harbin 150001China

The formation of an embedded electron current sheet within the magnetotail plasma sheet has been poorly *** this article,we present an electron current layer detected at the edge of the magnetotail plasma *** ions were demagnetized inside the electron current layer,but the electrons were still frozen in with the magnetic field ***,this decoupling of ions and electrons gave rise to a strong Hall electric field,which could be the reason for the formation of the embedded thin current *** magnetized electrons,the absence of the nongyrotropic electron distribution,and negligible energy dissipation in the layer indicate that magnetic reconnection had not been triggered within the embedded thin current *** highly asymmetric plasma on the two sides of the current layer and low magnetic shear across it could suppress magnetic *** observations indicate that the embedded electric current layer,probably generated by the Hall electric field,even down to electron scale,is not a sufficient condition for magnetic reconnection.

关键词： magnetotail plasma sheet magnetic reconnection

Influence of self-similar stresses on scenario earthquake construction:An example along the Tanlu Fault

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Science China Earth Sciences 2024年第5期67卷 1687-1697页

作者： Feng HU Huajian YAO Houyun YU Zeyu LU Jieyi HOU Song LUO Zhigang SHAO Xiaofei CHEN School of Earth and Space Sciences University of Science and Technology of ChinaHefei 230026China mengcheng geophysical national field scientific observatory Hefei 230026China Department of Earth and Space Science Southern University of Science and TechnologyShenzhen 518055China Institute of Earthquake Prediction China Earthquake AdministrationBeijing 100036China

As a famous deep and large fault in eastern China,the Tanlu Fault passes through Anhui,Jiangsu,and Shandong and into northeastern *** is important to improve the understanding of seismic hazard assessments in areas near *** start a scenario earthquake simulation in the M7.5 earthquake potential area of the Xinyi-Sihong segment of the Tanlu *** fault rupture length and width are constrained according to the scaling law of large intraplate earthquakes,the background normal stress is depth dependent,and the initial shear stresses are determined using trial and error by matching the earthquake *** the 120 km rupture length of the M7.5 earthquake,we compare the horizontal uniform stress model and self-similar stress perturbation *** findings reveal that the seismic source time function of the horizontal uniform stress model is similar to that of the Haskell model and that of the self-similar stress perturbation model is more similar to that of a real earthquake *** compare the dynamic rupture simulation and ground motion results under four different stress conditions and find that the shorter the characteristic length of the self-similar function is,the rougher the initial *** the M7.5earthquake with an epicenter in the vicinity of Suqian,the Xinyi-Tancheng segment,which is located in the IX-intensity zone north of the epicenter,vibrates more strongly on the northern side than on the southern side due to the influence of the lowvelocity zone and the peak slip *** response spectra analysis at stations in the study area is useful for improving the earthquake resistance capability.

关键词： Scenario earthquakes Self-similar stress Tanlu Fault Dynamic rupture Ground motion

Stepwise joint inversion of surface wave dispersion,Rayleigh wave ZH ratio,and receiver function data for 1D crustal shear wave velocity structure

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Earthquake Science 2017年第5期30卷 229-238页

作者： Ping Zhang Huajian Yao Laboratory of Seismology and Physics of Earth's Interior School of Earth and Space SciencesUniversity of Science andTechnology of ChinaHefei 230026AnhuiChina national geophysical observatory at mengcheng MengchengAnhuiChina

Accurate determination of seismic velocity of the crust is important for understanding regional tectonics and crustal evolution of the Earth. We propose a stepwise joint linearized inversion method using surface wave dispersion, Rayleigh wave ZH ratio （i.e., ellipticity）, and receiver function data to better resolve 1D crustal shear wave velocity （Vs） structure. Surface wave dispersion and Rayleigh wave ZH ratio data are more sensitive to absolute variations of shear wave speed at depths, but their sensi- tivity kernels to shear wave speeds are different and complimentary. However, receiver function data are more sensitive to sharp velocity contrast （e.g., due to the existence of crustal interfaces） and Vp/Vs ratios. The stepwise inversion method takes advantages of the complementary sensitivities of each dataset to better constrain the Vs model in the crust. We firstly invert surface wave dispersion and ZH ratio data to obtain a 1D smooth absolute vs model and then incorporate receiver function data in the joint inver- sion to obtain a finer Vs model with better constraints on interface structures. Through synthetic tests, Monte Carlo error analyses, and application to real data, we demonstrate that the proposed joint inversion method can resolve robust crustal Vs structures and with little initial model dependency.

关键词： Joint inversion Receiver function Surfacewave dispersion Rayleigh wave ZH ratio· Shearwave velocity

A method for inversion of layered shear wavespeed azimuthal anisotropy from Rayleigh wave dispersion using the Neighborhood Algorithm

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Earthquake Science 2015年第1期28卷 59-69页

作者： Huajian Yao Laboratory of Seismology and Physics of Earth’s Interior School of Earth and Space SciencesUniversity of Science and Technology of China national geophysical observatory at mengcheng

Seismic anisotropy provides important constraints on deformation patterns of Earth＇s material. Rayleigh wave dispersion data with azimuthal anisotropy can be used to invert for depth-dependent shear wavespeed azimuthal anisotropy, therefore reflecting depth-varying deformation patterns in the crust and upper mantle. In this study, we propose a two-step method that uses the Neighborhood Algorithm （NA） for the point-wise inversion of depth-dependent shear wavespeeds and azimuthal anisotropy from Rayleigh wave azimuthally anisotropic dispersion data. The first step employs the NA to estimate depth- dependent Vsv （or the elastic parameter L） as well as their uncertainties from the isotropic part Rayleigh wave dispersion data. In the second step, we first adopt a difference scheme to compute approximate Rayleigh-wave phase velocity sensitivity kernels to azimuthally anisotropic parameters with respect to the velocity model obtained in the first step. Then we perform the NA to estimate the azimuthally anisotropic parameters Gc/L and Gs/L at depths separately from the corresponding cosine and sine terms of the azimuthally anisotropic dispersion data. Finally, we compute the depth-dependent magnitude and fast polariza- tion azimuth of shear wavespeed azimuthal anisotropy. The use of the global search NA and Bayesian analysis allows for more reliable estimates of depth-dependent shear wavespeeds and azimuthal anisotropy as well as their *** illustrate the inversion method using the azimuthally anisotropic dispersion data in SE Tibet, where we find apparent changes of fast axes of shear wavespeed azimuthal anisotropy between the crust and uppermost mantle.

关键词： Azimuthal anisotropy Shear wavespeed Rayleigh wave Neighborhood Algorithm

Magnetic flux ropes in the solar corona: structure and evolution toward eruption

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Research in Astronomy and Astrophysics 2020年第10期20卷 287-328页

作者： Rui Liu CAS Key Laboratory of Geospace Environment Department of Geophysics and Planetary SciencesUniversity of Science and Technology of ChinaHefei 230026China CAS Center for Excellence in Comparative Planetology Hefei 230026China mengcheng national geophysical observatory University of Science and Technology of ChinaMengcheng 233500China

Magnetic flux ropes are characterized by coherently twisted magnetic field lines,which are ubiquitous in magnetized *** the core structure of various eruptive phenomena in the solar atmosphere,flux ropes hold the key to understanding the physical mechanisms of solar eruptions,which impact the heliosphere and planetary *** strongest disturbances in the Earth’s space environments are often associated with large-scale flux ropes from the Sun colliding with the Earth’s magnetosphere,leading to adverse,sometimes catastrophic,space-weather ***,it remains elusive as to how a flux rope forms and evolves toward eruption,and how it is structured and embedded in the ambient *** present paper addresses these important questions by reviewing current understandings of coronal flux ropes from an observer’s perspective,with an emphasis on their structures and nascent evolution toward solar eruptions,as achieved by combining observations of both remote sensing and in-situ detection with modeling and *** paper highlights an initiation mechanism for coronal mass ejections(CMEs)in which plasmoids in current sheets coalesce into a’seed’flux rope whose subsequent evolution into a CME is consistent with the standard model,thereby bridging the gap between microscale and macroscale dynamics.

关键词： magnetic fields magnetic reconnection Sun:magnetic fields Sun:corona Sun:coronal mass ejections(CMEs) Sun:flares Sun:filaments,prominences

Determination of the local magnitudes of small earthquakes using a dense seismic array in the Changning-Zhaotong Shale Gas field,Southern Sichuan Basin

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Earth and Planetary Physics 2021年第6期5卷 532-546页

作者： Wen Yang GuoYi Chen LingYuan Meng Yang Zang HaiJiang Zhang JunLun Li Laboratory of Seismology and Physics of the Earth’s Interior School of Earth and Space SciencesUniversity of Science and Technology of ChinaHefei 230026China national geophysical observatory at mengcheng University of Science and Technology of ChinaMengcheng Anhui 233500China China Earthquake Networks Center Beijing 100045China

With the development of unconventional shale gas in the southern Sichuan Basin,seismicity in the region has increased significantly in recent *** the existing sparse regional seismic stations can capture most earthquakes with ML≥2.5,a great number of smaller earthquakes are often omitted due to limited detection *** the advent of portable seismic nodes,many dense arrays for monitoring seismicity in the unconventional oil and gas fields have been deployed,and the magnitudes of those earthquakes are key to understand the local fault reactivation and seismic ***,the current national standard for determining the local magnitudes was not specifically designed for monitoring stations in close proximity,utilizing a calibration function with a minimal resolution of 5 km in the epicentral *** is,the current national standard tends to overestimate the local magnitudes for stations within short epicentral distances,and can result in discrepancies for dense *** this study,we propose a new local magnitude formula which corrects the overestimated magnitudes for shorter distances,yielding accurate event magnitudes for small earthquakes in the Changning-Zhaotong shale gas field in the southern Sichuan Basin,monitored by dense seismic arrays in close *** formula is used to determine the local magnitudes of 7,500 events monitored by a two-phased dense array with several hundred 5 Hz 3 C nodes deployed from the end of February 2019 to early May 2019 in the Changning-Zhaotong shale gas *** magnitude of completeness(MC)using the dense array is-0.1,compared to MC 1.1 by the sparser Chinese Seismic Network(CSN).In addition,using a machine learning detection and picking procedure,we successfully identify and process some 14,000 earthquakes from the continuous waveforms,a ten-fold increase over the catalog recorded by CSN for the same period,and the MC is further reduced to-0.3 from-0.1 compared to the catalog obtained via ma

关键词： shale gas development local magnitude microearthquakes dense seismic array machine learning

Interseismic slip distribution and locking characteristics of the mid-southern segment of the Tanlu fault zone

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Earthquake Research Advances 2024年第3期4卷 16-26页

作者： Shuyuan Yu Layue Li Jiaji Luo Yuanyuan Yang Anhui Earthquake Agency Hefei230031China Anhui mengcheng national geophysical observatory MengCheng200527China China University of Mining and Technology Xuzhou221116China The First Monitoring and Application Center Tianjin300180China

We employ the block negative dislocation model to invert the distribution of fault coupling and slip rate deficit on the different segments of the Tanlu(Tancheng-Lujiang) fault zone, according to the GPS horizontal velocity field from 1991 to 2007(the first phase) and 2013 to 2018(the second phase). By comparing the deformation characteristics results, we discuss the relationship between the deformation characteristics with the M earthquake in Japan. The results showed that the fault coupling rate of the northern section of Tancheng in the second phase reduced compared with that in the first phase. However, the results of the two phases showed that the northern section of Juxian still has a high coupling rate, a deep blocking depth, and a dextral compressive deficit, which is the enrapture section of the 1668 Tancheng earthquake. At the same time, the area strain results show that the strain rate of the central and eastern regions of the second phase is obviously enhanced compared with that of the first phase. The occurrence of the great earthquake in Japan has played a specific role in alleviating the strain accumulation in the middle and south sections of the Tanlu fault zone. The results of the maximum shear strain show that the shear strain in the middle section of the Tanlu fault zone in the second phase is weaker than that in the first phase, and the maximum shear strain in the southern section is stronger than that in the first phase. The fault coupling coefficient of the south Sihong to Jiashan section is high, and it is also the unruptured section of historical earthquakes. At the same time, small earthquakes in this area are not active and accumulate stress easily, so the future earthquake risk deserves attention.

关键词： Tanlu fault Middle-southern segment GPS velocity field Inter-seismic slip Fault couping Steepest descent method

Composition of high frequency ambient noise from cross-correlation:A case study using a small aperture array

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Earthquake Science 2010年第5期23卷 433-438页

作者： Weitao Wang Sidao Ni Baoshan Wang Institute of Geophysics China Earthquake Administration Beijing 100081 China mengcheng national geophysical observatory School of Earth and Space Science University of Science and Technology of China Hefei 230026 China

Long-time cross correlation of ambient noise has been proved as a powerful tool to extract Green＇s function between two receivers. The study of composition of ambient noise is important for a better understanding of this method. Previous studies confirm that ambient noise in the long period （3 s and longer） mostly consists of surface wave, and 0.25-2.5 s noise consists more of body waves. In this paper, we perform cross correlation processing at much higher frequency （30-70 Hz） using ambient noise recorded by a small aperture array. No surface waves emerge from noise correlation function （NCF）, but weak P waves emerge. The absence of surface wave in NCF is not due to high attenuation since surface waves are strong from active source, therefore probably the high ambient noise mostly consists of body wave and lacks surface wave. Origin of such high frequency body waves in ambient noise remains to be studied.

关键词： ambient noise cross correlation Green's function body wave high frequency

Processing Seismic Ambient Noise Data to Obtain Reliable Surface Wave Dispersion Measurements

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Earthquake Research in China 2015年第2期29卷 214-224页

作者： Li Lingli Wang Weitao Zhu Liangbao Chen Haopeng Wang Qingdong Miao Peng Wang Jun Earthquake Administration of Anhui Province mengcheng national geophysical observatory Institute of Geophysics CEA Department of Geophysics School of Geodesy and GeometricsWuhan University

Ambient noise tomography is a rapidly emerging field of seismological research. This paper presents the current status of ambient noise data processing and its development history over the past several years, with the intention to explain and justify this development through salient examples. The ambient noise data processing procedure can be divided into four principal phases： ① single station data preparation; ② cross- correlation and temporal stacking; ③ measurements of dispersion curves （ performed with frequency-time analysis for both group and phase speeds） ; ④ quality control, including SNR analysis and selection of the acceptable measurements. In addition, we provide a specific solution for a better use of the seismic station data to ambient noise study.

关键词： Seismic ambient noise Cross-correlation Rayleigh surface wave Dispersion curves