| 1975年2月4日辽宁省海城地震的震源机制 |
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| 引用本文： | 顾浩鼎,陈运泰,高祥林,赵毅.1975年2月4日辽宁省海城地震的震源机制[J].地球物理学报,1976,19(4):27-285. |
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| 作者姓名： | 顾浩鼎 陈运泰 高祥林 赵毅 |
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| 作者单位： | 1. 辽宁省地震局;
2. 中国科学院地球物理研究所;
3. 宁夏回族自治区地震队;
4. 国家地震局广州地震大队 |
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| 摘 要： | 由地震纵波初动符号的资料,求得了海城地震系列中Ms≥4.0的24个地震的断层面解。主震发生于1975年2月4日,它的一个节面走向N70°W,倾向NE,倾角81°;另一个节面走向N23°E,倾向SE,倾角75°。根据余震的空间分布以及地面形变资料选取N70°W的节面为断层面,主震是发生在这个近乎直立的断层面上的左旋走向滑动,略具正的倾向滑动分量。前震及大多数余震的震源机制和主震的相似,有四个Ms≥4.0的余震的震源机制和主震的迥然不同,表现出滑动向量和主震的滑动向量相反的断层错动方式。这种情况的一种可能的解释是主震时在断层的一些地段发生错动过头。 由野外资料及余震的空间分布资料计算了主震的震源参数。主震断层长70公里,宽20公里,平均错距45厘米,地震矩2.1×1026达因·厘米,应力降4.8巴,应变降7.3×10-6。它是发生在不能积累起较高应力的薄弱地带的一次低应力降的地震。 由地震纵波初动的半周期和振幅的资料计算了81个前震和余震的震源尺度、地震矩、应力降和平均错距。结果表明前震和余震的应力降都比较低,一般在0.1-1巴之间。余震区中有两个应力降相对说来比较高（高于0.8巴）的地区,它们恰好对应于主破裂错动过头的部位。这些结果意味着震前高应力、错动过头、相对高应力降和震源机制反向四者之间
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| 关 键 词： | 余震 主震 海城地震 断层面解 震源机制 前震 应力降 节面 邢台地震 初动 |
FOCAL MECHANISM OF HAICHENG,LIAONING PROVINCE,EARTHQUAKE OF FEBRUARY 4, 1975 |
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| GU HAO-DING,CHEN YUN-TAI,GAO XIANG-LIN,ZHAO YI.FOCAL MECHANISM OF HAICHENG,LIAONING PROVINCE,EARTHQUAKE OF FEBRUARY 4, 1975[J].Chinese Journal of Geophysics,1976,19(4):27-285. |
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| Authors: | GU HAO-DING CHEN YUN-TAI GAO XIANG-LIN ZHAO YI |
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| Institution: | 1. The Seismological Bureau of Liaoning Province;
2. Institute of Geophysics, Aeademia Sinica;
3. The Seismological Brigade of the Ningxia, Hui Nationality Autonomous Region ;
4. The Seismological Brigade of Guangzhou, National Seismological Bureau |
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| Abstract: | Fault plane solutions are obtained from data of the first motions for 24 earthquakes with Ms ≥ 4.0 of the Haicheng earthquake sequence, the mainshock of which occurred on Feb. 4, 1975. One of the nodal planes of the mainshock strikes N 70° W, dipping 80° to the NE. while the other nodal plane strikes N 23° B, dipping 75° to the SE. Based on the data of the spatial distributions of the after shocks and the ground deformations, the N 70° W nodal plane is taken as the fault plane. The faulting is nearly a vertical, left-lateral strike-slip with a minor component of normal dip-slip movement. While the focal mechanisms of all the fore-shocks and most of the aftershocks are similar to that of the mainshock, those of 4 aftershocks with Ms ≥ 4.0 are remarkably different from the mainshock. They represent a faulting with slip vector reversed in direction to that of the mainshock. One possible explanation for these exceptions is that during the mainshock the fault movement overshot along some segments of the fault.The source parameters of the mainshock are calculated from the data of field observations and spatial distributions of the aftershocks. The fault length, width, averge dislocation, seismic moment, and stress-drop, of the mainshock, are estimated as 70 km, 20km, 45cm, 2.1 x 1026 dyne·cm, 4.8 bars, respectively. It is a low stress-drop earthquake occurring in a weak zone that is incapable of accumulating higher stresses.For 81 foreshocks and aftershocks the source dimensions, seismic moments, stress-drops as well as average dislocations are calculated from the data of the first half cycles and amplitudes of the seismic P-waves. The results indicate that the stress-drops are rather low, and generally in the range of 0.1-1.0 bars, for both the foreshocks and aftershocks. There are two regions with relatively higher stress-drops （ ≥ 0.8 bars）, which correspond to the overshooting portions on the main fracture. These results imply that there might be some intrinsic connections between higher initial stresses before the mainshock, overshooting of fault movment, relatively higher stress-drops, and reverse of the slip vectors of focal mechanisms. It seems that the latter three phenomena are the results of the relatively higher initial stress. |
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