中国西部地区地壳结构特征与强震活动相关性研究

中国西部地区是地震活动十分强烈的地区,天山、阿尔泰、帕米尔和西昆仑都是著名的地震构造带,在这些地震构造带和周边地区发生了多次震级大于5级的强震.本文通过分析西部地区的重力场特征,根据重力数据结合地震剖面、应用Parker-Oldenburg方法反演得到了研究区莫霍面深度,通过对比地震层析成像的反演结果,分析了研究区的地壳结构特征.计算结果表明,研究区地壳结构不均匀特征明显,在造山带地区一般是莫霍面坳陷区,盆地则是莫霍面隆起区,主要造山带地壳速度结构表现为高速区,盆地和主要凹陷区为低速区.根据计算结果和以往强震震中位置分析了地壳构造与强震活动的相关性,西部地区的地震活动与地壳结构的横向不均匀密切相关,强震主要发生在地壳速度变化带附近和地壳速度结构差异较大的地区,在构造应力作用下,这些地壳介质非均匀地区易发生强震,这是中国西部造山带和盆-山边界附近频发强震的构造原因之一.

Characteristicsof crustal structure and their relation with major earthquakes in western China

Major and/or great earthquakes frequently occur in western China,such as the Tian Shan, Altay, Pamir and Kunlun as well-known seismotectonic zones. This paper analyzes the characteristics of the gravity field in western China, inverts the depth of Moho interface by the Parker-Oldenburg method with gravity data and seismic profiles.Through comparison of the results of seismic tomography inversion, we analyze crustal structure of the study area. The results show that the study area is significantly heterogeneous in crustal structure, with main orogenic belts of high-speed while basins and major depressions of low speed.The orogenic belts in the study area are generally Moho depression areas while the basins are the Moho uplift areas. According to the calculation results and epicenter distribution of the study area, we discuss the correlation between crustal structure and major earthquakes. The earthquakes in this region are closely related to crustal heterogeneity, which mainly happen around the crustal velocity change belts and in the regions with great crustal velocity differences. Under the effect of tectonic stress, these crustal non-uniform areas are prone to major earthquakes, which is one of the tectonic reasons for frequent major earthquakes in orogenic belts and near the boundary between basins and mountains in western China.