tailieunhanh - Báo cáo "Spatial variation of the active stress field in the North West of Vietnam: implication for related geohazard mitigation "

The NW of Vietnam is currently affected by a stress field characterizing by approximatc1y NS and EW sub-horizontal maximum and minimum principal stress axis respective1y. The results obtained from field investigations and numeric modelisation reveal that the present stress field varies not only in relative magnitude but also in orientation of principal stress axes from point to point and in depth. The tectonic stress variation strong1y depends on the geometry and active kinematics of faults as well as on their earthquake history. . | VNU Journal of Science Earth Sciences 25 2009 56-63 Spatial variation of the active stress field in the North West of Vietnam implication for related geohazard mitigation Nguyen Van Vuong1 Vu Van Tích1 Ta Trong Thang1 Bui Van Duan2 1 College of Science VNU 2Institute of Geophysics Vietnam Academy of Science and Technology Received 4 January 2009 received in revised form 21 January 2009 Abstract. The NW of Vietnam is currently affected by a stress field characterizing by approximately NS and EW sub-horizontal maximum and minimum principal stress axis respectively. The results obtained from field investigations and numeric modelisation reveal that the present stress field varies not only in relative magnitude but also in orientation of principal stress axes from point to point and in depth. The tectonic stress variation strongly depends on the geometry and active kinematics of faults as well as on their earthquake history. The modeling shows that the tectonic stress field tends to simplify from the subsurface downward to 40km depth. At this level depth the stress concentrates along the Dion Bien-Lai Chau fault while other faults release stress. Horizontally die liigh tectonic stress accumulates in some area such as western side of the Dien Bien-Lai Chau fault tire area from Dien Bien Dong to Lai Chau along the Son La Song Ma faults and in some segments of Song Ca fault. These stress anomalies link closely to historic earthquakes. Keywords Stress field Geohazard Active tectonics Geodymanics Earthquake. 1. Introduction The NW of Vietnam is limited to the north east and to the east by the Red River fault system to the south by the Song Ca fault to the west by the Dien Bien-Lai Chau fault. The whole region is sliced by NW-SE trending faults net that inherited from the Indosinian shear zones 4 . Most of them are active as sinistral strike slip faults dining Late Oligocene to Middle Miocene and subsequent dextral strike slip in Late Pliocene up to presence. Corresponding .