13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Applications of Fracture Theory to Instability Co-seismic Fault Problem TianYou Fan1,*, ZhuFeng Sun1, ZhongLei Du1, YaoLin Shi2 , BoJing Zhu2,3,* 1 Beijing Institute of Technology, Beijing 100081,CHINA 2 Key Laboratory of Computational Geodynamics of CAS, University of Chinese Academy of Sciences, Beijing 100049, CHINA 3 Rock Mechanics Laboratory, University of Durham, Durham DH1 3LE, UK * Corresponding author: tyfan2006@yahoo.com.cn(T.Y.Fan); cynosureorion@ucas.ac.cn (B.J.Zhu) Abstract: Co-seismic earthquake faults can be treated as cracks of fracture theory in the framework of continuum mechanics. It is well known that the instability of the faults leads to earthquakes, and the relevant problem can be explored through the fracture theory. There are many factors influencing the instability such as tectonic stresses, geology structure and so on. In this work, we discuss the effects of geometry, interaction between faults and the speed of nucleation and co-seismic process. For single fault, the closed formulations of fracture theory is simpler; for two collinear faults, the analytic solution is available; while for two parallel faults the semi-analysis is approximate with finite element/boundary element method. The theoretical prediction is compared with the observation data of Xingtai earthquake 1966, Hejian earthquake 1967, Tangshan-Luanxian earthquake 1976 and Wenchuan earthquake 2008. Keywords Fault, Strong Earthquake, Block and Plate, Instability, Fracture theory 1. Introduction In China, some strong earthquakes happened in plate rather than in boundary between plates. These strong earthquakes are called in plate strong earthquake, or land strong earthquakes. The typical examples are the Ms7.3 Xingtai earthquake on March 8, 1966, the Ms7.8 Tangshan earthquake on July 28, 1976, the Ms8.0 Wenchuang earthquake on May 8, 2008, etc., which resulted in serious destroy and killed a lot of people. Why did the strong earthquakes happen in plate? To explain the phenomenon, geologists, geophysicists and seismologists in China put forward the block hypothesis of the land strong earthquakes [1-5]. They observed that these earthquakes appeared in the boundaries between blocks. In China land the blocks are very developed, some blocks have quite big sizes though they are smaller compared with plates. For example, the Wenchuang earthquake is in Wenchuang-Beichuang fault, which is located in the boundary between the Tibet Block and the South China Block that have huge sizes. The land strong earthquake presents some natures themselves different from those of earthquakes in boundary between plates. In this work, we focus on the block characters and apply fracture theory doing some analysis, and preliminarily explain phenomena concerning Xingtai Earthquake, Tangshan earthquake and Wenchuang earthquake those happening in China land. 2. Physics modeling The land strong earthquakes occurred along some faults in the boundary between blocks, a crack
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