地幔对流对断层应力积累的作用：以蒙古地区为例

In conventional studies of mechanism of earthquake occurrences and stress evolution on faults, the collision and compression process between tectonic blocks and interaction among faults are usually considered. These studies can explain the occurrences of earthquakes to a certain extent, but there are still some doubts, such as energy source of 4 earthquakes with M≥8 in Mongolia during 1905~1957, which can't be explained by the process of the India-Eurasia collision. It is suggested that the active mantle convection exist under the Mongolia Plateau, which, at least partly, controlled the regional tectonics. Therefore, the stress field of mantle convection under the lithosphere may explain the energy and mechanism of the earthquakes in this region. In this study, we will construct a 3D lithosphere model controlled by the stress field of mantle convection based on the results of lithospheric rheological structure and pattern of mantle convection in this region, and quantitative analysis the effects of mantle convection on stress accumulation of active faults. This study is desired to be benefit for understanding the effects of mantle dynamics on stress state of the lithosphere and faults system, and the mechanism of earthquake occurrence.

在以往的地震成因和断层应力演化研究中，通常考虑的是块体之间碰撞挤压的过程以及断层之间的相互作用。这些研究能够在一定程度上解释地震发生的原因，但仍然存在一些困惑，例如：蒙古高原及邻区1905-1957年发生的四次8级以上地震的能量来源难以简单归因于印度-欧亚大陆碰撞挤压的远场效应。研究表明，蒙古-贝加尔地区存在活跃的地幔对流系统，并且在该区域的构造动力学过程中扮演着十分重要的角色，因此，来自于岩石层底部的地幔对流应力场成为地震能量来源可能的机制和解释。本项目申请利用蒙古-贝加尔地区岩石圈流变结构以及地幔对流场的研究成果，构建地幔对流应力场作用下的三维岩石层结构模型，定量分析蒙古高原及邻区地幔对流对断层库仑破裂应力积累的作用与贡献。本项目对深入研究地幔动力学过程对岩石层及断层系统应力状态的影响，全面认识地震孕育产生的机理等，具有重要的科学意义。

本项目利用多种地球物理（地震波、重力、地形、地表热流等）和地球化学观测资料反演了岩石圈的温度和化学组分结构，利用温度和化学组分结构研究岩石圈的强度及流变性质，作为研究岩石圈底部加载和浅层应力场耦合的基础；研究了沿断裂带应力的传输和演化过程，定量的分析了应力积累与地震活动性之间的关系；基于贝加尔裂谷岩石圈和流变结构模型，构建了沿NW-SE向横穿贝加尔裂谷的二维岩石圈模型，以地幔对流力学和热输入作为边界条件，计算在地幔对流作用下岩石圈的形变过程，分析了在拉张作用与地幔上涌作用下对贝加尔裂谷形成的影响。本项目已经发表国内外SCI论文6篇，资助培养博士研究生3名，硕士研究生1名。