利用小震分布和区域应力场确定大震断层面参数方法及其在唐山地震序列中的应用

An algorithm of fault parameter determination using distribution of small earthquakes and parameters of regional stress field and its application to Tangshan earthquake sequence

根据成丛小震发生在大震断层面及其附近的原则,将模拟退火算法和高斯-牛顿算法结合,给出了利用小震密集程度求解主震断层面走向、倾角、位置及其误差的稳健估计方法,在此基础上考虑区域构造应力参数,给出了估计在已求得的断层面上的滑动角的方法.该方法还可用于小震活跃地区活断层走向、倾角和滑动角的确定.将这种方法用于唐山地震序列,采用2002年4月1日至2006年5月31日发生在地震破裂区的精定位地震目录,求得了唐山地震、滦县地震、宁河及卢龙断裂带的断层面走向、倾角、位置及滑动角参数.与前人给出的断层面解进行比较,发现利用小震精定位资料和区域构造应力场得到的结果与前人采用其他资料和方法得到的结果近似,验证了这种方法的有效性.另外,本研究首次发现滦县地震区东部的小震呈北东-南西向条带状成丛发生,可精确刻画为一条断裂带,较为精确地确定了此断层的走向、倾角和滑动角.该断裂及宁河断裂在唐山地震序列发生时是否破裂需要运用其他资料进行验证.

It is known that clustered small earthquakes often occur in the fault plane vicinities of large earthquakes. Based on the simulated annealing and Gauss-Newtonian nonlinear inversion algorithms, we develop a robust algorithm to estimate fault plane parameters of strong earthquakes such as strike, dip, and location using data of densely populated small events. Rake angle of the fault plane is further inferred from regional tectonic stress parameters. This method can also be employed for determination fault plane parameters of an active fault using data of densely populated small earthquakes. We apply the algorithm to investigate the fault planes of the 1976 Tangshan, Luanxian, and Ninghe earthquakes and the Lulong fault, using precisely relocated earthquakes which occurred near the earthquake rupture zone between 1 April 2002 and 31 May 2006, and obtain the parameters of strike, dip, location, and rake angle of these fault planes. Our estimated fault planes are close to the results of previous studies, testing the validity of our method. In addition, we discover an aligned seismic belt east of the Luanxian seismic zone trending NE-SW, in the form a fracture zone. The faulting parameters of the fracture zone such as the strike, dip and rake are determined accurately. It is still an open question whether the Luanxian and Ninghe faults have ruptured during the Tangshan earthquake sequence, answers to the question await for further multi-disciplinary studies and bear great significance for the understanding of dynamic processes of the Tangshan earthquake sequence.