DISCUSSION ON THE SEISMOGENIC STRUCTURE OF ZHAN-JIANG BAY AREA FROM THE VIEW OF DEEP FAULT SYSTEM INTERPRETED BASED ON THE GRAVITY DATA

doi:10.3969/j.issn.0253-4967.2018.06.010

Abstract

Abstract: The neotectonics in Zhanjiang Bay area is almost the inferred faults and there are not any active faults seen on the ground surface. So it is difficult for research on the seismogenic structure. This paper analyzes and interpretes the gravity data that can reflect the feature of deep faults and then discusses the seismogenic structure of Zhanjiang Bay area in combination with its geology and earthquake activity. There is a huge NEE-trending high gravity gradient belt lying in the coastal region among Guangdong, Guangxi, and Hainan, and Zhanjiang Bay is located in this gravity gradient belt. We analyzed and interpreted more than eighty images obtained with many different methods one by one, then, got the result that Zhanjiang Bay area is embraced by two giant fault belts trending in the NEE and NW direction respectively, and its interior is crossed over by the NE-trending fault belt. These three fault belts are well shown in the gravity images, especially the NEE-trending fault belt and NW one. The gravity isolines and gradient belts or the thick black stripes of the NEE-and NW-trending fault belts are displayed apparently. Also, these gravity structures are good in continuity, extend vastly and cut deeply. What is more, the NEE-trending fault belt plays a leading and region-controlling part. It shows good continuity, and cuts off the NW-and NE-trending faults frequently and intensively. The NW-trending fault belt also is good in continuity and cuts the NEE-and NE-trending faults relatively frequently and strongly, but it is restricted by the NEE-trending one. Last, the continuity of the NE-trending fault is worse and the strength cutting off NE-and NW-trending faults is significantly weak, just in some segments and in the shallow positions. According to the characteristics above and combined with the analyses of geological structure and earthquake activity, the conclusion can be drawn that the NEE-trending fault is the controlling structure and the main seismogenic structure in Zhanjiang Bay area, and the NW-trending fault is the second one. They conjugate and act together. Therefore, Zhanjiang Bay has the tectonic condition for generating M_S=6.5 earthquakes.

Key words: Zhanjiang Bay, gravity data, deep fault, seismogenic structure, NEE-trending fault, NW-trending fault

摘要： 湛江湾地区的新构造基本都是推测断裂，地表并无较大规模的断裂构造显示，这给研究湛江湾地区的发震构造特征带来了困难。文中利用能够反映深部断裂的重力资料，通过解释、分析并结合地质构造与地震活动对湛江湾地区的发震构造予以讨论。湛江湾构造区位于粤桂琼交界沿海地区一条规模宏大的NEE向高重力梯度带内。经过逐图详细分析解释80多幅成果图像，得出湛江湾构造区就位于NEE向与NW向2个巨型断裂系内一个范围不大的交会区间，而规模亦较大的NE向断裂斜贯中部。这3组断裂带在重力资料成果图像中都有较明显的表现，尤其是NEE向断裂和NW向断裂，其重力异常等值线或梯度带明显，浓黑条带显著，重力结构好，规模大，切割深。NEE向断裂起区域控制性作用，具有明显的主导地位，切割NW向和NE向断裂的频次高，力度大；NW向断裂规模也大，活动性也强，但仍受NEE向断裂的控制，多被其截断；NE向断裂截切NEE向、NW向断裂仅限于局部段，频次低，深度浅。结合地质构造特征及地震活动分析认为，湛江湾地区以NEE向断裂为控震构造，发震断裂以NEE向断裂为主，NW向断裂为辅，两者共轭活动，其具备发生6.5级地震的构造条件。

关键词: 湛江湾, 重力资料, 深部断裂, 发震构造, NEE向断裂, NW向断裂

CLC Number:

P315.2

BI Li-si, REN Zhen-huan, YE Xiu-wei, WU Ye-biao, LIU Tian-you, QIAO Ji-hua. DISCUSSION ON THE SEISMOGENIC STRUCTURE OF ZHAN-JIANG BAY AREA FROM THE VIEW OF DEEP FAULT SYSTEM INTERPRETED BASED ON THE GRAVITY DATA[J]. SEISMOLOGY AND GEOLOGY, 2018, 40(6): 1332-1348.

毕丽思, 任镇寰, 叶秀薇, 吴业彪, 刘天佑, 乔计花. 基于重力资料从深部断裂系统讨论湛江湾地区的发震构造[J]. 地震地质, 2018, 40(6): 1332-1348.

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