中国海城地震区地壳与上地幔构造特征的研究

研究表明,海城地震区地壳与上地幔构造特征可以归纳为如下四点:1.震区所处的辽南地区,其地壳是由高速与低速相间的成层介质组成,地壳与上地幔结构不论纵向和横向都是不均匀的,且被深大断裂切割为若干块体;2.本区地壳按其界面分布特征可分为上层地壳、中层地壳和下层地壳;3.本区地壳介质在纵向及横向上均存在明显的不均一性;4.海城地震震源区位于耿庄——海城上地幔局部隆起东侧的中层地壳上部。

RESEARCH ON TECTONIC CHARACTERISTICS OF THE CRUST AND UPPER MANTLE IN HAICHENG SEISMIC AREA

Based on the DSS profile data resulting from the deep seismetrical test in the Luyang-Haicheng-Donggou area and data of gravity, earthquake and electromagnetic tests,this paper reported the basic characteristics of the crust upper mantle structure in the earthquake-stricken Haicheng and adjacent areas. Which are summarized as following.1. In South Liaoning province where earthquake always occurs, the crust is composed of layered rocks with high and low speeds alternately. Structure of the crust and upper mantle, either vertically or horizontally, is inhomgeneous and behaves as a number of massifs cut by deep giant fractures. The general pattern of deep tectonics indicates there is a rising up of upper mantle. Local bulges of upper mantle are seen along a belt running between Shenyang and Haicheng by the east side of the main mantle rising. This local belt is also a high density belt.2. According to our analyses, the crust of this area may be classified into the upper, middle and lower crusts. The DSS and electro-magnetic depth-measurement show that the low-speed lawer and low-resistance lawer occur in lower part of the middle crust, and the depths of both layers are approximately the same.3. Obvious unhomogeneity was found both horizontally and vertical in the crust of this area.4. Haicheng Quake source fell on the upper part of the middle crust to the east of the local mantle bulge at Gengzhuang-Haicheng. The low-speed laver becomes thicker here, the average speed in crust the and along the Moho becomes lower too. Deep fractures are obviously observed in the main seismic area, and the altitude, gravity and crustal thickness do not agree to isostatic adjustment. All these are meaningful in the study of origination of earthquakes here in this district.