根据GPS和InSAR测量推断2008年MW7.9汶川地震的断层形状和破裂分布

本研究对2008年M W7.9汶川地震的同震破裂问题进行重新研究。精确的断层几何结构和滑动分布为断层系统的滑动习性和地震破裂提供了关键性资料。本研究采用所有可获取的大地测量数据,构建比前人研究更加真实的地球结构和断层模型,采用非线性反演策略最优地确定了断层几何形状和滑动分布。相比于均匀弹性半空间模型和两侧一致的成层弹性结构模型,本研究在北川断层两侧采用不同的成层弹性结构模型,使数据拟合度有较大改善。结果表明:(1)北川断层为铲形断层,近地表断层倾角从西南端约36°增加到破裂终止东北端约83°;(2)断层破裂模式自西南端的显著的逆冲类型变化至东北端的右旋走滑类型;(3)大部分断层的破裂峰值接近地表:虹口附近逆冲约8.4m,右旋走滑约5m;北川附近逆冲约6m,右旋走滑约8.4m;(4)滑动峰值位于几何形状较为复杂的断层附近,意味着地震类型和破裂传播由断层区的几何障碍确定。这类障碍主要是伴随控制左阶不连续的右旋压缩体系而存在的;(5)近地表20km深度的断层释放的地震矩为8.2×1021 N·m,对应于MW7.9的事件。映秀—虹口段、北川—平通段、青川附近以及南坝附近的局部滑动集中区释放的地震矩分别等价于M W7.5,MW7.3,MW7.1,MW6.7的事件;(6)断层几何结构及其运动学特征符合青藏高原东缘跨越中地壳滑脱层的上下不同的地壳形变模型,上部以脆性的逆冲断层活动为主,下部为流变水平缩短和垂直增厚机制。

Seismicity of Global Tectonic Systems Obtained from the Harvard CMT Catalogue

Earthquake is the best information source for describing the present-day crustal tectonic zones and crustal stress field, containing comprehensive and abundant geodynamic connotations. Based on the distribution of global earthquakes and their kinematic and dynamic characteristics, the most active global-scale tectonics can be divided into three first-order tectonic systems: the Circum-Pacific deep subduction tectonic system, the mid-oceanic ridge tectonic system, and the continent-continent shallow underthrusting tectonic system using the Harvard CMT catalogue that provides various parameters of hypocenter. Furthermore, the differences of fault types, seismicity, and distribution of focal depths in different tectonic systems are discussed as well. The results show that different tectonic system possesses different environment and geodynamics.

An Analysis on Correlativity between Large Earthquakes in the Hindu Kush-Pamir and Tienshan Seismic Zone

In this paper,we introduce the tectonic setting,historical earthquake focal mechanisms and geodynamic environment of Tienshan and its neighboring regions, and draw a conclusion that large earthquakes in the Tienshan seismic zone are governed mainly by the pushing from Hindu Kush-Pamir syntax. Secondly,the relationship of large earthquakes in the Hindu Kush-Pamir region and the Tienshan seismic zone is investigated,and synchronization features are found existing in the grouped large earthquakes between the large earthquakes in two regions. The relationship between intermediate-focus large earthquakes in Hindu Kush-Pamir and shallow large earthquakes in the Tienshan seismic zone is also discussed. The same synchronization characteristics are found,and the intensity and frequency of intermediate-focus earthquakes are fiercer, while large earthquakes in the Tienshan seismic zone are more intense,with a wider distribution range. The above results confirm the geodynamic correlativity between Hindu Kush-Pamir and the Tienshan seismic zone from the viewpoint of seismicity.

Tectonic dynamics and correlation of major earthquake sequences of the Xiaojiang and Qujiang-Shiping fault systems, Yunnan, China

The N-S trending Xiaojiang fault zone and the NW-SE trending Qujiang-Shiping fault zone are adjacent active fault systems and seismogenic zones associated with strong and major earthquakes in Yunnan, China. To understand the interaction of the two fault systems, and its probable influence on earthquake occurrences, this paper conducts a synthetic study based on data of active tectonics, historical earthquakes, relocated small earthquakes, GPS station velocities and focal mechanism resolutions. The study makes several conclusions. （1） The active southward motion of the western side of the Xiaojiang fault zone （i.e. the side of the Sichuan-Yunnan block） has a persistent and intensive effect on the Qujiang-Shiping fault zone. The later fault zone has absorbed and transformed the southward motion of the western side of the former fault zone through dextral strike-slip/sheafing as well as transverse shortening/thrusting. （2） Along the Xiaojiang fault zone, the present sinistral strike-slip/sheafing rate decreases from 10 and 8 mm/a on the northern, central and central-southern segments to 4 mm/a on the southern segment. The decreased rate has been adjusted in the area along and surrounding the Qujiang-Shiping fault zone through reverse-dextral faulting and distributed sheafing and shortening. （3） The tectonic-dynamic relation between the Xiaojiang fault zone and the Qujiang-Shiping fault zone is also manifested by a close correlation of earthquake occurrences on the two fault zones. From 1500 to 1850 a sequence of strong and major earthquakes occurred along the Xiaojiang fault zone and its northern neighbor, the Zemuhe fault zone, which was characterized by gradually accelerating strain release, gradually shortening intervals between M≥7 events, and major releases occurring in the mid to later stages of the sequence. As a response to this sequence, after an 88-year delay, another sequence of 383 years （from 1588 to 1970） of strong and major earthquakes occurred on the Qujiang-Shiping fault zone, and had the same features in accelerating strain release and its temporal course. （4） Since there has been no M≥7 event for 177 years on the Xiaojiang fault zone, the potential risk of a strong or major earthquake occurring on this fault zone in the future should be noticed and studied further.