山西地区远震P波到时残差分布

收集2008—2016年山西地震台网记录的震中距30°—90°范围内1 253个远震事件波形,拾取7 600余条高质量P波初至到时,使用IASP91模型计算相对到时残差,分析残差水平分布特征,结果显示:①以山西地区中部的山西断裂带为界,西部地震台站记录的P波初至主要表现为早到时,东部位于大同火山区的地震台站记录则主要表现为晚到时;②位于山西断裂带内部的地震台站记录的P波初至主要表现为早到时,残差水平显著低于西部地震台站;③研究区P波到时整体呈现自西向东逐渐由早到晚的分布特征。推测山西断裂带西部地区下方可能存在高速异常结构,山西断裂带内部及大同火山区下方可能存在低速异常结构。

The tectonic significance of the P wave travel-time residual variation of teleseism in Shanxi region

The geologic structure is very complex and the seismicity is highly frequent in Shanxi Province. In this study, the teleseismic data from 2008 to 2016 (central distance: 30-90 degree) have collected. More than 7 600 high quality arrival times are manually picked from 481 seismic events recorded by 21 digital seismic stations. After the analyses and calculation of relative residuals, it is found that the stations in the Datong volcanic region show delayed arrivals, while those in the west of Shanxi fault exhibit obvious earlier arrivals. The stations along the Shanxi rift zone show relative residuals early arrivals, but they are much smaller. These results suggest that there are low-velocity anomaly layer under the Shanxi rift zone, quite similar to the Baikal rift zone. In particular, there are obvious low-velocity anomalies under the Datong volcano, which indicates that the Datong volcano maybe relate to the deep dehydration of the stagnant pacific slab in the mantle transition zone.