九江-瑞昌地震震源机制和应力场特征

利用九江-瑞昌5.7级地震后震区地震波形资料，采用Snoke发展的基于P波、SV波、SH波初动和振幅比联合计算震源机制解的方法(FOCMEC)，分两个时段反演得到176个ML≥1.0地震的震源机制解。结果显示，MS5.7主震发震断层是在近EW向的区域应力场挤压作用下产生的带有逆断性质的左旋走滑断层，余震也以走滑型运动为主，NW向洋鸡山-武山-通江岭隐伏断裂为主震的发震构造。地震节面走向主要集中在NEE和NWW两个方向，与余震分布优势方向、震区构造大体一致。两个时段的震源机制解P轴优势方向均为近EW向，与主震P轴方向接近，也与江西北部地区的构造应力场分布特征相一致。应力场反演结果与震源机制参数统计结果整体一致，表现为近EW向挤压和近NS向拉张作用。

Characteristics of Focal Mechanisms and Stress Field in the Border Region of Jiujiang and Ruichang

Using the latest method developed by Snoke for calculating focal mechanism solutions using the combination of P wave, SV wave and SH wave (FOCMEC), we inversed the focal mechanism solutions of 176 ML≥1.0 earthquakes of two times after Jiujiang-Ruichang MS5.7 earthquake. The results show that the seismogenic fault of the mainshock MS5.7 is a sinistral strike slip fault with thrust property under the extrusion of the near EW direction stress field, with most aftershocks presenting a strike slip motion. The NW Yangjishan-Wushan-Tongjiangling buried fault forms the seismogenic structure of the main shock. The predominant strike direction of nodal planes are NEE and NWW, which is largely consistent with the predominant direction of aftershock distributions and tectonic strikes. The dominant direction of the P axis of focal mechanism solutions is nearly EW, close to the direction of P axis the main shock. It is also consistent with the distribution of tectonic stress field in northern Jiangxi. The inversion results of the whole stress field are consistent with the statistical results of the focal mechanism parameters, which show the effect of the near EW direction extrusion and the near NS tension.