3 Jan 2016: Quake Insight
The Imphal, India earthquake struck at 55-60 km (30-36 mi) depth. Its great depth will reduce its impact on the many poorly built homes, factories, and offices in the region. Nevertheless, 224,000 people live in Imphal, where the shaking intensity predicted by the USGS PAGER system is very strong. The earthquake is the product of India’s 40 million year-long collision into Tibet, with the Indian subcontinent hurtling northward at a speed of 50 mm/yr (2”/yr), uplifting the Himalayas, deforming Southeast Asia, and extruding the crust to the northeast. The focal mechanism indicates a combination of strike-slip and thrust motion, which is characteristic of the extrusion process. The Imphal, India earthquake was preceded by a M=4 quake 22 days ago about 150 km (100 mi) to the east (see the map below); the two quakes are probably unrelated.
The past century of earthquakes shows that this region has been the site of numerous damaging events, including two M=8 events, including the 1950 M=8 Assam quake 300 mi (500 km) to the north, and a M=8 quake 200 km (130 mi) to the east. Depths of 50 km are common (green dots below) in the vicinity of today’s quake.
Focusing on M≥7.5 quakes over the past millennium, the map from Bilham (Science, 2013) below shows that the Great 1897 M=8 Shillong quake struck within 100 km (60 mi) to the west, and a series of M~7.5 shocks struck in the 1800’s along the north-oriented band of which this shock is a part.
Ross Stein and Volkan Sevilgen, Temblor
Data from USGS, ISC-GEM Seismic Catalog, and Bilham (2013)