红河断裂带三维运动学和动力学模型构建及其强震危险性分析

In the recent years, a series of large earthquakes, e.g., 2008 M8 Wenchuan earthquake, 2011 M9 Tohoku-Oki earthquake, unexpectedly occurred on the fault whose seismic moment release is low. Red River Fault zone (RRF), as the west-south boader of the Chuandian rhombic block, runs for hundreds of kilometers. Such a long distance is required for a possible large earthquake. Nevertheless, similar as the Longmenshan Fault on which the Wenchuan earthquake occurred, RRF has low seismic moment release level and low slip rate. According to the geological surveys, the major part of RRF experienced significant tectonic activities during the Holocene, and thus, RRF might be a seismic gap lasting for at least hundreds of years. Therefore, it is important to evaluate the strain state along RRF and its seismic potential. We explore in the project (1) the tectonic correlation from surface to the deep structures of the RRF and its surrounding secondary faults from the aspect of geological survey; (2) the creeping/locking state along the fault that is learned from the GPS-measured displacement rates, for quantifying the strain accumulation rate along RRF; (3) the dynamical correlations between RRF and its surrounding secondary faults and strain partition based on three-dimensional dynamical model in the region. Based on the detailed kinematic and dynamical model, we try to understand the dynamical behaviors of RRF and its seismic potential.

近年来的一系列大地震，如2008年汶川大地震和2011年日本东北大地震，均出乎意料地发生在现代地震活动水平很低的断层。红河断裂带是川滇菱形块体的西南边界，长度几百公里，具有发生大地震的必备条件。但与汶川大地震的发震断层龙门山断裂类似，红河断裂带的现代地震活动水平和滑动速率都很低。然而，地质调查等研究表明，红河断裂带的主体段落在全新世仍然有显著的构造活动，可能是一个平静了至少几百年的地震空区，因此，评价红河断裂带的应变积累状态和强震危险性尤其重要。本项目分别（1）从地质构造角度分析红河断裂带及其周围主要次级断裂的深浅构造耦合；（2）基于现代GPS速度场资料反演断层蠕滑闭锁分布，从而理解红河断裂带的应变积累状态；（3）构建三维区域动力学模型，研究红河断裂带与周围主要次级断裂的动力学关联和应变分配。通过详细的运动学和动力学建模，本项目试图理解红河断裂带的区域动力学特征和强震危险性。

本项目针对红河断裂带的研究，主要开展以下三方面内容（a）从地质构造角度分析红河断裂带及其周围主要次级断裂的深浅构造耦合；（b）基于现代GPS速度场反演断层蠕滑闭锁分布，从而理解红河断裂带的应变积累状态；（c）构建三维区域动力学模型，研究红河断裂带与周围主要断裂的动力学关联和应变分配。通过详细的运动学和动力学建模，本项目试图理解红河断裂带的区域动力学特征和强震危险性。通过该项目的开展，获得如下认识：（1）经过多个深度剖面的深-浅构造耦合分析，红河断裂带在深度上有明显的扭曲，并形成几十至上百公里宽的断层带；（2）根据GPS约束的红河断裂带的深部滑动速率较低，～2mm/a；（3）红河断裂带底部的下地壳塑性变形的模式与红河断裂带的走向完全不一致，这有可能是导致现今红河断裂带地震活动水平低的根本原因。