NUMERICAL MODELING OF THE GENERATION PROCESS OF THE 1906 MANAS M_S7.7 EARTHQUAKE

Numerical modeling of the relationship between tectonic stress and seismicity is one of the important subjects in seismogeology. In this paper, the generation process of the 1906 Manas M S7 7 earthquake is simulated using finite element method on the basis of the integration of newly obtained geologic and geophysical data on this earthquake. The Manas strong earthquake region is composed of North Tianshan Mountain and South Marginal Depression of the Jungar basin separated by the South Marginal Fault of the basin. The tectonic deformation in this region is dominated by a thrust system developed at middle upper crustal level, thrusting over from the south to the north. The southern part of the thrust system, the North Tianshan Mountain, belongs to a thick skinned structure and the main detachment surface is located below the depth of brittle ductile transition. There are three major fault zones in the North Tianshan Mountain; they are the Boloholo Fault, the Yamate Fault and the South Marginal Fault of the Jungar basin. The tectonic deformation in the South marginal Depression of the Jungar basin is dominated mainly by the brittle deformation of the sedimentary cover. The South Marginal Fault of the Jungar basin is situated at the transition zone from thick skinned to thin skinned structures. This transition zone is also the brittle ductile transition zone, which has strong ability to store energy and hence is suitable for the generation of strong earthquake. The 1906 Manas M S7 7 earthquake just occurred on this tectonic zone. According to the tectonic framework of the Manas M S7 7 earthquake region, the distribution of tectonic stress in this region is simulated using three dimensional finite element method. The results show that the hypocenter of the Manas earthquake is just located at the position of stress concentration, and the stress here increases as time goes on. These results reveal also the process of stress accumulation at the hypocenter of the Manas strong earthquake, and would help to understand the generation process of the Manas M S7 7 earthquake.