2015年9月14日在河北昌黎发生了M_S4.2地震，这次地震位于唐山老震区，是2015年内首都圈地区最显著的地震。本文计算了这次地震的地震矩张量和2015年内发生在其附近小地震的震源物理参数，对比之前的研究成果讨论了小区域的应力状态。以往应力场研究侧重于最大应力主轴方向，本研究通过计算地震视应力参数估计了区域绝对应力水平下限，获得了有关应力状态的丰富信息。本文采用①反演地震矩张量的波形拟合法及②积分宽频带平均震源谱法2种方法计算出地震矩，得到的地震矩比较接近，说明本文计算流程和参数选择合理。综合分析得出下面两点认识：①区域应力场受到华北应力场控制，同时也表现出小区域特征；②地震视应力分布与10年前相比没有明显差别，可能意味着该区域的地震活动会维持现状。

A M_S4.2 earthquake occurred on August 14,2015 in Changli,Hebei. Its location was close to that of the 1976 Tangshan earthquake,and it's the largest earthquake in 2015 in the Capital Region. This paper calculated the moment tensor solution of this earthquake and apparent stresses of small earthquakes in 2015 in the nearby region. We discussed regional crust stress by using these calculations. Most previous researches study the azimuth of principal axis. Here we showed information of absolute stress value of earth crust by using earthquake apparent stress. We calculated seismic moment using 2 methods:① inversion of moment tensor by fitting theory seismograms and observed ones,② integration of broad band average seismic spectrum. The seismic moment calculated from these 2 methods are similar,and demonstrates the validation of these 2 methods. We conclude that:① the stress field of earth crust in study area is coincidence to that in the Northern China,but it also shows regional characteristics,② the distribution of earthquake apparent stress is similar to those in the past 10 years which implies that the future seismicity remains unchanged.

P315

国家自然科学基金（41274062）资助