Seismicity and tectonics in south China and Burma

Abstract

A seismicity map of southwest-south China, eastern Burma and adjoining areas lying between latitudes 19° and 35°N, and between longitudes 91° and 108° E for the period 1900–1975 (except the period 1952–1954) is presented using all available data. The relationship between seismicity and tectonics of the area has been studied. On the basis of analysis it is suggested that the seismicity in the region is well-defined by several arcuate fracture belts surrounding the Assam wedge. Intense seismic activity is observed along the Burmese arc, Assam wedge, Hengtuan ranges, Kang Ting and Red River faults, Kang Tien ranges and western Szechwan province. Twenty-five new focal mechanism solutions for earthquakes in south China and the adjoining areas have been determined. These, in conjunction with the results obtained through earlier studies, suggest the dominance of thrust and normal faulting in the Burmese arc as well as in the Himalayan region, while normal faulting predominates in the mountainous regions in south China. The Kang Ting and Red River faults are mostly associated with strike-slip faulting. The results indicate that in Burma, the seismic slip vectors are directed towards the east from the Arakan-Yoma side and towards the west from the Shan plateau side, thus creating a V-shaped seismic zone underlying the Irrawaddy plains. Focal mechanism solutions of Himalayan earthquakes located north as well as south of the Indus suture zone indicate that the Indian plate is underthrusting the Tibetan plateau towards the north, whereas the latter is underthrusting the Indian plate towards the south. It further appears that following the convergence of the Indian and the Eurasian plates, the Tibetan and surrounding landmass is moving east to southeast. This, in turn, seems to create strike-slip faulting along giant faults in eastern Tibet and south China.