| 沂沭断裂带重力场及地壳结构特征 |
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| 摘 要： | 沂沭断裂带为郯庐断裂带山东段,新构造运动显著,是华北地区的强震活动带之一。文中收集了该地区的布格重力数据,利用小波多尺度分析方法对重力场进行有效分离,研究区域地壳结构特征及断裂空间展布,并应用Parker变密度模型对区域莫霍面进行反演分析,得到以下几点结论:1)重力区域场显示,沂沭断裂带形成了NNE走向的大型重力梯度带,分隔了鲁西、鲁东地块,成为区域内重要的地球物理分界线。2)重力局部场显示,中上地壳结构复杂,沂沭带内部呈现两堑一垒的重力异常格局,5条主干断裂形成线性梯度带分布于东、西地堑内,鲁西块体的多条NW向活动断裂交切于沂沭断裂带,多数断裂只交切于西地堑,而蒙山山前断裂和苍尼断裂横穿沂沭断裂带;下地壳结构相对简单,发生明显的褶曲构造,表现出大规模高、低密度异常相间排列的典型特征。3)区域莫霍面形态东高西低,沂沭断裂带形成了莫霍面陡变带,造成了东西分异格局,潍坊东—莒县—临沂一线出现莫霍面上隆区,具有强震发生的深部孕震环境。4)区域内地震多发于高、低重力异常转化带之间,特别是活动断裂对应的重力梯度条带之上,地震的发生与断裂活动有着密切的关系,沂沭断裂带地震活动性最强,且东地堑强于西地堑。
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| 收稿时间： | 06 August 2014 |
DEEP STRUCTURES OF YISHU FAULT ZONE DERIVED FROM GRAVITY DATA |
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| Authors: | WANG Xin ZHANG Jing-fa FU Ping-jie GAO Min |
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| Institution: | 1.Key Laboratory of Crustal Dynamics, Institute of Crustal Dynamics, China Earthquake Administration, Beijing 100085, China;2.Shandong University of Science and Technology, Qingdao 266590, China |
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| Abstract: | Yishu Fault zone is the Shandong segment of Tan-Lu Fault zone, which is characterized by remarkable neotectonic activities and is one of the strong earthquake activity belts in North China. Wavelet multi-scale analysis method is applied to separate gravity fields effectively to study the features of crust structures and spatial distribution of faults with collected Bouguer gravity data of this area. Moho depths are inversed by using the variable density model. The following conclusions are concluded: (1)The gravity fields show that the Yishu Fault zone forms a large-scale NNE-striking gravity gradient zone, which separates the western Shandong block and eastern Shandong block as a major geophysical boundary in this area. (2)The local gravity fields show that the structure of mid and upper crust is complex. The gravity anomaly pattern of 1 horst trapped between 2 grabens appears in the Yishu Fault zone and 5 main faults distributed in the east and west grabens form a linear gradient zone. Many NW-striking active faults in Western Shandong block intersect with Yishu Fault zone in the deep part. The majority of these faults intersect to the west graben of Yishu Fault zone. Only Mengshan Fault and Cangni Fault traverse the Yishu Fault zone. The structure of lower crust is relative simple, fold structures are evident, and there is typical characteristics of large-scale high and low density anomalies alternating in the lower crust.(3)In the Moho depths image, the east part is high and the west is low. The Yishu Fault zone forms the Moho abrupt change zone, creating the separating pattern. Uplift of Moho occurs along the east Weifang-Juxian-Linyi regions, providing deep conditions for strong earthquake preparation.(4)Earthquake epicenters are mainly located in conversion zones between the high and the low-density anomaly, especially in the transitional area from the low-density to high-density anomaly. The occurrence of earthquake is closely related to activity of fault. The Yishu Fault zone sees the strongest seismic activity in this area, and the seismicity in east graben is higher than that in west graben. |
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| Keywords: | Yishu Fault zone crust structure Bouguer gravity anomaly wavelet multi-scale analysis seismic activity |
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