由现今小震资料研究琼北地区区域应力场和发震构造

利用2000年以来海南地震台网记录的琼北地区的波形资料,采用双差法对103个地震进行重新定位,采用振幅比方法测定震源机制.在此基础上,反演了琼北地区的区域应力场,由震源位置拟合出两个震源断层面,并且计算在区域应力场作用下的滑动方式.对照历史大震的等震线,WNW走向的震源断层位于极震区中部稍偏东的地方,与等震线长轴方向相同,表明该震源断层是1605年琼山大震的发震构造;高倾角震源断层的北东盘向东南斜下方滑动,对于该盘NNW象限产生强烈拉张,以致出现罕见的陆陷成海现象.另外一条NS向震源断层恰好位于第四系火山岩和第四系盆地交界处,是区域升降运动最为强烈的地方,正断层类型的震源断层东盘下降,与沉积盆地一致.研究表明由现今小震反演的两条震源断层分别与历史大震及构造运动有关,而与浅表断裂并不重合,存在深浅构造不协调的现象.

The stress field and seismogenic structure in northern Hainan island based on current small earthquakes

Based on the seismic waveforms recorded by Hainan seismic network in the northern Hainan island since 2000,103 earthquakes were relocated by double-difference method and some focal mechanisms were determined by amplitude ratio. We inverted the regional stress field from the focal mechanism and two focal fault planes from the precise hypocenters, and inferred the slip type of the focal fault under the regional stress field. Contrasting with the isoseismal line of the historical earthquake,the WNW focal fault located in the eastern central part of the meizoseismal area, which has the same direction as the major axis of the meizoseismal area.This indicates the focal fault may be the seismogenic structure of Qiongshan earthquake in 1605. The northeast wall of the high angle focal fault slipped down to southeast, which makes the NNW quadrant extensional and leads to the land subsidence into the sea. Another NS focal fault just located on the boundary between the Quaternaryvolcanic rocks and Quaternary basin where the lifting movement is the most intense.The eastern wall of the normal focal fault dropped, which was consistent with the sedimentary basin. The results show that this two focal faults are related to the historical earthquake and tectonic movement,but do not coincide with the surface fault, indicating an uncoordinated phenomenon between the shallow and deep tectonics.