福建仙游震群的应力场及其成因分析

Analysis of stress field and its causes of the Xianyou earthquake swarm in Fujian

利用双差定位法对2010年8月1日至2014年12月31日福建仙游地区中国地震台网中心记录到的地震群进行重定位,并采用P波初动的方法求解出该震群的159个震源机制解,显示该震群的震源机制解结果与背景构造应力场表现明显不一致。为了进一步探究差异性存在的原因,将得到的震群震源机制解结果分区域和分深度求解应力场,结果显示:金钟水库的东南部附近应力方向更远离背景构造应力方向,并且应力形因子小于0.5,中间轴呈现为拉张应力;随着深度的增加,应力场的方向也更接近背景构造应力场的方向。此外,根据前人研究推断该区域应力方向发生偏转是由于太平洋板块在深部的低角度俯冲挤压导致浅部张开,应力呈现为东西向拉张所致。在上述两原因的共同作用下,使得经震源机制解反演出的应力场结果与背景应力场差别较大。

This study employed the double-difference location method to relocate earthquakes recorded by the seismic network center in the Xianyou region of Fujian from August 1,2010,to December 31,2014.It also used the initial motion of P waves to determine the focal mechanism solutions for 159 events within this seismic cluster.The results reveal a significant inconsistency between the focal mechanism solutions of the cluster and the background tectonic stress field.To further investigate the reasons behind this discrepancy,the obtained focal mechanism solutions were analyzed to calculate the stress field by region and depth.The findings indicate that in the southeastern part,near the Jinzhong Reservoir,the direction of stress deviates more from the background tectonic stress direction,with a stress shape factor less than 0.5,and the intermediate axis showing extensional stress.As depth increases,the direction of the stress field also becomes closer to that of the background tectonic stress field.Additionally,based on previous research,it is inferred that the deviation in stress direction in this area is due to the lowangle subduction and compression of the Pacific Plate at depth,leading to extension at shallow levels,with the stress manifesting as east-west extension.Under the combined influence of these two factors,the stress field results deduced from the focal mechanism solutions differ significantly from the background stress field.