重力不稳定性与亚洲内陆三角形地震区地球动力学特征

GRAVITATIONAL INSTABILITY AND CHARACTERISTICS OF GEODYNAMICS IN THE ASIAN INTRACONTINENTAL TRIANGULAR SEISMIC AREA

本文研究了亚洲内陆三角形地震区的岩石圈厚度、上地幔顶部Pn波速度、上地幔密度分布、地壳结构、现代构造运动及地震活动等特征。认为该区内存在着地幔分异物质多元底辟现象,致使岩石圈减薄及地壳增生变厚,而巨厚的地壳处于重力不稳定状态,地壳物质发生流变,该区内现代构造运动与地震活动均与此有关。作者认为,重力是导致本区上地幔及地壳发生构造运动的主要力源之一。

Since 1900 the Asian intracontinental great earthquakes (M≥8.0) mainly have distributed in the three boundary zones of a vast triangle-shaped area, in addition, within this area the seismic activities are rather strong. The three boundary zones in turn are as follows: the Himalayas, the mountainous regions from Pamirs to West Mongolia, and the North-South Tectonic Belt in China. The author terms this area as the Asian Intracontinental Triangular Seismic Area (AITSA). Based on the characteristics of the lithosphere thickness, the values of Vpn, the distribution of the upper mantle density, the isostatic gravity anomalies, the crustal structure, recent tectonic movement and seismic activities, the author infers preliminarily that, under the action of the gravity force, beneath AITSA there exists multi-diapirism from asthenosphere. Owing to this process of the upper mantle materials, the thinning of the lithosphere as result of erosion and the thickening of the crust clue to accretion may take place. the thickened crust is in a state of gravitational instability, resulting in the crustal materials flow, which controls the recent tectonic movements and the seismic activities within the crust. According to this paper, the gravity may be the major one of the un-negligible tectonic driving forces in the AITSA.