青海玛多MS7.4地震前b值时空变化特征

大量研究表明地震孕育过程中存在相对平静期，该阶段b值会相对下降，b值变化在地震活动性研究中起着十分重要的作用。2021年5月22日青海玛多发生MS7.4地震，为研究地震前b值时空变化特征，本文截取2009年至震前地震目录，将地震目录分为去除余震目录、完整地震目录，对比研究b值变化特征。研究发现，玛多MS7.4地震前1年b值开始低于均值且不断下降，至b值有上升趋势时地震发生，扩大到区域内其它5级以上地震，也符合此规律，地震发生后b值明显上升，短时间内又下降至较低位置，并一直处于较低位置直至下次地震发生；从b值空间扫描结果看，玛多MS7.4地震前，震中位于低b值区域，该位置为b值最低处；通过不同时间段的b值空间扫描结果，可发现玛多MS7.4地震发生前低b值区域向震中不断迁移，表明地震发生前震中附近应力不断集中；b值空间扫描时，完整地震目录掩盖了中强震震中区域低b值特性，去余震地震目录较好的凸显了中强震震中区域低b值特性。

Temporal and Spatial Variation of b-value before Maduo MS7.4 Earthquake

A large number of studies have shown that there is a corresponding quiet period in the gestation process of an earthquake, during which the b-value will decrease accordingly, and the change of b-value plays a very important role in the study of seismic activity. M_S7.4 earthquakes occurred in Maduo County, Qinghai Province on May 22, 2021. To study the relationship between the spatiotemporal changes of b-value before the earthquake, the earthquake catalog from 2009 to before the earthquakesis extracted to study the changes of b-value in the earthquake focal area. The results show that the b-values of this earthquake in the focal area of earthquake with a magnitude of more than 5 decreased correspondingly about half a year before the earthquake, while the b-value rises suddenly and then decreases rapidly before the earthquake, and the earthquake mostly occurs in the descending stage. In this paper, short-term spatiotemporal scanning was carried out for two earthquakes above M5 in the focal area, and the epicenters were all located in low b-value region. This study found that short-term changes in b-values seem to be related to earthquakes. The epicenters of moderate and strong earthquakes in the study area are all located in low b-value areas. Further research is needed to determine whether this feature is universal or not, and ultimately to find the best earthquake prediction method.