No abstract

Myanmar, one of the most active tectonic regions in the world, endures the risk of destructive earthquakes. Based on seismic data recorded at the recently deployed dense array of the China-Myanmar Geophysical Survey in the Myanmar Orogen (CMGSMO), we detect 854 and locate 599 shallow earthquakes with high precision and determine the focal mechanisms of 40 earthquakes. We identify two NW-SE trending fault zones accommodating dextral strike-slip earthquakes beneath the Central Basin, indicating potential seismic risk in the region. We also recognize a nearly N-S trending seismic zone in the overlying Indo-Burma Ranges (IBR) crust near the Kabaw Fault (KBF). The earthquakes within this seismic zone mostly show thrusting focal mechanisms. Our results suggest that strike-slip deformation dominates to the east of the KBF, while shortening is mainly confined to the west of the KBF in Central Myanmar.Plain Language Summary Myanmar in Southeast Asia suffers from disasters resulting from destructive earthquakes. However, the present knowledge on their causative faults is limited due to the deployment of few seismic observation stations in Myanmar. We deployed a seismic observation network containing 71 stations for 1.5 years and tried to identify unknown causative faults and their characteristics by studying the small earthquakes there. Our results suggest that larger areas than previously expected in Myanmar may encounter significant seismic hazards. More attention to mitigating hazards should be paid to the Central Basin and western mountain areas, where densely populated cities are located.

Indian continental subduction can explain Cenozoic crustal deformation, magmatic activity and uplift of the Tibetan Plateau following the India-Asia collision. In the western Himalayan syntaxis and central Himalaya, subduction or underthrusting of the Indian Plate beneath the Eurasian Plate is well known from seismological studies. However, because information on the deep structure of the eastern Himalayan syntaxis is lacking, the nature of the Indian subduction slab beneath Myanmar and the related tectonic regime remain unclear. Here, we use receiver function common conversion point imaging from a densely spaced seismic array to detect direct structural evidence of present-day Indian continental subduction beneath Asia. The entire subducting Indian crust has an average crustal thickness of~30 km, dips at an angle of~19°, and extends to a depth of 100 km under central Myanmar. These results reveal a unique continental subduction regime as a result of Indian-Eurasian continental collision and lateral extrusion.