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Partial Melting and Its Implications for Understanding the Seismic Velocity Structure within the Southern Tibetan Crust

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Acta Geologica Sinica(English Edition) 2003年第1期77卷 64-71页

作者： YANG Xiaosong, MA Jin, JIN Zhenmin, gao Shan and MA Shengli Geology Institute, china seismological bureau, beijing 100029 Laboratory of Tectonophysics, china seismological bureau, beijing 100029 Faculty of Earth Sciences, china University of Geosciences, Wuhan, Hubei 430074 china Seismol Bur Inst Geol Beijing 100029 Peoples R China china Seismol Bur Lab Tectonophys Beijing 100029 Peoples R China china Univ Geosci Fac Earth Sci Wuhan 430074 Hubei Peoples R China

In order to constrain the crustal wave velocity structure in the southernTibetan crust and provide insight into the contribution of crustal composition, geothermal gradientand partial melting to the velocity structure, which is characterized by low average crustalvelocities and widespread presence of low-velocity zone(s), the authors model the crustal velocityand density as functions of depth corresponding to various heat flow values in light of velocitymeasurements at high temperature and high pressure. The modeled velocity and density are regarded ascomparison standards. The comparison of the standards with seismic observations in southern Tibetimplies that the predominantly felsic composition at high heat flow cannot explain the observedvelocity structure there. Hence, the authors are in favor of attributing low average crustalvelocities and low-velocity zone(s) observed in southern Tibet mainly to partial melting. Modelingbased on the experimental results suggests that a melting percentage of 7-12 could account for thelow-velocity zone(s).

关键词： partial melting intracrustal low-velocity zone high-pressure andhigh-temperature experiments Tibetan plateau

Analysis on Source Process of Strong Earthquakes in Qinghai Province Based on Broadband Data

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Earthquake Research in china 1998年第3期12卷 17-23页

作者： gao Yuan, Wu Zhongliang, and Zhou HuilanGraduate School of USTC, Academia Sinica, beijing 100039, chinaCenter for Analysis and Prediction, china seismological bureau, beijing 100036, chinaInstitute of geophysics, china seismological bureau, beijing 100081, china

Four earthquakes with M > 6.0 occurred in Qinghai Province, china froth 1988 to 1990. Using broadband data from GDSN, the source ruptures of these earthquakes and tectonic surroundings were studied using waveform modelling combined with background data of geological tectonics. Through the analysis of apparent source time function (aSTF) and apparent time difference (aTD), the complexity of sources was discussed, and in view of source analysis, the result further supports the conclusion that the compressive stress axis of tectonic stress field in northeastern Qinghai-Xizang (Tibetan) plateau is at the NE direction, is nearly horizontal, turns counter-clockwise to the NEE or N to S direction, and is nearly horizontal close to the northern Qinghai-Xizang plateau.

关键词： Qinghai-Xizang (Tibetan) plateau Source process Rupture Apparent source time function (aSTF) Apparent time difference (aTD).

Preliminary Study on Probabilistic Prediction of Seismic Hazard in a Period of 10 Years

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Earthquake Research in china 1995年第4期9卷 10-17页

作者： gao Mengtan and Wang JianInstitute of geophysics,SSB,beijing 100081,china

Many uncertainty factors need be dealt with in the prediction of seismic hazard for a 10-year *** by these uncertainties,the result of prediction is also uncertain to a certain extent,so the probabilistic analysis method of seismic hazard should be *** consideration of the inhomogeneity of the time,location,and magnitude of future earthquakes and the probabilistic combination of the background of long-term seismic hazard(geology,geophysical field,etc.)and the precursors of earthquake occurrence,a model of probabilistic prediction of seismic hazard in a period of 10 years s *** the inhomogeneity of data and earthquake precursors for different regions in china,a simplified model is also proposed in order to satisfy the needs of different regions around the country.A trial in North china is used to discuss the application of the *** method proposed in this paper can be used in the probabilistic prediction of seismic hazard in a period of 10 *** to

关键词： probability model medium-term prediction

Seismic Zoning Methods That Assume Spatially Non-Uniform Earthquake Distribution in the Potential Source:Their Application to Western Panzhihua and Central and Southern Shanxi Province

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Earthquake Research in china 1997年第4期11卷 81-88页

作者： gao Mengtan and Xu GuangyinInstitute of geophysics,SSB,beijing 100081,china

Based on the models of non-uniform earthquake distribution in the potential source,the seismic zonation of Western Panzhihua and Central and Southern Shanxi Province is *** results show that the usual uniform distribution model may underestimate the seismic risk and result in a reduction of the areas of high *** influence of each non-uniform probabilistic distribution method on the result of seismic zoning is discussed.

关键词： seismic zonation probabilistic nonhomogeneous distribution.

Intensifying Earthquake Prediction in the Light of Action of International Decade for Natural Disaster Reduction

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Earthquake Research in china 1995年第2期9卷 87-93页

作者： gao Wenxue and gao QinhuaState seismological bureau,beijing 100036,china Institute of Geology,SSB,beijing 100029,china

This paper is a review on earthquake prediction and forecast research,progress in earthquake prediction work and pre-estimation of earthquake hazard degree in china in recent *** indicates that china is the first country,the government of which has promoted and organized the state administration department on reduction of seismic hazards and ensured the socialization of earthquake prediction and forecast in the world.A program of earthquake prevention and protection and hazard reduction based on the results of research on earthquake occurrence regularities and prediction of earthquake preparation trend has been completed,and hence the socialization of results of earthquake prediction and forecast research can be expected to be in *** practical seismological works in last 20 years indicate that the earthquakes are not considered to be unpredictable,but it is a challenge remaining to be *** are willing to cooperate with all friends who are engaged in earthquake prediction and

关键词： Seismic feature Earthquake prediction Earthquake disaster prediction Chinese mainland

Confidence Evaluation of Medium-and Long-Term Earthquake Prediction by Use of the Analytical Hierarchy Process

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Earthquake Research in china 1996年第2期10卷 69-79页

作者： Wang Xiaoqing and gao MengtanCenter for Analysis and Prediction, SSB, beijing 100036, china Institute of geophysics, SSB, beijing 100081, china

This paper offers an approach to the relative confidence level of medium- and long-term earthquake prediction methods by use of the analytical hierarchy process (AHP). We construct the criterion judgment matrices according to the results of an expert questionnaire known as the Delphi scheme. From the matrices we can obtain a scale for the relative preference or priority weight of each factor. The quantitative weights might be applied to make synthetic prediction of earthquake risk areas in the northern part of the North china seismic region.

关键词： Seismic analysis Confidence level Prediction version.

NEWLY GENERATED SEISMOTECTONIC ZONES IN NORTH china AND ITS REGIONAL SEISMOTECTONIC FRAMEWORK

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Scientia Geologica Sinica 2001年第3期 159-168页

作者： Xu Jie, gao Zhanwu and Song Changqing Institute of Geology, china seismological bureau, beijing 100029,china

In North china, the tectonic environment and the stress state of the Neotectonic period (N-Q) are obviously different from those of Palaeogene, so there developed two types of active tectonic zones: inherited and newly generated. They are generally seismotectonic *** important newly generated seismotectonic zones such as Tangshan-Hejian-Cixian, Jiexiu-Xinxiang-Liyang and Yellow River Mouth-Liaocheng are preliminarily determined. The seismotectonic characters of the Zhangjiakou-Penglai and Tancheng-Lujiang inherited fault zones are analyzed. It is the two types of seismotectonic zones that form the regional seismotectonic framework of North china that we reestablished. It consists of more than 10 newly generated or inherited seismotectonic zones. It is in fact a new crustal conjugate shear fracture system. Future earthquakes of magnitude over 6 are expected to be controlled by this regional seismotectonic framework.

关键词： NEWLY GENERATED SEISMOTECTONIC ZONES IN NORTH china AND ITS REGIONAL SEISMOTECTONIC FRAMEWORK ITS

Heterogeneous Features of Temporal and Spatial Variation of Earthquake Occurrence in Process of Earthquake Preparation

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Earthquake Research in china 2001年第1期15卷 47-56页

作者： Huang Yun , gao Xu and Xie Huazhangseismological bureau of Jiangsu Province, Nanjing 210014, china seismological bureau of beijing Municipality, beijing 100080, china seismological bureau of Jiangsu Province Nanjing 210014 China Seisrnological bureau of beijing Municipality Beijing 100080 China

By applying the GL-value, a parameter describing the heterogeneities in temporal and spatial distribution of moderate and small earthquakes prior to strong earthquakes, the following problems have been studied in the present paper: a systematic investigations have been made on the features of spatial distribution and temporal variation of the high value anomalies ( GL ≥1.0) prior to 28 moderately strong earthquakes with Ms ≥5.0 in the North china region; a systematic study has been made on the reasonability of the lower limit of magnitude, the time window and the space window for calculations at various seismicity levels in this region; the parameters taken in the calculation have been optimized and modified; the anomalous variations of GL-value prior to various moderately strong earthquakes in North china region have been investigated and followed, using the total time-space scanning method. The results of the study have shown that for 82 % of the moderately strong earthquakes in the North china region, obvious anomalous region with high GL-values appears near the future epicenter about 1 ～ 3.5 years before the earthquakes. The earthquakes usually occur in the marginal area of the anomalous zone or near it. Temporal variations of the GL-values in the anomalous zone show that the duration of anomalous ranges between 3 ～ 25 months with a predominant interval of 5 ～ 19 months, into which about 70% the total anomalies fall. The predominant interval of earthquake occurrences is 0 ～ 14 months after ending of the anomaly, into which about 83 % of the total anomalies fall. Based on these results the GL-value method is considered to be a rather effective prediction method for moderately strong earthquakes in the North china region.

关键词： Seismicity Heterogeneity GL-value

TRANSPORTATION THEORY OF MULTIPLE SCATTERING AND ITS APPLICATION TO SEISMIC CODA WAVES OF IMPULSE SOURCE

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Science in china,Ser.B 1988年第12期31卷 1503-1514页

作者：尚铁樑高龙生 Department of Applied Physics Harbin Engineering University Institute of geophysics State seismological bureau beijing

The energy distribution of elastic waves in an infinite elastic medium with uniformly and randomly distributed scatterers has been researched. The scattering process is assumed to be isotropic and without conversions between wave types. We get the equation on the distribution of energe density in time and space covering single as well as multiple scattering. Taking physical symmetry of the field into account, it can be simplified. In the case of small earthquakes, the energy source of elastic waves can be assumed as a short pulse emitted isotropically at t=0. The first-order approximate solution in the 3-dimensional space can be obtained, and it is equivalent to Sato’s solution for single scattering. In the 2-dimensional space the complete analytical solution has been derived by the mathematical inductance which leads to a conclusion that the codas of surface waves can give the Q-factor related to intrinsic absorption. The equation obtained in this paper is more general.

关键词： coda scattering seismic wave maltiple scattering Q-factor.