利用背景噪声和接收函数研究华北克拉通地壳结构

Crustal structure beneath the North China Craton from joint inversion of ambient noise and receiver function

收集华北克拉通地区188个宽频带流动台站观测资料进行处理.通过背景噪声面波数据和接收函数双重资料约束联合反演,得到了研究区沉积层厚度、地壳厚度及地壳S波速度结构.结果显示:(1)沉积盖层厚度与地质构造相对应,盆地区与隆起区分界明显.(2)研究区地壳厚度变化范围约29~46 km,自西向东逐渐变薄.(3)中、上地壳华北盆地S波速度偏高,可能与新生代以来多次沉降所造成的相对高的岩石强度有关;(4)下地壳S波速度显示研究区主要存在三个低速区,分别是唐山—天津周边、张北及太行山造山带地区;华北盆地存在显著高速异常,推测可能是由于华北盆地经历下地壳拆沉后,大规模的伸展作用相伴随的幔源基性铁镁质岩浆底侵至下地壳结晶所造成的.(5)多个发生过强震的区域表现出沉积层下方存在较大范围的(约10 km)高速体,并且高速体又被其下低S波速度包裹,壳内岩石强度的差异为应力积累及地震发生提供条件.

We collected waveforms from 188 broadband seismic stations deployed in the North China Craton(NCC).Based on these data,we obtained the sediment thickness,crustal thickness,and S-wave velocity structure of the crust in the study area through the joint inversion of ambient noise surface wave data and receiver function data.The results demonstrate:(1)The sediment thickness corresponds to the geological structure.(2)The crustal thickness changes from 29 km to 46 km,thinning sharply when moving northwest to southeast.(3)In the middle and upper crust,the North China Basin(NCB)shows slight high-speed anomalies,which may be related to the relatively high rock strength caused by multiple subsidence since the Cenozoic.(4)In the lower crust,the low velocity anomalies are found around the Tangshan-Tianjin,Zhangbei and Taihang Mountain orogenic belt.A significantly high-velocity anomaly is observed beneath the NCB,and we speculate that it may be caused by the underplating and crystallization of the basic mafic magma from the mantle,accompanied by large-scale extension after the lower crust detachment.(5)Located in several regions with strong earthquakes,there is a certain range of(~10 km)high-speed bodies under the sedimentary layer,where the high-speed bodies are wrapped by the low S-wave velocity under them.The difference of rock strength in the crust provides conditions for stress accumulation and earthquake occurrence.