中国东北地区下方660km间断面研究

A study on 660km discontinuity beneath northeast China

围绕中国东北地区下方俯冲的西太平洋板块是停滞在地幔过渡带内水平向西伸展,还是穿透660km间断面直接进入下地幔,始终是一个具有争议的问题.本文基于P--SV转换波对速度间断面的敏感性,利用中国数字地震台网在东北地区布设的136个固定地震台站记录到的远震波形数据,通过提取台站下方的接收函数并采用共转换点(CCP)叠加技术,得到了该区域660km间断面的起伏变化图像.结果显示,东北地区下方660km间断面下沉幅度超过20km的区域主要集中在44°N以南、东西跨度约400km的范围内.660km间断面的下沉表明西北太平洋板块俯冲到了中国东北地区下方,在较小区域范围内观测到的较大深度异常可能暗示着俯冲板片穿透660km间断面直接进入了下地幔.

It is highly debated on whether the subduction Pacific slab becomes stagnant in the transition zone and extends horizontally or it penetrates into the lower mantle when the leading of the Pacific slab reaches to a depth of 660 km beneath northeast China.Taking advantage of the sensitivity of P--SV conver-sions to the velocity discontinuities,we employ receiver function method to con-strain the topography variation of the 660 km discontinuity beneath northeast China using common conversion point （CCP）stacking.The teleseismic data recorded by 136 permanent stations operated by CDSN in northeast China are used in this study.Our results show that the 660 km discontinuity deepening more than 20 km was observed in the region to the south of 44＆#176;N with length about 400 km in the east-west direction.The local depression of the 660 km dis-continuity supports that the Pacific subduction slab has reached northeast China and it may penetrates into the lower mantle locally.