中国构造应力场与大震复发周期关系的数值模拟

TECTONIC STRESS FIELD AND LARGE EARTHQUAKE RECURRENCE PERIOD IN CHINA

由古地震资料推算得到的中国境内各活动断裂带上大震复发周期值存在很大差异，对于这种差异可从构造应力产生的弹性应变能分布去探讨其原因。经过对中国及邻区边界条件和受力方式进行较详细的分析后，先以最大主压应力方向为判据，用有限元数值模拟方法反演中国及邻区的板块边界力和区内的构造应力场，然后分析计算应变能随离板块边界的距离增大所呈现的衰减规律，由此换算出要达到相同应变能（一次地震）各地所需的积累时间，并将其与用古地震方法得到的一些已知断层带大震复发周期进行对比。结果表明用应力衰减图象能解释不同地区大震复发周期的显著差异。

The recurrence interval of large earthquake varies from one active fault to another inferred from palaeoseismic data in China. Generally speaking, the interval in eastern part of China is much longer than that in the western part, and that around the plate boundary is remarkably shorter than within the plate of China. To consider the reason for the phenomenon, a mechanical model was constructed by the method of finite element numerical analysis to probe into the distribution of elastic strain energy caused by tectonic stress. The procedures to be used in this paper are: (1) to analyze the boundary condition and action pattern of force on the boundary in China and its adjacent areas by geological method, (2) to make inversion of the force acted on the boundary and the tectonic stress field in the region by finite element method based on the criterion of the maximum principal stress direction, (3) to calculate the attenuation of strain energy with the increase of distance apart from the plate boundary. Based on the attenuation pattern, the accumulative range of strain energy is converted to reach a given value (a given magnitude of large earthquake) in different parts of the research region into time or period, which is compared with the known recurrence interval of large earthquakes along an active fault zone obtained by palaeoseismic method. The comparison shows that the remarkable difference of large earthquake recurrence intervals between plate boundary and plate interior can be well explained by the attenuation pattern of strain energy.