China National Report on Seismology and Physics of the Earth's Interior
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2003-2006 China National Report on Seismology and Physics of the Earth's Interior For The 24rd General Assembly of IUGG Perugia, Italy, 2-13 July, 2007 By Chinese National Committee for The International Union of Geodesy and Geophysics Beijing, China June, 2007 Preface During the last four years there have been significant advances in China, a country with intense seismic activity and earthquake disasters, in the study of seismology and physics of the Earth’s interior. These results are of significant help to the social endeavor for the reduction of earthquake hazard and risk, and potentially have an important impact on the development of seismology and solid-Earth geophysics even in a global perspective. Besides the continuous advancements in the on-going researches on seismic source, seismic waves, earthquake prediction, seismo-tectonics, Earth structure and geodynamics, and interdisciplinary studies related to the phenomenology and physics of earthquakes, among others, in the turn of the centuries, the development of seismology in China is specially highlighted by its comprehensive upgrading of observation/research facilities as marked by the digital broadband seismograph networks and data centers at national, regional and local levels, and the geodynamical modeling using high-performance computation. The present National Report, organized by the Chinese National Committee for the International Association of Seismology and Physics of the Earth’s Interior (IASPEI), reviews the developments in seismology in the Chinese mainland from 2003 to 2007. In China, at present, most of the publications are in Chinese (with English or Russian abstract), although quite a few Chinese seismologists also publish their researches in international journals. Accordingly, the National Report is of special importance for letting international colleagues understand what is going on in the seismological studies in China. It is worth acknowledging that contributions to seismological researches from the Chinese seismologists in Taiwan and Hong Kong, as well as from the overseas Chinese seismologists all over the world, are also significant, which are not reflected in the present national reports due to limitation of space and time. Cooperation between seismologists in the Chinese mainland and other places got fruitful results in many aspects. Seismology as a tool of prospecting the lithosphere and crust structure also contributed much to the study of fundamental geology and the development of oil industry. What is reflected in the present report is only the study of seismo-tectonics in the perspective of the geology and geodynamics of earthquakes. During the last four years, seismological researches in China got significant supports from the National Natural Science Foundation of China (NSFC), the Ministry of Science and Technology (MOST), the China Earthquake Administration (CEA), and the Chinese Academy of Sciences (CAS), as well as other governmental and non-governmental organizations, especially from the central government. The cooperation with IUGG, IASPEI, Asian Seismological Commission (ASC), and other international organizations, plays an active role in promoting the international exchange and collaboration between seismologists in China and other countries. DING Zhifeng, Chairman CHEN Xiaofei, Vice-Chairman Chinese National Committee for IASPEI Beijing, China IASPEI National Report (2003~2006) Studies of the Physics of Seismic Source in China XU Li-sheng, FENG Wan-peng, CHEN Yun-tai (Institute of Geophysics, China Earthquake Administration, Beijing 100081, China ) Abstract : On a basis of the papers published in the Chinese geoscience journals,this paper summarizes the research activities in the physics of seismic source that happened in the years 2003 to 2006 in China. The research works are presented in 6 fields, which are source complexity of the strong earthquakes, source parameters of moderate-to-small earthquakes, application of source parameters, earthquake location, theory and experiment on seismic source, as well as nuclear explosion seismology. Introduction Physics of seismic source is one of the important components of seismology, also it is one of the most active frontier fields of geophysical research. In the period of 2003 to 2006 years, more than 40 papers regarding the physics of seismic source were published on Chinese geoscience journals. In this article, we make a summary as the followings, which are divided into 6 parts: source complexity of the strong earthquakes, source parameters of the moderate-to-small earthquakes, application of the source parameters, earthquake location, theory and experiment on seismic source, as well as nuclear explosion seismology. 1. Source complexity of the strong earthquakes Rupture process or source complexity of stronger earthquakes have been paid much attention to by the world-wide seismologists due to its importance to understanding physics of seismic source. Chinese seismologists have been become active in this direction. Although several years have passed since the 1999 Chi-Chi earthquake, and some studies had been done, some studies have still been done, for example, Zhou and Chen (2006) inverted the near-field seismic recordings for the dynamic rupture process of this earthquake. On the 14th of November, 2001, there occurred a strong earthquake in the western pass of Kunlun Mountain in China. In order to understand the source physics of this earthquake, varieties of research works have been done by Chinese researchers. Xu and Chen (2004) inverted the long-period waveform data recorded by global seismic stations and obtained the rupture process. Also, Ma and Shan (2006) analyzed the InSAR data, and Wang et al . (2005) inverted both the GPS and far-field P waveform data. On the 27th of September, 2003, there occurred another strong earthquake of MS7.9 on the border area of China, Russia and Mongolia, and on the 1st of October in the same year, one stronger earthquake with magnitude MS7.3 occurred almost at the same location. Zhao et al. (2005) inverted the broadband recordings from global seismic stations for their dynamic rupture process. On the 11th of July, 2004, an MW 6.2 earthquake occurred in Tibet. Li et al . (2005) obtained its rupture process by the inversion technique similar to the above. 1 2. Source parameters of the moderate-to-small earthquakes Determination of parameters for moderate-to-small earthquakes is a difficult but important work. In China, there are a quite number of researchers working on this. Yu et al . (2003) introduced the amplitude ratios of SV/P, SH/P and SV/SH into the method for determination of focal mechanism in order to obtain the results of higher precision. Cheng et al . (2003) studied the MS5.0 foreshock, MS6.0 mainshock and the whole earthquake sequence which occurred in Yajiang county of Sichuan province in February of 2001 for their focal mechanisms, parameters of source spectrum, variation of stress drop and seismicity of the epicentral area. Qin et al . (2003) analyzed th the MS6.4 earthquake sequence for its physical process which occurred on the 15 of January, 2000, in Yaoan of Yunnan province using seismic recordings from a near-field small-apature network. Long (2004) choose the recordings of 88 events of the Yajian earthquake sequence clearly recorded by at least 5 stations, which occurred during the period of the 1 st of January to the 30 th of June, 2001, relocated these events and determined the focal mechanisms of the 13 bigger events. Wu et al . (2004) inverted the waveform data of 33 moderate-to-small local earthquakes from the Yunnan Digital Seismograph Network for their focal mechanisms. Kang et al . (2005) applied the first-motion-and-amplitude-ratio technique to the recordings of 32 local earthquakes greater than ML3 recorded by Guangdong Digital Seismograph Network for their focal mechanisms, and analysized the spatial characteristics of the focal mechanisms in Guangdong and its neighboring areas combining the focal mechanisms of 83 events obtained by others. Mao et al . (2006) inverted the direct P waveforms of the vertical components generated by the 2000 Yaoan MS6.5 mainshock and its aftershocks with magnitudes of ML3.0~5.0 for their moment tensor solutions. Gao et al . (2005) presented the spatial distribution of hazard caused by the Inner th Mongolia MS5.9 earthquake which occurred on the 16 of August, 2003, inverted the long period waveform data recorded by China Digital Seismograph Network for its moment tensor solution and focal mechanism, and analysized for the characteristics of the focal mechanism, aftershock distribution and hazard distribution and the relationship between the focal mechanism and the hazard distribution. Gao and Zheng (2004) obtained the quality factor (Q value) and the anelastic attenuation coefficients for the central and western Inner Mongolia from the seismic recordings generated by 9 earthquakes and recorded by the Hohhot Digital Seismograph Network. Wang et al . (2004) obtained the source spectrum at the lower frequencies for 27 earthquakes and the site effects in the central area of the Central China by means of genetic algorithm. There occurred an MS6.8 earthquake on the 24th of February, 2003, at the southeastern end of the Jiashi region, Xinjiang, where 9 earthquakes of about MS6.0 occurred in the period of 1997 to 1998. Gao et al .(2004) analyzed the characteristics and stress drop using the focal mechanisms of this sequence. Chuo et al . (2004) studied the anelastic attenuation