关键词: 黏弹性, 三维有限元, 活动断裂, 应力场, 强震预测

Abstract: The seismogenic factors of the physical model for strong earthquake generation in North China established from the results of geophysical exploration are numerically analyzed by using the 3-D finite element method for visco elastic medium with split node. The results demonstrate that an area of stress accumulation will exist when fault activity occurs around the low-velocity body. In addition, the distribution of slip rates at depth for the major active faults in Capital Circle are inversed from GPS measurement data. Fault slip rate is usually about 10mm/a in this region, and it is higher for the faults in the western part than in eastern part of the region. Moreover, the slip rates of buried deep faults are higher than those of the shallow faults. These slip rates are treated as inner boundary conditions for the 3-D visco elastic finite element calculation. Then the variation of stress field and energy distribution with time in Capital Circle are simulated by considering a geologic body of 50km depth, 300km length and 220km width, with compressive stress of -9MPa in East West direction and -3MPa in North South direction, regardless of gravity. The distributions of initial effective stress and strain energy density are influenced mainly by the inhomogeneity of medium, especially the low-velocity body. Faulting process may cause the variation of effective stress and strain energy density. The variation rates of effective stress and strain energy density for each element can be obtained through several steps of visco elastic calculation. According to the physical structure of strong earthquake generation, the distribution of initial stress field and the increment of additional stress field, we have determined 3 potential risk areas of strong earthquake. They are the Yan Huai Basin, the Southeast margin of Yangyuan Basin and the Daxing Zhuozhou area. Moreover, the maximum potential earthquakes for these 3 risk areas are estimated to be M7, M6.5 and M6, respectively on the basis of different accumulation rates of strain energy, the volumes of seismic source bodies, and the Gutenberg-Rithter relation. As compared with historic earthquakes in these areas, the current accumulation rate of strain energy in Yan Huai Basin coincides well with that for the recurrence of historic earthquakes, but the coincidence is not good for the Southeast margin of Yangyuan Basin and the Daxing Zhuozhou area.

Key words: visco elasticity, 3-D FEM, active fault, stress field, prediction of strong earthquake