Three-Dimensional Tomography of the Crust and Uppermost Mantle of Eastern Nepal

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

The continent-continent collision of the Indian Plate with southern Eurasia has produced the highest mountains -- the Himalaya -- and the largest and highest plateau -- Tibet -- on Earth today. The youthful nature of the Himalayan orogen makes it the paramount locality for studying mountain-building, and studies of the Himalaya have shaped much of what is known about the rheology of the continental lithosphere We build a high-resolution wavespeed models of eastern Nepal using data from ~200 seismic stations extending from western Nepal to the Indian state of Sikkim. We employ an inversion procedure that simultaneously models absolute local and regional earthquake P and S arrival times, relative teleseismic arrival times and surface wave group delay times from ambient noise and regional earthquakes to obtain 3-D velocity structure beneath the region. Including local earthquake allows for higher-resolution imaging of structure, as both the higher frequency content of local earthquake seismograms and the presence of the earthquake sources within the model volume generally allow for finer spatial sampling. A key feature of the inversion procedure is that the travel times are generated using a finite difference solution to the eikonal equation providing increased accuracy in the highly heterogeneous medium expected for the Himalaya. The teleseismic body waves recorded by large aperture seismic arrays allow illumination of the deeper structure of the mantle. The earthquakes within the volume are relocated in the heterogeneous structure Much of the seismicity is clustered to the west of Kathmandu at depths < 30 km. There is a clear image of the Main Himalayan thrust extending from a depth of ~5 km beneath the Himalayan foothills to ~12 km depth beneath the Lesser Himalaya. Small areas of strong fast wavespeeds exist in the center of the region in the upper 30 km of the crust. At depths of 40-50 km, large areas of slow wavespeeds are present which track along the plate boundary.

Presenting Author: Tak Ho

Authors