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Mw 6.7 earthquake hits Manipur state, India
In the early morning hours of 4th January 2016, a moderate Mw 6.7 earthquake struck the mountainous state of Manipur in northeastern India, close to the Indo-Myanmar border. Reports from local and international press agencies cite the earthquake as the cause of numerous fatalities, hundreds of injuries and structural damage in northeastern India and in adjacent parts of Bangladesh. Shaking was felt throughout Bangladesh, in parts of Tibet and eastern Nepal, more than 1000 kilometres away from the epicentre of this earthquake. It was strong enough to rouse people from their slumber in Kolkata and Ranchi in eastern India, and was also felt on the upper floors of buildings as far south as Yangon, Myanmar.
The size of Monday’s earthquake is far smaller than the Mw 7.8 earthquake on 25 April 2015 that struck Gorkha, Nepal, which caused more than 8,000 fatalities in the Nepal Himalayas. The seismic moment released by the earthquake in Manipur on Monday morning is about 40 times smaller than the Gorkha earthquake, and about 10 to 16 times greater than the Mw 6.0 Mt. Kinabalu earthquake that took place last June in the Sabah province of eastern Malaysia.
Similar to the Nepal quake, the Manipur earthquake resulted from the northeastward motion of the Indian plate, but at the Indian plate’s eastern margin instead of the Himalayan mountain range. The estimated hypocentre from the global seismic network suggests that this earthquake was a moderate-depth earthquake that occurred within the subducted Indian plate beneath the northern Indo-Burman Ranges.
Historical events in the Manipur region with similar spatial macroseismic or “felt” extents have occurred previously, including an earthquake in the late 1800’s and another in May 1939. The 10 January 1869 Cachar earthquake that produced intensities in excess of EMS 7 in the Manipur Valley is the most damaging earthquake in the region in the last 150 years. Recent instrumented earthquakes such as the Mw 7.3 Indo-Myanmar earthquake on 6 August 1988 nucleated at a greater depth and farther to the east.
Although the rupture that produced this earthquake was not as shallow as the 2015 Mt. Kinabalu earthquake and the 2015 Gorkha earthquake, its close proximity to the sediment-filled Imphal Basin could have generated strong ground motions in Imphal and the rest of the Manipur Valley. The strong shaking may have also triggered hazardous landslides on the steep slopes of the northern Indo-Burman Ranges that could have resulted in additional damage in this mountainous area.
Cover image via United States Geological Survey