Investigation of past earthquakes in the Kopili fault zone, NE India: new evidence of paleoliquefaction

Abstract

The Kopili fault (KF) zone, one of the active faults in northeastern region (NER), has experienced large earthquakes in 1869 (Mw 7.4) and 1943 (Mw 7.2). In order to mitigate future occurrences of earthquakes in the KF, it is essential to understand its long-term seismic history and seismic hazard implications. Seismogenic liquefaction features were identifed at three trench sites in the foodplain deposits of Kolong River, near KF. The liquefaction features include multiple sand dykes and sand sills and are direct response to liquefaction of saturated sediment induced during past seismic activity. A total of seven samples from marker horizons have been processed to constrain the chronology of liquefaction features using optically stimulated luminescence (OSL) dating technique. OSL age constraints from Trench 1 indicate two episodes of earthquake-induced liquefaction since perhaps AD 1692, one, possibly two episodes of liquefaction in Trench 2 since AD 1540 and Trench 3, suggest one liquefaction event during the past 1000–2000 years. From the present study, given the limited results of the dating available we can conclude that two earthquakes induced liquefaction in the vicinity of the Kopili fault zone during the past~480 years. Additional excavations and dating of earthquake-induced liquefaction features are required to precisely evaluate the frequency of major earthquakes in the KF zone.