川西藏东地区的地壳均衡异常及其与地震分布的关系

川西藏东地区是青藏高原物质东移、转而向东南运移的通道地域,该处强烈的构造活动和频发的地震即是由于其深部物质的分异、调整和运移所致.为此,在该地域沿30°N设置了一条跨越特提斯构造域和扬子克拉通不同构造单元的剖面,依据Airy重力均衡理论求取该剖面沿线的理论均衡地壳厚度,并与根据天然地震和人工源地震资料所求得的实际地壳厚度进行对比分析,以探讨该区壳、幔物质的地壳均衡状态.研究结果发现,在本剖面沿线呈现出两处大的均衡异常区,即与四川盆地相比其差异显著,均衡异常强度高、且范围广.在此基础上通过对地壳重力场均衡效应与强烈地震活动之间关系的分析与探讨.认为存在均衡异常的地区是强震发生的主要地带,而由均衡区向不均衡区过度的均衡异常梯度带则是强震预防的重中之重.

The crustal isostatic anomaly beneath eastern Tibet and western Sichuan and its relationship with the distribution of earthquakes

The area of west Sichuan and east Tibet is the channel where the deep materials of the Tibetan plateau flow eastward and turn to southeast. Due to the strong differentiation, adjustment and movement of the deep materials in this area, strong tectonic activities and earthquakes occur frequently here. Hence, a profile across the Tethyan tectonic domain and the Yangzi craton has been set along the 30°N latitude. And the theoretical isostatic crustal thickness has been calculated according to the Airy isostatic theory and compared with the crustal thickness obtained from both the active and passive seismic sounding data, so as to discuss the isostatic state of the area. The result reveals that there exist two non-isostatic regions along this profile, that is to say, compared with the stable Sichuan basin, the crusts of these two regions are in quite a non-isostatic state. Based on this result, we have analyzed and discussed the relationship between isostatic anomaly and the distribution of strong earthquakes. Our result suggests that the non-isostatic area is the main zone where strong earthquakes occur frequently, and the steep gradient belt of the non-isostatic zone is the place worth more attention concerning earthquake prediction.