汶川M8.0地震前后山西地震带水平形变场变化特征研究

Characteristics of Horizontal Deformation Field of the Shanxi Seismic Zone before and after the Wenchuan M8.0 Earthquake

摘要:

通过分析汶川M8.0地震前后山西地震带GPS速度场以及由此计算得到的现今构造应变率场，结果显示：（1）汶川M8.0地震后，山西地震带各区域的运动方向均不同程度向西偏转，太原盆地及其以北的区域由1999—2007年的SW或SSW向转为SWW向，且运动速率由平均约2 mm/a增加到约4 mm/a，太原盆地以南的区域由之前的SSE向转为SW向。（2）汶川M8.0地震后，山西地震带的应变率场显著增强，大同盆地、太原盆地北段和临汾盆地西南段形成了三个压性应变集中区，2010年在这三个区域内分别发生了大同M4.5、阳曲M4.6和河津M4.8地震，可能由于这种压性应变积累的区域应力场环境有利于山西地震带中强地震的孕育和发生。（3）2009—11年，受日本M9.0地震的影响，山西地震带向西运动的速率有所减弱，应变率场张性变化明显，太原盆地及其以北区域平均速率下降为约2~3 mm/a，太原盆地以南的区域由SW向转为整体向南运动的格局，有恢复到1999—2007年背景运动状态的迹象。

Abstract:

We obtain the horizontal velocity field and tectonic strain rate field of the Shanxi seismic zone derived from Global Positioning System（GPS） data before and after the Wenchuan M8.0 earthquake.The results indicate that after the Wenchuan M8.0 earthquake，the velocity of each region in the Shanxi seismic zone deflected westward in varying degrees.The north area including Taiyuan Basin shifted to SWW from SW and SSW directions in 1999-2007，and the velocity developed from an average of approximately 2 mm/a to 4 mm/a. In addition，the area south of Taiyuan Basin shifted to SW from a SSE direction.The strain rate field in the Shanxi seismic zone was significantly enhanced after this earthquake and formed three compressive strain concentration areas in Datong Basin，north Taiyuan Basin，and southwest Linfen Basin.In these respective areas, the Datong M4.5，Yangqu M4.6，and Hejin M4.8 earthquakes occurred in 2010.These earthquakes may have occurred because a regional stress field environment with compressive strain accumulation is beneficial to the formation and occurrence of a moderate earthquake in the Shanxi seismic zone.Moreover，because of the Japan M9.0 earthquake，the westward velocity of the Shanxi seismic zone was weakened，and the strain rate field expanded obviously during 2009 to 2011.In addition, the velocity in the north area including Taiyuan Basin decreased to approximately 2~3 mm/a，and the area south of Taiyuan Basin moved toward the south from the SW direction.This area may return to the background velocity of that during 1999 to 2007 in the future.