郯庐断裂带中段重力场变化及地震活动特征

Characteristics of the gravity change and the recent seismic activity of the middle part of Tancheng-Lujiang fault zone

基于郯庐断裂带中段区域网的地震资料及山东、辽宁区域的重力资料，研究了近期该区内主要小震活动与活动断裂、应力场及重力场的相互关系.结果表明：（1）该区域小震活动主要集中于5~10 km深度，分布于近NW和NWW的断裂上，而NNE向的郯庐断裂带鲜有小震发生，最大主压应力轴优势方位为 80左右，主要为NE、NEE或近EW向，与郯庐断裂走向近乎垂直，在这种挤压应力场的作用下，会增强NNE断层两侧的应变积累，不易使其产生错动，但有利于NW向和 NWW向断层的活动.（2）小震活动主要分布于重力0等值线附近，断裂带两侧的密度差异容易诱发地震.（3）重力场的变化与Pn波速度结构比较吻合，负重力变化区域与Pn波低速异常区有一定的关系，推测其原因可能是对壳内温度升高、物质膨胀、密度发生变化的反映.

Based on seismic data recorded by digital seismic network in the middle part of Tancheng-Lujiang Fault zone and regional gravity data of ShanDong and LiaoNing, the relations between the recent seismic activity and stress field, active fault, gravity field are studied. The result shows d the following features：In this region,small earthquakes are mainly concentrated 5~15 km and distributed near the NW and NWW striking fault, the NEE striking Tancheng-Lujiang fault is almost no small earthquakes activity,the predominant distribution direction of Principal compressive stress is about 80o, the direction are main NE, NEE or nearly EW, the nearly horizontal NEE-SWW striking principal compressive stress is in favor of the strain accumulation of NNE striking faults and NW and NWW striking faults moving （2） small earthquakes are mainly distributed on the 0 value contour line of gravity, the density differences of the fault both sides are easy to cause earthquakes. （3） the gravity changes are more consistent with Pn velocity, the negative gravity change may reflects the local uplift of deep crust-mantle and the which has a certain correlation with the low Pn velocity anomaly region.