Abstract:

In this paper, we analyze a sequence of small to moderate magnitude (ML = 1,2÷4,3) earthquakes occurred during January - February, 2018 in the Dien Bien Dong district, Dien Bien province, northwest region of Vietnam. The events are recored by broadband seismic stations that provide high quality data for hypocenter locations and focal - mechanism solutions. The routine locations of the earthquakes show that the epicentres fall close to the intersection between northwest - southeast trending Chieng Khuong fault and the semi - longitudinal fault system. The Double Difference (DD) method intergrated in HypoDD program (Waldhauser and Ellsworth, 2000) is applied to relocate three bigger events (ML = 4,3; 4,1 and 3,8). The relocations show that their epicenters moved to the southeast of the Chieng Khuong fault. Focal mechanism solutions are determined by the Moment tensor inversion method (Herrmann et al, 2011). The mechanisms of the three events show primarily strike - slip with normal faulting. The P - axis trends approximately northwest - southest. The geological investigations reveals that the Chieng Khuong fault is a right - leteral strike - slip fault (N216 - 2310) and dipping at 53o - 73 o southwest, which is conformable to the focal mechanism solutions. These results comfirm that the current seimic network in the Northwest region of Vietnam can ability obserb all M > 3,5 earthquakes with high accuracy of location, that could be use to study the morphology and mechanism of the faults that generating the earthquakes.