利用P波“影区”特征探测青藏高原东部岩石层内低速层  

Exploration of the low-velocity layer within the lithosphere beneath the eastern Qinghai-Xizang Plateau using the P wave shadow zone

作　　者：焦煜媛 沈旭章[1,2] 马克博 钱银苹 王静波[1] Jiao Yuyuan Shen Xuzhang Ma Kebo Qian Yinping Wang Jingbo(Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China Lanzhou Base of Institute of Earthquake Science, China Earthquake Administration, Lanzhou 730000, China)

机构地区：[1]中国地震局兰州地震研究所,中国兰州730000 [2]中国地震局地震预测研究所兰州科技创新基地,中国兰州730000

出　　处：《地震学报》2016年第6期824-834,共11页Acta Seismologica Sinica

基　　金：中国地震局地震预测研究所基本科研业务专项(2014IESLZ03);国家自然科学基金(41274093;41574077)共同资助

摘　　要：选用我国西藏及其周边地区测震台网35个台站宽频带数字地震仪记录到的2014年10月7日云南普洱MS6.1地震的波形资料,分析了垂直向分量初至P波的幅度特征.结果表明:在震中距处于5°—18°之间的P波初动幅度相对较小,存在"影区"特征,推测该"影区"是由青藏高原下方岩石层内低速层所引起的;通过试错法,多次对比不同模型的理论波形与观测波形的P波初动振幅随震中距的变化形态,最终确定在78km深处存在一厚度为24km的低速层,层内速度梯度约为-0.05/s.This paper analyzed the first arrivals of vertical P waveforms of the Pu＇er MS6.1earthquake in Yunnan Province on October 7,2014 recorded by 35 broadband digital seismic instruments that belong to seismic networks of Xizang（Tibet）and its surrounding areas.The result shows that amplitudes of P wave onsets are relatively weak in the epicentral distance of 5°—18°,which is consistent with the characteristics of shadow zone.Therefore,it is deduced that the low-velocity layer within lithosphere beneath the Qinghai-Xizang Plateau might be the most possible reason for the shadow zone.Based on the numerical testsof trial and error method and comparison of the observed amplitudes with synthetic ones of P wave onsets predicted by the reflectivity method,the model with a low-velocity layer of 24 km thick at the depth about 78 km can well explain the observations,and the velocity gradient within the low-velocity layer is-0.05/s.

关 键 词：岩石层 低速层 地震波影区 理论地震图 青藏高原 

分 类 号：P315.63[天文地球—地震学]