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The Main Himalayan Thrust beneath Nepal and Southern Tibet illuminated by seismic ambient noise and teleseismic P wave coda autocorrelation
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  • Hari Ram Thapa,
  • Surya Pachhai,
  • Abdelkrim Aoudia,
  • Daniel Manu-marfo,
  • Keith F. Priestley,
  • Supriyo Mitra
Hari Ram Thapa
The Abdus Salam International Center for Theoretical Physics (ICTP)

Corresponding Author:hthapa@ictp.it

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Surya Pachhai
University of Utah
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Abdelkrim Aoudia
International Centre for Theoretical Physics
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Daniel Manu-marfo
International Centre for Theoretical Physics
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Keith F. Priestley
University of Cambridge
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Supriyo Mitra
Indian Institute of Science Education and Research Kolkata
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Nepal is an actively deforming region due to its tectonic setting that hosts many destructive earthquakes including the recent 2015 Mw 7.8 Gorkha earthquake. To better understand the physics of earthquakes and their precise location as well as monitoring of seismicity and real-time seismic hazard in the region, a highly resolved 3-D structure of the crust is essential. This study presents a new 3-D S-wave velocity structure of the crust using ambient noise tomography (ANT). This study further constrains the discontinuities beneath Himalaya Nepal using teleseismic P-wave coda autocorrelation. The results from the P-wave coda autocorrelation identify major seismic discontinuities in the crust including the Main Himalayan Thrust (MHT). The MHT with two ramps correlates well with a low S-wave velocity layer obtained from the ANT. The first ramp agrees with the duplex structure in the MHT beneath Lesser Himalaya while the second connects flat low velocity beneath High Himalaya to a broad low-velocity zone beneath South Tibet. The geometry and extent of the High Himalaya low-velocity layer mimics the decollement coupling zone inferred from GPS data with widths of 50-70 km north of the nucleation of the 2015 Mw 7.8 Gorkha earthquake and 90-100 km north of the source of the Mw 8.4 1934 earthquake. The occurrence of millenary Mw>9.0 earthquakes in Central and Eastern Nepal would require either a wider coupling low velocity zone compared to the ones identified in this work or the involvement of southernmost Tibet low velocity decoupling zone so to store enough elastic energy.
09 Jan 2023Submitted to ESS Open Archive
10 Jan 2023Published in ESS Open Archive