利用近震Sp转换波到时和远震接收函数P波峰值延迟研究华北盆地浅部结构

Research the shallow structure of the Northern China Basin using near earthquake Sp converted waves and teleseismic P wave delay

收集2017—2020年中国地震科学探测台阵在华北地区布设观测宽频带流动地震观测台采集的高信噪比近震远震地震波形,采用远震接收函数P波峰值延迟和近震Sp转换波到时对华北沉积层厚度进行了估算.由远震接收函数P波峰值延迟,近震Sp转换波和S波到时差方法推断的华北地区沉积层厚度在6~7 km,燕山造山带区域沉积层厚度较小,结晶基底埋深一般小于1 km,华北盆地中部和东南部盆地结晶基底埋深较厚,厚度普遍大于3 km,局部厚度可达7 km.盆地内地垒式隆起区邢衡隆起有3 km厚度的沉积层,冀中坳陷、黄骅坳陷厚度6~7 km;沉积层厚度与地质构造相对应,坳陷区沉积层厚度较大,隆起区沉积层厚度较小,体现了沉积盆地内部不同二级块体的沉降差异.震相拾取误差、震源方位角和震中距对沉积厚度计算结果影响不明显;进行时深转换采用的一维速度模型准确性对计算结果存在一定影响.总体来说,远震接收函数P波峰值延迟和近震Sp转换波到时可以研究沉积层厚度,能够可靠、有效地确定沉积层厚度结构的特征,为地震风险评估提供基础信息.

We collected the local shock seismic waveforms and teleseismic waveforms with high signal-to-noise ratio which recorded by broadband seismic observatories deployed in Northern China from 2017 to 2020.The thickness of the sedimentary layer in Northern China is estimated to be 6~7 km by using teleseismic receiver function P-wave peak delay and local shock Sp converted wave time delay.The thickness of the sedimentary layer in the Yanshan orogenic belt is relatively thin,with a burial depth of crystal basement generally less than 1 km.The burial depth of crystal basement in the central and southeastern basins of Northern China Basin is relatively large,with a thickness generally greater than 3 km,and local thickness up to 7 km.The Xingheng uplift in the basin has 3 km thickness sedimentary layer,while the Jizhong and Huanghua depressions have a thickness of 6~7 km;The thickness of the sedimentary layer corresponds to the tectonics.The thickness of the sedimentary layer in the depression area is larger,and the thickness of the sedimentary layer in the uplift area is thin,which reflects the settlement difference of different secondary blocks in the sedimentary basin.The seismic phase picking error,source azimuth and Epicentral distance have no obvious influence on the sediment thickness calculation results,while the accuracy of the one-dimensional velocity model used for time depth conversion has a certain impact on the calculation results.In general,teleseismic receiver function P-wave peak delay and local shock Sp converted wave time delay can be used to study the thickness of sedimentary layers,and it can determine the characteristics of the thickness structure of sedimentary layers reliably and effectively,providing basic information for seismic risk assessment.