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Deep electrical structure of the Sulu orogen and neighboring areas

Science China Earth Sciences 2009年第3期52卷 420-430页

作者： XIAO QiBin ZHAO GuoZe WANG JiJun ZHAN Yan CHEN XiaoBin TANG Ji CAI JunTao WAN ZhanSheng WANG LiFeng MA Wei ZHANG JiHong Institute of Geology China Earthquake AdministrationBeijing 100029China earthquake administration of Shandong province Jinan 250014China

Because of the discovery of ultrahigh pressure metamorphic (UHPM) belt beneath the Sulu (Jiangsu province-Shandong province) orogen, this area has become a focused subject of current geoscience, as it has a close relationship with the evolution of the orogen and the neighboring North China craton. Probing the deep structure beneath this area would be of great significance for the geological interpretation of this issue. In this study, we make an analysis of magnetotelluric (MT) data along a profile across the Sulu orogen to provide evidence of deep structure below this region. The profile begins in west from the North China block, extending in S129°E, across the Tan-Lu fault, Sulu UHPM zone, and Sulu high pressure metamorphic (HPM) zone, and terminates in the Yangtze block in east. We use the nonlinear conjugate gradient method and TE-TM combined mode to perform inversion and interpretation of the MT data, and obtain an electrical structure image above depth of 150 km along the profile. It shows that the structure can be divided into seven sections in lateral direction, between which the electric boundaries coincide well with the major faults, such as the Tan-Lu, Haizhou-Siyang, and Jiashan-Xiangshui faults. In vertical direction the electrical structure can be subdivided into six layers of different resistivities. It is noted that there exist high-conductivity areas in crust below the North China block and Yangtze block, while such a feature is not present beneath the Sulu orogen, which is very different from the Dabie orogen. It is also observed that a fairly continuous zone of relatively low-resistivity exists at depths of 50–90 km of the electrical structure image, which is presumably a weak zone in the uppermost mantle. Just below this low-resistivity zone are the relatively high- resistivity layer of the North China block, relatively low-resistivity layer of the Sulu orogen, and relatively high-resistivity layer of the Yangtze block, all in the shallow upper m

关键词： ultrahigh pressure metamorphic belt deep electrical structure magnetotelluric sounding Sulu orogen and its neighboring areas

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Observation and analysis of geomagnetic abnormity associated with the M_S=5.7 Jiu-jiang-Ruichang earthquakeb

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Acta Seismologica Sinica(English Edition) 2006年第6期19卷 658-669页

作者：顾左文张毅姚同起高金田刘欣陈斌詹志佳顾春蕾 Institute of Geophysics China Earthquake AdministrationBeijing 100081 China earthquake administration of Anhui province Hefei 230031 China

A three-component geomagnetic survey was carried out during the period from 2002 to 2004 in China including Jiujiang-Ruichang region. Comparing the ＂2005.0 surface spline model of China geomagnetic field＂ created on the basis of the survey data with the ＂1970.0 surface spline model of China geomagnetic field＂, we can see an obvious abnormity in the geomagnetic horizontal component within a range of about 100 km around the epicenter of the Ms=5.7 Jiujiang-Ruichang earthquake occurred on November 26, 2005. After the earthquake, we carded out a repeated geomagnetic survey at 21 stations in the Jiujiang-Ruichang region and created a corresponding ＂2005.0 partially revised surface spline model of China geomagnetic field＂. By comparing the above three models, analyzing the geomagnetic horizontal component at the profile in the Jiujiang-Ruichang region and quantitatively studying the geomagnetic data of every stations around the Ms=5.7 earthquake, we have obtained the geomagnetic abnormity associated with this earthquake. Then the geomagnetic abnormity and its relation with seismic activity are discussed in this paper.

关键词： geomagnetic survey surface spline model geomagnetic anomaly Ms=5.7 Jiujiang-Ruichang earthquake

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Region-time-length algorithm and its application to the study of intermediate-short term earthquake precursor in North China

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Acta Seismologica Sinica(English Edition) 2004年第2期17卷 164-176页

作者：蒋海昆侯海峰周焕鹏周翠英 earthquake administration of Shandong province Ji'nan 250014China Laboratory of Tectonophysics China Earthquake AdministrationBeijing 100029China

The Region-Time-Length Algorithm (RTL algorithm) is introduced and improved in the paper. Compared with the original definition, the influence of rupture length on RTL function is emphasized and the weights of epicentral distance function, time function, and rupture length function are ensured to be equal. The retrospective examinations of RTL algorithm in North China have indicated that the anomalies obtained by the improved RTL algorithm show the short or intermediate-short term precursory features in most cases. There are two types of RTL anomalous patterns before the main shock. For the I-type, the variation pattern of the VRTL, numerical values of the VRTL(x, y, z, t) function, is complete and most of them have shown the changing pattern of rising from 0 turning dropping or dropping from 0 turning rising. For the II-type, the variation pattern of VRTL is not complete, which increases or decreases quickly from 0 and there is no evident turning, the main shock generally occurs in the short period around the peak VRTL. The rising of VRTL indicates an increase of seismic activity relative to the background level, which means the enhancement of seismic activity, while the dropping of VRTL indicates the decrease of seismic activity relative to the background level, which represents the seismic quiescence to a certain extent. According to statistical examination results of RTL algorithm in North China, the methods to distinguish the intermediate and short-term anomalies and to estimate the occurrence time of the coming main shock are given in the paper. For both I and II-type RTL anomalies, the R-value, i.e., the forecasting score, is about 0.6 and 0.3 for the 3 months forecasting period and about 0.7 and 0.4 for the 6 months forecasting period. The preliminary discussion is also made for the influences of characteristic time-span t0, characteristic distance r0, and threshold magnitude M0 on computation of VRTL, as well as some other significant problems in applic

关键词： RTL algorithm epicentral distance function time function rupture length function seismic activity level North China

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Basement interface structural characteristics beneath Jiashi strong earthquake swarm area in Xinjiang, China

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Acta Seismologica Sinica(English Edition) 2007年第5期20卷 507-512页

作者：徐朝繁段永红田晓峰潘纪顺张建狮胡修奇 Geophysical Exploration Center China Earthquake Administration earthquake administration of Henan province

The seismic data obtained from high resolution seismic refraction profile in Jiashi strong earthquake swarm area in Xinjiang, China were further processed with ray hit analysis method and more complete basement interface structural characteristics beneath Jiashi strong earthquake swarm area were determined. The results show that there are two clear basement interfaces at the upper crust in Jiashi strong earthquake swarm area. The first one with buried depth ranging from 2.6 km to 3.3 km presents integral and continuous structure, and it appears an inclined plane interface and smoothly rises up toward Tianshan Mountain. The second basement interface with buried depth from 8.5 km to 11.8 km, is the antiquated crystalline basement of Tarim basin. Near the post number of 37 km, the buried depth of the crystalline basement changed abruptly by 2.5 km, which maybe result from an ultra crystalline basement fault. If taking this fault as a boundary, the crystalline basement could be divided into two parts, i.e. the southwestern segment with buried depth about 11.5 km, and the northeastern segment with buried depth approxi-mately from 8.5 km to 9.0 km. That is to say, in each segment, the buried depth changes not too much. The northeast segment rises up as a whole and upheaves slightly from southwest to northeast, which reflects the upper crustal deformation characteristics under the special tectonic background at the northwestern edge of Tarim basin.

关键词： Jiashi strong earthquake swarm area high resolution refraction survey ray hit analysis method basement interface structure, ultra crystalline basement fault

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Rupture parameters of three MS≥5.0 Ludian, Yunnan, earthquakes

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earthquake Science 2008年第1期21卷 98-104页

作者：阮祥程万正 Lanzhou Institute of Seismology China Earthquake Administration earthquake administration of Sichuan province

Introduction Identifying rupture directions of earthquakes is one of important aspects in focal mechanism research. For moderate-strong events, at present, directions of their main ruptures are usually extrapolated from focal mechanism solutions by combining information about distributions of aftershocks and surface ruptures, or/and extends of iso-seismal major axes. However,

关键词： earthquake rupture focal mechanism Ludian earthquakes

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Compressive stress field in the crust deduced from shear-wave anisotropy: an example in capital area ofChina

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Chinese Science Bulletin 2008年第18期53卷 2840-2848页

作者： GAO Yuan WU Jing Institute of earthquake Science China Earthquake Administration Beijing 100036 China earthquake administration of Jiangsu province Nanjing 210014 China

The rocks in the crust are pervaded by stress-aligned fluid-saturated microcracks, and the complex fault tectonics and stress control the configuration of the microcracks, however shear-wave splitting could indicate this kind of characteristics. In this paper, Capital Area Seismograph Network (CASN), the widest scope and highest density of regional seismograph network presently in China, is adopted to deduce the principal compressive stress field distribution pattern from polarizations of fast shear- waves, based on shear-wave splitting analysis. The principal compressive stress in capital area of China is at NE85.7°± 41.0° in this study. Compared with the results of principal compressive stress field in North China obtained from other methods, the results in this study are reliable in the principal com- pressive stress field distribution in capital area. The results show that it is an effective way, although it is the first time to directly obtain crustal stress field from seismic anisotropy. It is effectively applied to the zones with dense seismograph stations.

关键词：地震带压缩力地震波地震学

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Geometric structure and formation mechanism of Lintong-Chang’an fault zone

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earthquake Science 2008年第2期21卷 156-169+220页

作者：师亚芹冯希杰戴王强李晓妮任隽种瑾 earthquake administration of Shaanxi province earthquake administration of Shaanxi province Xi’an 710068 China Xi’an 710068 China

The results from investigation of large quantity of fault outcrops and artificial earthquakes suggest that the Lin-tong-Chang’an fault zone mainly consists of two faults. One is the Majie-Nianwan fault that separates a branch of Wangjiabian-Houjiawan fault on the right bank of the Bahe River; the other is the Hujiagou-Shoupazhang fault that separates a branch of Zhongdicun-Tangjiazhai fault in Tongrenyuan and Shaolingyuan. As tensional dip-slip normal faults, the faults distribute with approximately parallel equal intervals in local regions and the profiles drop in a step-like form to the northwest, presenting a Y-shape combination. The result from deep seismic reflection indicates that the fault is about 5;km in depth, which is not only a basement fault, but also a listric normal fault in the deep stratum. The Lintong-Chang’an fault is a typical outstretching rift system under the NS-trending ten-sion stress field. At the same time, affected by the sinistral strike slip of the Yuxia-Tieluzi fault, the fault extends like a broom from the northeast to the southwest.

关键词： Lintong-Chang’an fault tension stress outstretching rift system listric normal fault

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Correlation analysis and causality test between Ludong-Huanghai block and South Japan

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Acta Seismologica Sinica(English Edition) 2007年第4期20卷 381-391页

作者：郑建常蒋海昆 earthquake administration of Shandong province China earthquake Networks Center

In this paper, we make a comparative analysis and correlation test for the seismic activities in the South Japan and the Ludong-Huanghai block （a secondary tectonic unit in the North China） and approach the relationship between the energy release processes of these two areas by using co-integration analysis and Granger causality test for the time series of random variables. The results show that the seismic activities in these two areas are correlative and synchronous to a certain extent, and their release series of cumulative strain energy are contemporaneously correlative. Both energy series are first-order difference stationary processes and there is secular and steady co-integration between them. We make a positive analysis on the first-order difference energy series through Granger causality test based on vector error correction （VEC） model and find there is unilateral Granger causality and prominent co-integration between the two energy release processes.

关键词： South Japan Ludong-Huanghai block correlation co-integration analysis Granger causality test

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Comparison of VP broadband tiltmeter and VS vertical pendulum tiltmeter

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Geodesy and Geodynamics 2015年第3期6卷 226-232页

作者： Ma Wugang Wu Yanxia Zhao Huiqin Key Laboratory of earthquake Geodesy Institute of Seismology China Earthquake Administration Wuhan Base of Institute of Crustal Dynamics China Earthquake Administration Yixian Seismic Station Earthquake Administration of Hebei Province

Vertical pendulum(VP) tiltmeter is a kind of earthquake precursor observation equipment,which is used to record the interaction force associated with astronomical tidal tilts caused. Currently, VP broadband tiltmeter and vertical sensor(VS) vertical pendulum tiltmeter are primarily used. In this paper, we compare the two different instruments by using four aspectsdmechanical structure, circuitry, zeroing, and bandwidthdbased on their working principles and applications. We conclude that VP broadband tiltmeter is more superior compared with VS vertical pendulum tiltmeter because of its higher bandwidth and degree of automation.

关键词： VP broadband tiltmeter Broadband VS vertical pendu

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Seismic reflection and transmission coeffi-cients at an air-water interface of saturated porous soil

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Acta Seismologica Sinica(English Edition) 2006年第4期19卷 397-405页

作者：周新民夏唐代徐平邹振轩 Institute of Geotechnical Engineering Zhejiang University earthquake administration of Zhejiang province

Based on the modified Biot＇s theory of two-phase porous media, a study was presented on seismic reflection and transmission coefficients at an air-water interface of saturated porous soil media. The major differences between air-saturated soils and water-saturated soils were theoretically discussed, and the theoretical formulas of reflection and transmission coefficients at an air-water interface were derived. The characteristics of propagation and attenuation of elastic waves in air-saturated soils were given and the relations among the frequency, the angle of incidence and the reflection, transmission coefficients were analyzed by using numerical methods. Numerical results show that the propagation characteristic of the wave in air-saturated soils is great different from that in water-saturated soils. The frequency and the angle of incidence can have great influences on the reflection and transmission coefficients at interface. Some new cognition about the wave propagation is obtained and the study suggests that we may carefully pay attention to the influence of air on the dynamic analysis of seismic wave.

关键词： seismic wave air-saturated soils propagation characteristics reflection and transmission

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