ISOSTATIC GRAVITY ANOMALY, STRUCTURAL FEATURES AND SEISMICITY OF NORTH CHINA CRATON

doi:10.3969/j.issn.0253-4967.2015.02.012

Abstract

Abstract:

Isostatic gravity anomaly is considered a sign of the isostatic state of the crust, and studies show that the isostatic state of crust is closely connected with the structural features and seismicity in many areas. In order to investigate the isostatic state of crust and to understand its relation to structural features and seismicity in North China Craton, a new isostatic residual gravity map of North China Craton has been computed using recently released earth gravitational model and digital terrain models. Free-air gravity anomalies of North China Craton have been prepared using the gravity data set of Earth Gravitational Model 2008(EGM2008). EGM2008 data set is believed to be reliable and studies show that EGM2008 free-air gravity anomalies have a general accuracy of 10.5mGal(1mGal=10^-3cm/s²)in China. The topographic-isostatic corrections were computed based on an Airy-Heiskanen model of local compensation using a strict algorithm based on digital elevation model(DEM), the average crust thickness of the study area was derived from CRUST2.0, and the topographic and bathymetric data sets were derived from digital elevation model ASTER GDEM 2009(1arc second resolution)and ETOPO1(1arc minute resolution)respectively. Topographic-isostatic corrections were then added to the free-air gravity anomalies to determine the isostatic gravity anomalies of North China Craton with a gridding resolution of 5arc minutes. According to the results of calculations, distribution of isostatic gravity anomalies and its relations to structural features and seismicity of North China Craton were discussed. The results indicate that the spatial distribution of isostatic gravity anomalies is remarkably uneven in North China Craton, and isostatic gravity anomalies are very different between different fault blocks. Isostatic gravity anomalies of North China Craton are mainly controlled by neo-tectonic movements, and are significantly influenced both by lateral variations in crust density and deep structures. The close relation between isostatic gravity anomalies and neo-tectonic movements may imply that there are crustal features that are not compensated regionally and isostatic disequilibrium in North China Craton. The results also indicate that there are some connections between the distributions of isostatic gravity anomalies and seismicity in North China Craton, earthquakes tend to occur around areas with remarkable high or low isostatic gravity anomalies and at transition zones between positive and negative gravity anomalies, and we suggest that special attention should be paid to areas with similar isostatic gravity anomaly characteristics when performing seismic hazard analysis.

Key words: isostatic gravity anomaly, North China Craton, seismicity, structural features, Earth Gravitational Model

摘要：

均衡重力异常是地壳均衡状态的标志, 地壳均衡状态与构造特征及地震活动密切相关。文中基于高阶地球重力场模型EGM2008自由空气异常, 采用高精度数字地形模型(DEM)ASTER GDEM 2009和ETOPO1分别作为陆地和海底地形数据, 通过基于DEM的严密地形-均衡改正方法计算得到华北断块区5'×5'网格分辨率的Airy均衡重力异常。根据计算结果讨论了华北断块区均衡重力异常分布特征, 并探讨了区内均衡重力异常与构造特征、地震活动的关系。结果表明, 华北断块区均衡重力异常空间分布极不均匀, 表现出明显的断块差异性; 区内均衡重力异常大小主要受新构造运动控制, 是地壳表层物质密度横向变化和深部构造差异共同作用的结果, 构造运动对均衡重力异常的显著影响说明华北断块区地壳均衡调整尚未完成; 华北断块区地震活动和均衡重力异常之间有一定的联系, 地震活动在显著的均衡重力异常高值区或低值区周围及正负均衡重力异常区过渡部位分布较为集中。

关键词: 均衡重力异常, 华北断块区, 地震活动, 构造特征, 地球重力场模型

CLC Number:

P315.72⁺6

LI Zhe-jun, XU Ru-gang, ZHANG Wei-jing, ZHANG Yi, LI Hui, YANG Guang-liang, LONG Jian-feng. ISOSTATIC GRAVITY ANOMALY, STRUCTURAL FEATURES AND SEISMICITY OF NORTH CHINA CRATON[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(2): 496-509.

黎哲君, 徐如刚, 张玮晶, 张毅, 李辉, 杨光亮, 龙剑锋. 华北断块区均衡重力异常、构造特征及地震活动[J]. 地震地质, 2015, 37(2): 496-509.

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