Evidence of the 1950 Great Assam Earthquake Surface Break Along the Mishmi Thrust at Namche Barwa Himalayan Syntaxis

Abstract

Paleoseismological trenching at Kamlang Nagar along the Mishmi Thrust in the Eastern Himalayan Syntaxis, aided by radiocarbon analyses of charcoals yielding ages of 1111–914 B.C. to A.D. 1761–1968 infer primary evidences of co-seismic surface faulting. Correlation with results of an earlier paleoseismological study indicates two successive surface rupturing earthquakes at ∼1800-years interval, the most recent event very likely corresponding to the 1950 Assam earthquake (Mw 8.6). A dip-slip displacement of 24.6 ± 4.6 m was estimated along a 25 ± 5°E dipping fault during the 1950 earthquake. Our study suggests dual surface faulting by the 1950 event along two orthogonal fault systems, that is, the Himalayan Frontal Thrust and the Mishmi Thrust. It thus emphasizes that, the seismicity pattern in the Mishmi Range where the locked zone of the Main Himalayan Thrust extends beyond the suture zone, is unlike that of the western and central Himalaya. © 2021. American Geophysical Union. All Rights Reserved.