邢台强震区的深部构造对强震孕育影响的三维数值模拟
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摘要
为了研究地壳结构特征与强震孕育的关系,运用三维有限单元法,计算了邢台地震区壳内应力场的扰动状态。结果表明:地壳内深、浅断裂的存在,造成沿直立断层带的应力相对集中和不同部位的变化。在其上部出现平均应力和水平剪应力的增加,中下部出现平均应力的减小和水平剪应力的增加。前者有利于弹性位能的高度集中和主破裂的发生,后者有利于主破裂前蠕滑的发生。地壳内高速体、低速体、深断裂、莫霍面隆起是孕育强震的主要构造因素,但影响程度,范围、形式不同,高速块体是应力增强的体;直立断层带上及其邻近应力集中程度最高,应力变化梯度最大,是产生震前预滑及主余震发生的有利部位;莫霍面隆起加剧高速体内的应力增强,加大断层带上的应力变化梯度而有利于地震的孕育和发生。
Using 3-D finite element method the state of stress field disturbance in Xingtai earthquake area is simulated. The corresponding results indicate that the existence of deep and shallow faults causes a different stress concentration around them. In the upper section of the vertical fault the mean stress and the horizontal shear thress increase, while in the central and the low section the mean stress decreases and the horizontal shear stress increases' respectively. The former should be beneficial to the accumulation of the elastic potential energy and to the creation of the main rupture. The latter should be beneficial to the creeping slip before the main rupture. The existence of the combined high-low velocity body, vertical fault beeply buried in the crust and the upward movement of upper mantle are the important structural factors for earthquake preparation. The high velocity body is the main part for stress concentration. The creeping slip before an earthquake and the occurrence of main shock should take place within or near the vertical fault, as the stress concentration and the graient of stress change are biggest around there. The upward movement of upper mantle augments the stress concentration level greatly. This should raise the risk of the preparation and occurrence of an earthquake.
Using 3-D finite element method the state of stress field disturbance in Xingtai earthquake area is simulated. The corresponding results indicate that the existence of deep and shallow faults causes a different stress concentration around them. In the upper section of the vertical fault the mean stress and the horizontal shear thress increase, while in the central and the low section the mean stress decreases and the horizontal shear stress increases' respectively. The former should be beneficial to the accumulation of the elastic potential energy and to the creation of the main rupture. The latter should be beneficial to the creeping slip before the main rupture. The existence of the combined high-low velocity body, vertical fault beeply buried in the crust and the upward movement of upper mantle are the important structural factors for earthquake preparation. The high velocity body is the main part for stress concentration. The creeping slip before an earthquake and the occurrence of main shock should take place within or near the vertical fault, as the stress concentration and the graient of stress change are biggest around there. The upward movement of upper mantle augments the stress concentration level greatly. This should raise the risk of the preparation and occurrence of an earthquake.
引文
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9 孙武城.李松林.杨玉春.华北东部地区地壳结构的初步研究.地震地质,1985,7(3) :1-11 SUN Wu-Cheng, LI Song-Lin. YANG Yu-Chun. Preliminary study on crustal structures in the east of North China.Seismology and Geology (in Chinese), 1985, 7(3) : 1--11
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2 王椿镛,张先康,吴庆举等.华北盆地滑脱构造的地震学证据.地球物理学报,1994,37(5) :613-619 WANG Chun-Yong, ZHANG Xian-Kang, WU Qing-Ju, et al. Seismic evidence of detachment in North China Basin. Chinese J. Geophys. (in Chinese), 1994, 37(5) : 613--619
3 梅世蓉.邢台地震孕育发生模型及其前兆机理探讨.地震,1999． 19(1) ,1-10 MEI Shi-Rong. Model of preparation and generation of Xingtai earthquake and mechanism of its precursors. Earthquake (in Chinese), 1999,19(1) : 1--10
4 尹京苑,梅世蓉.薛艳.邢台地震区地壳速度结构特征与强震孕育发生关系的探索.地球物理学报,1999,42(5) :629-639 YIN Jing-Yuan, MEI Shi-Rong, XUE Yan. Relationship between the deep crustal features in velocity structure and the preparation of strong erathquakes in Xingtai area. Chinese J. Geophys. (in Chinese), 1999, 42(5) :629--639
5 河北省地震局.一九六六年邢台地震.地震出版社,1986,158-164 Seismic Bureau of Hebei. The 1966 Xingtai Earthquake. Beijing: Seismological Press, 1986, 158--164
6 国家地震局“一九七六年唐山地震编辑组”编.一九七六年唐山地震.北京:地震出版社,1982,103-121 Editorial Group for the 1976 Tangshan earthquake, State Seismological Bureau. The 1976 Tangshan Earthquake (in Chinese). Beijing: Seismological Press, 1982． 103--121
7 卢造勋,刘国栋,魏梦华.中国辽南地区地壳上地幔介质横向不均匀性与海城7． 3级地震.地震学报,1990,12(4) :367-378 LU Zao-Xun, LIU Guo-Dong, WEI Meng-Hua. Lateral inhomogeneity of crust and upper mantle in south l.iaoning, China and its relationship with the M7． 3 Haicheng earthquake. Acta Seismologica Sinica (in Chinese), 1990, 12(4) :367--378
8 滕吉文,王国正,刘道洪等.华北平原中部地区深部构造背景及邢台地震(二).地球物理学报,1975,18(3) :196-207 TENG Ji-Wen, WANG Guo-Zheng, LIU Dao-Hong, et al. Crustal structure of the central part of the North China plain and the Xingtai earthquake (Ⅱ). Chinese J. Geophys. (in Chinese), 1975, 18(3) : 196--207
9 孙武城.李松林.杨玉春.华北东部地区地壳结构的初步研究.地震地质,1985,7(3) :1-11 SUN Wu-Cheng, LI Song-Lin. YANG Yu-Chun. Preliminary study on crustal structures in the east of North China.Seismology and Geology (in Chinese), 1985, 7(3) : 1--11
10 孙武城,李松林,张晓普.华北大陆地壳.上地幔波浪断裂型构造的光弹模拟实验.华北地震科学,1983,1(1) :21-27 SUN Wu-Cheng, LI Song-Lin, ZHANG Xiao-Pu. Photoelastic test for simulating the undulate offset struture of crust and upper mantle in the North China. North China Earthquake Sciences (in Chinese), 1983． 1(1) : 21--27
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