陕西地区小微震震源机制研究

Research on Focal Mechanisms of the Small and Micro Earthquakes in Shaanxi Area

小微震事件的震源机制是区域应力场及诸多地球动力学研究的基础资料。陕西地区为多个地震带的交汇区,近些年积累了丰富的小微震波形资料。运用新近发展的适用于求解小微震震源机制的广义极性振幅技术(GPAT),结合陕西2015地壳速度模型,求解陕西测震台网2011年4月至2015年12月间记录的121次ML1.5~3.5事件的震源机制。反演结果表明:(1)以上事件的震源机制大部分为走滑及正断类型,其比例占64.5%;逆断型机制占22.3%。(2)反演震源机制得到的震源深度与定位深度具有良好的一致性;矩震级与近震震级间存在差别,且这种差别随事件的变小而增大。(3)对比渭河断陷带相关研究成果,验证了该区域震源机制以正断型为主,具有拉张应力状态。

Focal mechanisms of small and micro earthquakes are used as basic data for studies on regional stress fields and for other geodynamics studies. The Shaanxi region is at the intersection of several seismic zones, and abundant waveform data of small to microseismic events have been accumulated in recent years. This study uses the recently developed generalized polarity and am plitude technique （GPAT）, together with a 2015 crustal velocity model of Shaanxi, to invert the focal mechanisms of 121 small and micro earthquakes with a range between ML1.5 and ML3.5 that occurred between April, 2011 and December, 2015, that were recorded by the seismic net work of Shaanxi. Inversion results show that focal mechanisms of these events were mostly strike slip and normal fault types （64.5%） and thrust faulting types （22.3%）. In addition, there is a good consistency between the focal depth inverted from the focal mechanism and the location depth. However, there is a difference between the moment magnitude and local magnitude, and this difference increases with a decrease in magnitude. Furthermore, compared with other study results conducted within the Weihe fault zone, this study verifies that normal fault types mainly control the focal mechanisms of earthquakes, and they are in a state of tensile stress.