中国大陆地应变率场分布及其与地震活动性关系的研究

A study on the relationship between GPS­ground strain rate field and seismicity in the Chinese mainland

摘要:

利用中国大陆地区的GPS速度观测资料，通过2次插值计算，得到地应变率场。首先将GPS观测结果通过插值计算获得中国大陆及邻区均匀网格节点上的速度值，然后运用有限单元中形函数(Lagrange插值函数)的求导方法，计算每个网格单元积分点处的地应变率分量，从而获得中国大陆及邻区稳定的地应变率场的分布。计算结果表明，总体上中国大陆及邻区地应变率分布西高东低；以南北地震带为界，西部地区应变率高，而东部地区，尤其是华南地区地应变率很低；而塔里木盆地、鄂尔多斯盆地等构造稳定区域的地应变率也很小。此外，还发现中国大陆及邻区地应变率分布与地震活动之间的关系非常密切，变形产生的应变能密度与地震密度(1.0°×1.0°内发生的地震数目)之间吻合得很好，应变能密度高的区域，地震活动性较强；反之，则较弱。同时，最大剪应变率、面应变率与地震活动性之间也呈对应关系。

Abstract:

An earthquake is a mechanical process in which elastic strain energy is released suddenly once stresses in the focal region are accumulated to a critical extent. Therefore，there exists an intrinsic connection(http://cn.bing.comdictsearch？q＝.&FORM＝BDVSP6) between the process of earthquake preparation and the cumulation of crustal strain. In this paper，strain rate field is calculated by the use of GPS velocities observed in the Chinese mainland with twice interpolations approach. Interpolating the scattered GPS velocity data of Chinese mainland and its adjacent areas to grid point values by Kriging，we then calculate the strain rate from these nodal values of each element similar to derivative of shape functions(essential Lagrange interpolation function)in finite element algorithm，and obtain the stable distribution of strain rate field in the studied area. The results show that the strain rates in China and its adjacent areas on the whole are high in the west and low in the east. The strain rates are evidently larger in the western region of China than those in the east bounded by North-South Seismic Belt. To the east of the belt，strain rates are very low，especially in southern China. In addition，the tectonic stable regions such as the Tarim Basin and Ordos Basin show low strain rates. Moreover，the calculated results suggest that the seismic activity is closely related to the strain rates in China and its adjacent areas. There is a very close relationship between strain energy density and seismicity. Where strain energy is large，seismicity is high，and vice versa. We also found correspondences between seismicity and the maximum shear strain rate and surface strain rate. Therefore，the calculation of strain rate field will provide an important reference for seismic hazard assessment.