华北克拉通东西部过渡带中小地震震源机制及其深部流变特性研究

This project focuses on the earthquakes with magnitude larger than 3 (include 3) that occurred beneath the Taihang Mountain and in the Shaanxi-Shanxi rift system located within the central orogenic belt of North China Craton. According to the report of the China Digital Seismic Network, these earthquakes are distributed from 4 km to 30 km in depth. The tectonic structure of this area is very distinct from east to west and high-quality focal mechanism of small earthquakes occurred there has not yet been clarified. Thus, in this project, we are going to provide detailed information of the small earthquake focal mechanism through systemic waveform inversion in this area. We intend to establish 1-D velocity model by comparing, refining and averaging 3-D velocity model obtained by seismic tomography, deep seismic sounding profile and so on. Based on accumulated digital seismic waveform in decades, the earthquakes occurred since 2002 with magnitude larger than 3 (include 3) will be processed to obtain focal mechanism using CAP waveform inversion method, and focal depth employing identification of surface-reflected depth phases. By combining high-confidence stress tensor derived from Bootstrap Linear Stress Inversion with knowledge of regional tectonic stress state character and the depth variation of plunge angle of principal stresses, this project aims to investigate the connection between small earthquake focal mechanism and the heat flow and rheology of lithosphere, thus provide the seismological basis of North China Craton destruction.

本研究将以华北克拉通东西部构造显著差异的过渡带为研究区域，对太行山构造带和陕西－山西新生代裂陷区在空间上广泛分布的3级以上地震（地震台网报告给出的震源深度为4～30km），进行系统的震源机制波形反演测定，以填补研究区缺乏高质量的中小地震震源机制资料的空白。本项目拟细化华北地区已有的地震层析成像、人工地震勘探等取得的三维速度结构模型，分区构建一维速度模型；充分利用十年来数字地震台网积累的波形记录，对2002年以来发生的3级以上中小地震，利用CAP波形反演方法获取震源机制，通过识别近震距离上的深度震相，精确测定震源深度，辨析台网报告中可能发生的下地壳地震；结合bootstrap重复采样方法反演得到的高置信度的最佳应力张量，综合区域构造应力特征、震源机制主应力轴倾角的深度变化，探讨华北克拉通东西部过渡带中地震活动机制与岩石圈局部热活动和流变特性的关系，为华北克拉通破坏机制的研讨提供地震学依据。

本研究对2008-2014年华北克拉通东西部过渡带地震重新定位，得到震源深度主要集中在0~30km，震源深度从西南向东北方向变浅；对2010-2014年期间太行山和陕西-山西断陷区M3.0级以上76个地震，进行系统的震源机制波形反演测定，填补了研究区高质量的中小地震震源机制资料的空白，研究结果表明该区域主要以正断层和走滑型地震事件为主。结合bootstrap重复采样方法反演得到本项目得到山西断陷盆地及其周边地区主压应力方向为NNE-SSW。