The 2020 Mw 5.5 Mizoram earthquake and associated swarm activity in the junction of the Surma Basin and Indo-Myanmar Subduction Region

A severely felt earthquake of Mw 5.5 occurred on 22 June 2020, in the Champhai district of Mizoram, North East Region (NER) of India, in the vicinity of the Indo-Myanmar subduction zone. This earthquake was associated with a swarm type of activity; six earthquakes of Mw 4.0–5.1 and some 16 earthquakes of Mw 3.0–3.9 occurred almost within two months like a swarm which caused much panic in the Mizoram state and neighbouring region. The mainshock of Mw 5.5 was preceded by an earthquake of Mw 5.1 on the previous day, 21 June 2020, in the capital city Aizawl, ~ 70 km northwest of Champhai. All of these events originated at shallow depth (~ 10–30 km) and occurred in the intra-plate zone of the subducting Indian plate. Fault plane solution of the mainshock indicates strike-slip faulting that matches fairly well with the transverse Mat Fault in the Outer Indo-Burma Wedge (OIBW). Macroseismic investigation of the mainshock at some 46 sites shows the maximum intensity of VIII (MMI scale) at the epicentral track. An attenuation relation between intensity and hypocentral distance is derived, which may be helpful to assess seismic hazards in this region.