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Teleseismic shear wave splitting and intracontinental collision deformation of the northern Tibetan Plateau and the eastern Tarim basin

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Science China Earth Sciences 2023年第7期66卷 1556-1568页

作者： Lijun CHANG Chunyong WANG institute of geophysics China Earthquake AdministrationBeijing 100081China

Shear wave splitting measurement of teleseismic data has been used to determine the fast polarization directions and delay times for 38 temporary stations and 15 permanent stations from a NW linear seismic array across the eastern Tarim basin(ETB) and the northern Tibetan Plateau(NTP),and 10 permanent stations on both sides of the *** present an image of upper mantle anisotropy in the ETB and NTP using the 63 new *** results show that the fast directions and delay times have complex spatial distribution *** delay times within the interior of the Tarim basin are very small,with an average value of 0.6 s,which is not only smaller than that in the Altyn Tagh fault and Tianshan on the southern and northern margins of the basin,but also smaller than that in the NTP,reflecting that the delay time of stable blocks is smaller than that of active *** the array,from east to west,the fast directions contrarotate from NNW in the southern Songpan-Garze terrane to NW in the northern Songpan-Garze terrane,to near E-W or ENE in the north of the East Kunlun fault and southern margin of the Qaidam basin,then first abruptly rotate to NW in the Qiman Tagh fault on the northwestern margin of the Qaidam basin,second abruptly rotate to ENE in the Altyn Tagh fault and south of the ETB,and third abruptly rotate to NW in the north of the ETB,then finally rotate to WNW in the *** comparative analysis between the fast wave directions measured by shear wave splitting and predicted from the surface deformation field shows that,with the exclusion of the five observations with larger misfits within the interior of the ETB(with an average misfit of 27°),the misfits in the NTP and northern and southern margins of the Tarim basin are relatively small(with an average misfit of 9°).In addition,the fast wave directions of the tectonic units such as the Altyn Tagh fault,East Kunlun fault,and Tianshan are parallel to the strikes of faults and mountains i

关键词： Northern Tibetan Plateau Eastern Tarim basin Altyn Tagh fault East Kunlun fault Lithospheric deformation

A method for computing interstory drift spectra with consideration of gravity effects

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Earthquake Engineering and Engineering Vibration 2010年第4期9卷 513-521页

作者： Xie Junju Wen Zengping Hu Yuxian institute of geophysics China Earthquake Administration Beijing 100081 China

Vertical loads such as gravity may have an important influence on the seismic response of buildings. In this paper, the continuous shear-beam model is extended to study the seismic demand of shear buildings with consideration of the gravity load effect under near-field ground motions. An analytical solution of the free motion equation of as gravity shear beam model is provided in terms of a Bessel series. A method for computing interstory drift spectra is proposed. The interstory drift spectra for two near-field records with distinct pulses are presented to illustrate the effects of gravity and the damping ratio. The interstory drift spectra are also used to analyze the spectral characteristics of near fault ground motion during the 2008 Wenchuan earthquake. The effects of the gravity load ratio, damping ratio and higher modes are investigated and discussed.

关键词： cantilever shear-beam model gravity pulse drift spectrum Wenchuan earthquake Bessel series

Magnetic Properties of Street Dust from Chibi City,Hubei Province,China:Its Implications for Urban Environment

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Journal of Earth Science 2009年第5期20卷 848-857页

作者：刘庆生曾庆理杨涛邱宁 Chan Lungsang institute of geophysics and Geomatics China University of Geosciences institute of geophysics China Earthquake Administration Department of Earth Sciences University of Hong Kong

Magnetic measurements and heavy metal analyses were performed on street dusts from the main urban area of Chibi（赤壁） City,Hubei（湖北） Province,*** revealed that a PSD/MD（pseudo-single-domain/multi-domain） magnetite-like phase dominates the magnetic phases of the street ***-related magnetic parameters,such as magnetic susceptibility（χ）,anhysteretic remanent magnetization（ARM）,and saturation isothermal remanent magnetization（SIRM） of samples increased in the main roads but appeared lower in the landscape area of the Lushui（陆水） Lake and closely correlated with the concentration of heavy metal Fe,Cu,and Co,and the correlation coefficients are 0.786 for Fe-χ,0.548 for Cu-χ,and 0.580 for Co-χ,***,much strong correlations between SIRM and the concentrations of heavy metal suggest that SIRM is a better indicator for heavy metal pollution in the street dust in the study *** magnetic particles in the street dust are mainly derived from anthropogenic activities,such as vehicle emissions,abrasion of tires,coal combustion,cement works,and building *** results make it possible to use magnetic techniques as simple,rapid,and nondestructive tools for assessing the heavy metal pollutions in urbanization process.

关键词： environmental magnetism street dust heavy metal Chibi City.

Crustal structure beneath Qiangtang and Lhasa terrane from receiver function

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Acta Seismologica Sinica(English Edition) 2006年第6期19卷 633-642页

作者：李永华吴庆举田小波曾融生张瑞青李红光 institute of geophysics China Earthquake AdministrationBeijing 100081 China institute of Geology and geophysics Chinese Academy of SciencesBeijing 100029 China

To determine the crustal structure in central Tibet, we used teleseismic waveform data recorded by 18 stations in the INDEPTH-Ⅲ seismic array across the central Tibet from the central Lhasa terrane to the central Qiangtang terrane. The S-wave velocity structures beneath stations are determined by inverting the stacked radial receiver function using the GA method. The first order features in the receiver function are modeled. Our results show that the Moho in Qiangtang is about 8 km shallower than that in Lhasa terrane along the INDEPTH-Ⅲ profile. It maybe suggests the northward subduction of the Lhasa mantle lid beneath the Qiangtang terrane is affected by the India-Asia collision. We conclude that there exist low velocity zone in the middle crust across the northern Lhasa and Qiangtang terrane, which can be related to the high temperature upper mantle beneath that.

关键词： Tibetan Plateau receiver function low velocity zone crustal thickness

Why are Q-Ratios High in the Sulu UHP Metamorphic Rocks?

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Journal of Earth Science 2011年第1期22卷 115-116页

作者：刘庆生 institute of geophysics & Geomatics China University of Geosciences

I found high Q values （Q-ratio=Jn/Ji, .In, Ji are remanent magnetization and induced magnetization） in the Sulu ultrahigh pressure （UHP） metamorphic rocks, eastern China which is the world＇s largest UHP metamorphic belt （Fig. 1 in Liu et al., 2009）. Q values of 320 core samples with variable lithologies in the 100--2 000 m interval from the Chinese Continental Scientific Drilling （CCSD） main hole are as follows： values between 0.06 and 608.24, with an average of 15.56 for 171 eclogite samples;

关键词： UHP high Why are Q-Ratios High in the Sulu UHP Metamorphic Rocks

THE PRECURSOR OF INSTABILITY FOR NONLINEAR SYSTEMS AND ITS APPLICATION TO EARTHQUAKE PREDICTION

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Science China Chemistry 1991年第8期34卷 977-986页

作者：尹祥础尹灿 institute of geophysics State Seismological Bureau

By analysing the instability process of various nonlinear systems, we conclude that their instability precursors are the continual heightening of the response rate or response *** this theory to earthquake prediction, we adopt the periodical change of the stress in crust caused by the tide-generating force as the loading and unloading. If we can measure the ratio of the response (such as crust deformation, gravity and seismicity) during the loading period to that during the unloading period, this parameter must contain some characteristic information about the seismogenic *** nine earthquakes (M≥7) data that occurred in Chinese mainland during 1970-1988, we take the sum of square root o?energy of small earthquakes, which is called the released strain by Benioff, as the response to the tidal loading and unloading. We find that the response ratios of seven earthquakes increase obviously before the main earthquakes.

关键词： nonlinear system instability loading and unloading response ratio tidal stress in crust earthquake prediction.

The Crustal Structure and Seismic Activity in North China

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Acta Geologica Sinica(English Edition) 1989年第4期63卷 343-359,448-449页

作者： Feng Rui institute of geophysics, State Seismological Bureau, Beijing Huang Guifang, Zheng Shuzhen, Wang Jun, Yan Huifen Geophysical Prospecting Party, State Seismological Bureau, Zhengzhou, Henan and Zhang Ruoshui Seismological Technique College, State Seismological Bureau, Yanjiao,Hebei institute of geophysics State Seismological Bureau Beijing China

A layered crustal block model of North China has been constructed based on large amount of data from seismic sounding carried out in recent two decades. Some deep fault zones, such as the *** and Tancheng-Lujiang fault zones, divide the upper crust of North China into three upper crustal terranes and nine bolcks. There are distinct differences in velocity and depth distributions, which reflects Cenozoic block faulting in North China in the process of formation of the deep structure. The upper crust shows the features of transition in isostatic adjustment. The existence of a low-velocity layer in the middle crust is characteristic of the crustal structure in North China. There seems to be an increase of rheology of the rocks in the lower crust and a persistence of stable regional stress field. The patterns of the Moho on two sides of the Yanshan-Taihang Mountains are different. The relief of the Moho around Beijing, Shijiazhuang and Guangrao where the deep faults join together shows a quadrantal distribution in some degree. The dynamic sources for seismic activity are the NE-SW horizontal compression and the diapirism of the upper mantle. The middle and upper crust, especially the layered block structure has the most significant effects on seismicity, and the occurrence of earthquakes is more closely related to them than to the Moho.

关键词： The Crustal Structure and Seismic Activity in North China Activity

New paleomagnetic data confirm a dual-collision process in the Himalayas

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National Science Review 2015年第4期2卷 395-396页

作者： Wenjiao Xiao institute of Geology and geophysics Chinese Academy of Sciences

The India–Asia collision and continual plate convergence have created the Himalayan–Tibetan Orogen,which is the youngest and most spectacular continent–continent collision belt on Earth,and thus an ideal place for the study of continent–continent collisions[1,2].Although a large number of geological and geophysical investigations

关键词： data Asia Figure

Quantitative analysis of the relationship between polar ionospheric currents and auroral electrojet indices

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Science China Earth Sciences 2005年第3期48卷 376-383页

作者： XU Wenyao CHEN Gengxiong institute of Geology and geophysics Chinese Academy of Sciences Beijing 100029 China Institute of Geology and Geophysics Chinese Academy of Sciences Beijing 100029 China

The ionospheric currents in the polar region are caused mainly by field-aligned currents. The quiet polar current system consists of a pair of current vertices at dawn and dusk. When substorm occurs, however, intense magnetic disturbances are generated by enhanced polar currents, especially the westward electrojet of a millions Amperes in the auroral oval. The intensity of the auroral electrojet is commonly described by the auroral electrojet indices AL, AU, AE and AO. In this paper the relationship between the polar current system and the auroral electrojet indices is quantitatively studied by means of polar current functions obtained from the data recorded at 71 magnetic stations in the northern polar region during the International Mag- netospheric Study (IMS). Fairly well linear correlation of AL (or AU) with AE index has been found, indicating that AE index multiplied by a proper factor can approximately substitute AL and AU indices. The total polar current, JT, and the strengths of the dawn and dusk current vortices, JT 1 and JT , can be characterized by AE index, an increment of 1nT in AE index corresponding to 2 1000A in JT. A fairly well direct proportion is found between AE and the maximal westward current density, an increment of 1 nT in AE corresponding to 1 A/km of the maximal westward current density at magnetic midnight. The latitudinal profiles of the current density are similar for different local time in night sector. The maximal density of the westward electrojet usually occurs at geo- magnetic latitude 65°—70°around midnight, as for the eastward electrojet, it is around 80°. The analysis shows that for 5-mimute mean values, the saturation values of AE and AL are 700 nT and –500 nT, respectively. Accordingly, a caution should be taken when the indices greater than the saturation values would be used for studying magnetospheric or ionospheric processes.

关键词： polar current system, auroral electrojet, auroral electrojet indices, magnetic disturbance.