利用重力资料探讨宁夏地区地壳结构的基本形态及其与强震活动的关系

本文利用布格重力异常资料经过“剥皮”、“上延”反演计算,得出了宁夏地区十六条剖面的莫霍面及康拉界面的埋藏深度,並绘制出宁夏及其邻近地区的深部重力异常图、莫霍面等深度平面图。此结果与地质构造、测深资料基本相近。由此得出如下认识:宁夏地区的地壳厚度比东部的陕西地区增厚1—5公里,比西部的甘肃地区薄6公里左右。全区有几个莫霍面凹陷区和隆起区,即银川—平罗莫霍面凹陷区、中卫—中宁莫霍面隆起区、吴忠—马家滩莫霍面凹陷区、海原—李俊堡莫霍面凹陷区。另外还清楚地看到,在宁夏南部地区,大致以大、小罗山、预旺、泾原一线为界,往东地壳厚度逐渐变薄,往西地壳厚度逐渐变厚。历史上宁夏地区的强震位置恰巧与上述凹陷区和隆起区之间的变化梯度带相吻合。

BASIC FORM OF CRUST STRUCTURE OF NINGXIA AREA AND RELATION BETWEEN THE FORM AND ACTIVITIES OF STRONG EARTHQUAKES

Based on the sixteen gravity sections chosen, the author has calculated anomalous value of gravity in the depths of the earth. Basic form and degree of hidden depth in the earth of the Moho discontinuity have been got. The thickness of the crust in Ningxia area is 1-5KM greater than that of Shanxi area and 6 KM less than that of Gansu area. There are three segs and one upheaval of the Moho discontinuity in this area. They are the Yinchuan-Pengluo seg, the Wuzhong-Majiatan seg, Haiyuan-Lijunpo seg and the Zhongning-Zhongwei upheaval. On the south of Ningxia area they are generally bounded by the Daluoshan Mountain, the Xiaoluoshan Mountain, Yuwang and Jingyuan. Curst is getting thiner and thiner on the east of the bound and thicker and thicker on the west of the bound. Historical strong earthquakes just occurred on the stair belt between the segs and the upheaval of Moho dicontinuity in Ningxia area.