利用地震矩张量初步分析断裂带的运动学特征

PRELIMINARY ANALYSIS OF KINEMATIC FEATURES OF A FAULT ZONE BY SEISMIC MOMENT TENSORS

文中探讨了利用地震矩张量反演断裂形变带运动学参数的方法,并将其应用于鲜水河断裂带和汾渭断裂带现今运动学特征的研究。结果表明,鲜水河断裂带呈N16°W方向拉伸,N74°E方向压缩,并且以10.9mm/a的速率发生左旋剪切运动;汾渭断裂带呈N20°W方向拉伸,N78°E方向压缩,并且以0.24mm/a的速率发生右旋剪切运动。

In this paper, the method for inversing the kinematics parameters of a fault zone from seismic moment tensors is discussed and applied to the study of the present kinematics characteristics of Xianshuihe Fault zone and Fenwei Fault zone. The results show that the Xianshuihe Fault zone extends in the direction of N16°W and is compressed in the direction of N74°E. The average sinistral motion rate is about 10.9 mm/a. The Fenwei Fault zone extends in N20°W and is compressed in N78°W direction. The average dextral motion rate is about 0.24mm/a. Comparing the results mentioned above to the geological information and the GPS results, it is found that the motion directions of fracture zone are basically agreeable, .but the slip rate is less than that of the latter two, especially in the Fenwei Fault zone. Three reasons may explain this phenomenon, firstly, the time when the data are collected is different; secondly, all strain energy produced by geological body is assumed to be released by means of the stick slip, instead of creep-slip of the fault ; and thirdly there were totally 14 earthquakes of magnitude greater that 5 occurring in the sampled time period, among which there was only one earthquake of maximum over 6 and the largest event is M 6.2. The motion rate of the fault zone calculated from seismic moment tensors is less than the average rate drawn by geological information. This shows that the strain energy of the geological body has not been released completely. So there exists high seismic risk. In addition, the motion rate of the Fenwei Fault zone is less than that of the Xianshuihe Fault zone, indicating that the level of seismicity and the energy released by earthquake of the former is less than that of the latter.