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

by Malay Mukul, Sridevi Jade, Kutubuddin Ansari, Abdul Matin and Varun Joshi

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.


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