【作者】 朱爱斓；

【导师】 徐锡伟； 尹京苑；

【作者基本信息】 中国地震局地质研究所 ， 构造地质学， 2006， 博士

【摘要】 间震期背景地震的活动性与活动断裂的现今滑动习性密切相关,而精确的震源位置是研究地震活动性的重要基础数据。本文利用双差地震定位法对川西地区1992~2002年发生的小震作了重新定位,基于高精度的相对震源参数资料,对川西地区的一些构造问题进行了探讨。研究了震源深度分布与地壳流变结构的关系,初步探讨了研究区的地壳变形特征;重点剖析了沿鲜水河-安宁河-则木河断裂带和龙门山推覆构造带的地震活动性及其所揭示的深部结构面、活动信息与地表断裂结构的关系;沿鲜水河-安宁河-则木河断裂带进行了b值与局部复发时间TL值的空间扫描,分析了断裂带的现今活动习性、应力应变水平以及可能存在的凹凸体;通过卫星影像解译、震源空间分布分析、前人野外地质调查工作的资料整理,建立起控制川西地区现今构造变形的主干活动断裂的三维空间几何结构模型与初始运动模型,采用各向同性半无限弹性空间的三维断裂位错模型,以本区域高精度、高密度GPS速度场为约束,反演了区域内主要断裂的现今深部滑动速率,探讨了研究区的深浅构造关系。本文的研究是在综合利用了前人大量的地表地质调查、野外填图、深部地球物理探测、震源机制等研究成果的基础上而开展的,主要研究内容及取得的成果概述如下:1.小震重新定位使用Waldhauser与Ellsworth 2000年提出的双差地震定位法对四川地震台网观测报告中自1992到2002年间记录的川西地区13367个小震作了重新定位,获得了10215个地震重新定位的震源参数。重新定位后,定位均方根残差得到显著降低,地震分布明显线性集中,显示出与活动断裂更加密切的关系,表明事件之间的相对定位精度得到显著提高,为活动构造现今运动状态分析提供高质量的基础数据,揭示出诸多为常规定位地震所模糊掉的重要构造变形信息。2.研究区主要活动断裂重新解译为利用重新定位的地震数据准确地反映并揭示活动断裂的现今活动状态,在前人大量的野外地质调查及活动断裂填图资料的基础上,采用ETM卫星影像处理,重新解译了研究区主要活动断裂的空间展布,为进一步探讨活动断裂与地震活动的关系,正确构建活动断裂三维几何结构模型提供了重要基础。3.震源深度分布与地壳流变结构关系研究当前流变学研究的一个重要发展方向是震源深度分布与地壳流变结构关系的对比研究。尽管不同地区的构造背景、地壳结构相差很大,国内外大量学者在世界范围内许多地区所作的震源深度与流变结构的对比研究发现,震源深度分布与岩石圈的流变分层性有着较好的对应关系。此认识为岩石圈流变结构及其力学性质随深度变化模型的建立给予了地震学有力的更多还原

【Abstract】 Western Sichuan, located in the southeast borderland of the Tibetan plateau, is one of the most seismically active regions in continental China, which is characterized by active tectonic block movement controlled by large-scale,rapidly slipping active faults. Deformation of this region is thought to be localized along the boundary faults. To investigate detailed deep structures and slip behavior of the major active faults in the interseismic interval within this region using microseismicity, I performed double-difference relocations for 10,215 small earthquakes from a catalog of over 13,000 that occurred between 1992 and 2002. The relocated seismicity becomes highly organized in space, compared to the diffuse view seen in the routine locations, and focuses sharply along the surface traces of faults reinterpreted using the ETM satellite image, indicating that the precision of the relative relocations gets improved greatly, which enables me to address some problems in active tectonic deformation within this region.Relationship between hypocentral depth distribution and crustal rheological structureMost relocated events in western Sichuan occur within the upper crust at depths of 0-15km, and fewer at 20-50 km depths. There appears an aseismic layer between 15 and 20 km depth in the western Sichuan plateau, whereas no such aseismic layer in Sichuan basin. On the basis of fault friction law and rock rheological experimental data, the crustal strength envelopes (stress limit) for western Sichuan plateau and Sichuan basin were calculated respectively to investigate the relationship between the hypocentral depth distribution and the rheological structures, and the deformation feature of the aseismic layer as well. The result shows that the hypocentral depth distribution agrees with the crustal rheological structure well as most earthquakes occur in the brittle zone, and the aseismic layer in western Sichuan plateau corresponds to the ductile granite zone within the upper crust at depths of 14-19 km, while the earthquakes in the lower crust to the half-brittle zone of gabbro. The existence of the aseismic layer is likely to be associated with low velocity zone within the upper crust, which features the orogenic crust structure of western Sichuan plateau. It is proposed that the existence of this aseismic layer may result from eastward extrusion of material from the Tibetan plateau and clockwise rotation activity of the Sichuan-Yunnan block.Microseismicity along the Xianshuihe-Anninghe-Zemuhe fault zoneThe Xianshuihe-Anninghe-Zemuhe fault zone is a large left-lateral strike slip fault zone in western Sichuan, which forms the eastern boundary of the Sichuan-Yunnan rhombic block, and the eastern margin of the Tibetan plateau as well. The deep structures delineated by the relocated seismicity correspond to the surface faulting well, especially in the segmentation feature. The variation in the更多还原