Structural insights from geodetic Global Positioning System measurements in the Darjiling-Sikkim Himalaya

Deformation in active convergent wedges like the Himalaya occurs over different time and space scales requiring integrated datasets for holistic insights into wedge-scale deformation. A new long-time series (1998-2009) of geodetic, static Global Positioning System (GPS) dataset suggests that active deformation in the Darjiling-Sikkim Himalaya (DSH) is not confined to the Himalayan front as previously believed. Instead, the ∼9 mm/yr N-S active convergence here is divided almost equally within the Lesser Himalayan Duplex (LHD) and the Higher Himalaya due to aseismic reverse slip of ∼18 mm/yr on the Himalayan décollement (Main Himalayan thrust (MHT)) dipping 6° → 006° and locked at ∼16 km depth. Slip transfer along the MHT causes minor to moderate earthquakes at the brittle-ductile transition in the DSH. Measured East velocities show no systematic variation indicating that strike-slip seismicity, though dominant in the region, does not alleviate the décollement (MHT) seismic hazard. Continued slip along the MHT, therefore, will cause a great décollement earthquake in the region. Also, GPS velocities vary in the eastern and western DSH suggesting segmentation of the Himalayan arc along a transverse fault over geological to decadal time scales. Our integrated approach can provide better insight into active deformation in convergent wedges worldwide.