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Effect of source parameters on forward-directivity velocity pulse for vertical strike slip fault in half space

Liu Qifang (刘启方)1, Yuan Yifan (袁一凡)1 and Jin Xing (金 星)1,2

1. Institute of Engineering Mechanics, China Earthquake Administration, Harbin 150080, China

2. Earthquake Administration of Fujian Province, Fuzhou 350003, China

Abstract: It has been found that the large velocity pulse is one of the most important characteristics of near-fault strong ground motions. Some statistical relationships between pulse period and the moment magnitude for near-fault strong ground motions have been established by Somerville (1998); Alavi and Krawinkler ( 2000); and Mavroeidis and Papageorgiou ( 2003), where no variety of rupture velocity, fault depth, and fault distance, etc. were considered. Since near-fault ground motions are significantly influenced by the rupture process and source parameters, the effects of some source parameters on the amplitude and the period of a forward-directivity velocity pulse in a half space are analyzed by the finite difference method combined with the kinematic source model in this paper. The study shows that the rupture velocity, fault depth, position of the initial rupture point and distribution of asperities are the most important parameters to the velocity pulse. Generally, the pulse period decreases and the pulse amplitude increases as the rupture velocity increases for shallow crustal earthquakes. In a definite region besides the fault trace, the pulse period increases as the fault depth increases. For a uniform strike slip fault, rupture initiating from one end of a fault and propagating to the other always generates a higher pulse amplitude and longer pulse period than in other cases.

Keywords: forward-directivity velocity pulse; amplitude; pulse period; source parameters; rupture velocity; fault depth; asperity