The 2016Mw 6.7 Imphal Earthquake in the Indo‐Burman Range: A Case of Continuing Intraplate Deformation within the Subducted Slab

Abstract

The 2016 M-w 6.7 Imphal earthquake is one of the largest and instrumentally well-recorded seismic events to have occurred on the segment of the Indo-Burman plate boundary, where Indian and Burman plates converge in a roughly northeast direction (similar to 3-4 cm/yr). This segment of the plate boundary has not generated any great earthquakes in the documented history but is noted for its complex intraslab deformation, arc-parallel compression, and slip partitioning with the continental strike-slip Sagaing fault. Previous studies have noted a mix of faulting styles and hypocentral distribution, indicating the inherent complexities within this segment. Based on the teleseismic moment inversion of 88 P and SH waveforms from 70 global broadband seismic stations, we use the source model of the 2016 earthquake to corroborate the continuing intraslab deformation. The earthquake is sourced at a depth of 55 km, where the dip of the slab changes to similar to 50 degrees with the P axis oriented in the north-northeast-south-southwest direction. Our analysis of azimuths and plunges of P axes of 214 earthquakes (M-w >= 4: 5, Global Centroid Moment Tensor) is consistent with this trend. Previous studies have noted two distinct types of intraplate earthquakes along this segment: shallower events (25-75 km) due to arc-parallel bending and the deeper ones (90-150 km) in response to slab pull. Interplate seismicity is almost absent, and the potential for great earthquakes seems much lower compared with the rest of the eastern India plate boundary.