1995年7月20日河北沙城M_(L)4.1地震序列破裂过程中应力变化的研究

VARIATION OF STRESS DURING THE RUPTURE PROCESS OF THE 1995 M_L=4.1 SHACHENG, HEBEI, CHINA, EARTHQUAKE SEQUENCE

根据地震破裂动力学,研究了1995年7月20日河北沙城ML4.1地震序列破裂过程中,视应力和静态应力降与动态应力降之差的变化.结果表明,主震的视应力约为5MPa,而余震的视应力平均约为0.047MPa.在破裂过程中,主震的动态应力降大约为静态应力降的1.6倍,其差值约为2.7MPa;余震的动态应力降一致小于静态应力降,其差值平均约为-0.75MPa.因此,主震发生时,最终应力大于动摩擦应力,与断层突然锁住的模式相符;余震发生时,最终应力小于动摩擦应力,与地震断层错动过头的模式相符.因此,主震和余震的发生过程是有差别的.

According to the rupture dynamics of earthquakes, variations of the apparent stress and the difference between the static stress drop and the dynamic stress drop during the rupture of earthquakes are analyzed for the July 20, 1995 M_L=4.1 Shacheng, Hebei, China, earthquake sequence. Results obtained show that the apparent stress for mainshock is about 5 MPa, and the average apparent stress for aftershocks 0.047 MPa. During the rupture of the mainshock, the dynamic stress drop is approximately 1.6 times greater than the static stress drop with the difference of nearly 2.7 MPa. The dynamic stress drop is less than the static stress drop for all aftershocks with the average difference of -0.75 MPa. Therefore, when the mainshock occurs the final stress on the focal fault is higher than the dynamic frictional stress, corresponding to that the fault is abruptly locked. When the aftershocks occur the final stress on the focal fault is lower than the dynamic frictional stress, corresponding to that the fault overshoots. It can be seen from the above results that there could be some differences in the physic processes between the mainshock and the aftershocks.