2012年以来新疆于田强震前震序列的时空演化模式

巴颜喀拉块体边界地震活跃, 其西边界新疆于田地区在2008年发生M7.3地震后, 2012年以来又陆续发生了M6.3、M7.3和M6.4三次强震.然而该地区的地震监测台网非常稀疏, 地震目录的完备性低, 定位精度差.为了研究于田区域的前震活动规律, 本文利用单台波形模板匹配方法重新检测了2011年6月以来的连续波形, 改善地震目录, 并用单台定位约束地震的相对位置.结果获得新的地震数量是台网目录的15倍, 完备震级从原来的2.8降为1.3, 更有利于前震序列时空演化特征的回溯研究.研究区地震b值在三次强震前都表现出持续降低, 在临震前回弹, 主震后恢复.在空间上, 前震活动往往有两个阶段, 早期活动先是分散在硝尔库勒盆地周缘, 临震前成簇聚集到主震附近, 有断层级联破裂的特征.特别是2014年M7.3地震, 大量的前震出现在主震南侧并向北迁移和停滞, 它们的波形相似性很高, 反映出临震前的构造应力集中和地震成核.

The foreshock temporal-spatial evolutionary patterns of the strong earthquakes since 2012 in Yutian,Xinjiang, China

Recent seismicity along the boundary of the Bayan Har block has been quite active. At its western, the Yutian area has successively occurred three strong earthquakes with magnitudes of 6.3, 7.3, and 6.4 since 2012, just after an M7.3 earthquake in 2008. However, the seismic network in this area is very sparse, the earthquakes are poorly located, and many are undetected in the catalog. To further investigate the foreshock pattern in this region, we performed matched filter detection over the continuous waveforms in a single seismic station after June 2011 and relatively located these detected earthquakes with the single station method. As a result, the number of the newly detected earthquake is 15 times higher than that of the CENC catalog, and the completeness magnitude is dropped from the original 2.8 to 1.3, which is more favorable for the retrospective study of the spatial-temporal evolution of the foreshock sequences. The b-values in the study area showed a continuous decrease several months before and rebounded at the impending of the mainshocks, then recovered after the mainshocks. The foreshock spatial migration patterns usually have two stages, which generally scatter around the margin of the Xiaoerkule basin at the early stage and then cluster near the mainshock at the impending stage, exhibiting the characteristic of fault cascade rupture. Especially in the 2014 M7.3 earthquake, a large number of foreshocks appeared on the south side of the mainshock with very similar waveforms, migrated and stagnated northward, reflecting the tectonic stress concentration and earthquake nucleation before the mainshock.