鲜水河-小江断裂带地震分段活动特征的数值模拟研究

The comprehensive study of segmented seismicity is the basis of strong seismic hazard assessment in the fault zone. The limitation of earthquake catalog leads to the insufficient understanding of the occurrence regularity and segmented activity of fault zone earthquakes, and it is still very difficult to assess the long-term strong seismic risk of the whole fault zone. In order to understand the difference of seismic activity in Xianshuihe-Xiaojiang fault zone more comprehensively and to further evaluate the seismic risk of the fault zone, a three-dimensional viscoelastoplastic finite element model including Xianshuihe-Xiaojiang fault zone was established in this project. The stress and strain distribution of each segment of the fault zone and the long-term artificial earthquake catalog are calculated by simulating the interseismic loading, coseismic release and postseismic adjustment deformation process of the seismic cycle. By analyzing the influence of the controlling factors such as fault geometry, fault strength and lithosphere structure on the deformation and seismic activity of each segment of the fault zone, the mechanism of segment activity of the fault zone is revealed. Based on the simulated artificial earthquake catalog, the seismicity characteristics of each segment of the fault zone, such as earthquake recurrence rule, magnitude-frequency relationship and so on, are analyzed and given. The results of the project will be of great reference to the long-term seismic risk assessment of the Xianshuihe-Xiaojiang fault zone.

分段地震活动性的综合研究是断裂带强震危险性评估的基础。有限的地震目录导致对断裂带地震发生规律和分段活动性的认识仍存在不足，断裂带整体的长期强震危险性评估仍面临很大的困难。为更全面深入地认识鲜水河-小江断裂带的地震分段活动差异，并进一步评估该断裂带的地震危险性，本项目拟建立包含鲜水河-小江断裂带的三维黏-弹-塑性有限元模型。通过模拟地震循环的震间孕育、同震释放及震后调整的变形过程，计算断裂带各分段的应力、应变时空分布及长期人工地震目录。通过对比分析各种控制因素（断层几何结构、断层强度及岩石圈结构等）对断裂带各分段的变形及地震活动的影响，探索断裂带分段活动机制。通过分析人工地震目录，得出断裂带各分段的地震复发规律、震级-频度关系等地震活动性特征。项目成果将对鲜水河-小江断裂带的长期地震危险性评估具有重要参考意义。

鲜水河-小江断裂带位于川滇菱形块体的东边界，是一条活动剧烈的大型走滑断裂带。对该断裂带进行地震活动性和强震危险性研究，具有十分重要的社会意义和科学意义。针对本项目研究目标，作了以下3个方面的研究内容：1、为更全面深入地认识鲜水河-小江断裂带的地震分段活动差异，并进一步评估该断裂带的地震危险性，建立了包含鲜水河-小江断裂带的三维黏-弹-塑性有限元模型；模拟了地震循环的震间孕育、同震释放及震后调整的变形过程，计算了断裂带各分段的应力、应变时空分布及长期人工地震目录；通过分析人工地震目录，获得了断裂带各分段及整体的地震复发周期、变异系数等地震活动性特征；2、利用青藏高原东南部最近更新的GPS测量数据和该地区的综合地震目录，对鲜水河-小江断裂带沿线的地震矩释放和积累进行了详细的对比；对比结果指示了该断层系统的潜在地震危险的位置；3、建立了包含川滇块体主要断层系统的三维粘弹塑性有限元模型，模拟和研究了青藏高原东南部主要断层上的长期地壳变形、应变分配和滑移速率。探索了断层几何形、断层配置、岩石圈非均质性和地形载荷等主要因素对断层滑移率的影响，研究了断层相互作用和断层活动对地壳挤出变形的影响；研究结果表明了断裂长期相互作用关系及其对地壳挤出变形的重要影响。本项目的相关研究内容对认识鲜水河-小江断裂系的分段地震活动特征及并探索潜在的地震危险性具有重要意义。

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