GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 - POSTER GNGTS 2023 Crustal structure and discontinuities beneath the Nepal Himalaya using seismic ambient noise and teleseismic P wave coda autocorrelation Hari Ram Thapa 1-2 , Surya Pachhai 3 , Abdelkrim Aoudia 1 , Daniel Manu-Marfo 1 , Keith Priestley 4 , Supriyo Mitra 5 1 The Abdus Salam International Center for Theoretical Physics, Trieste, Italy 2 University of Trieste, Piazzale Europa, 1, 34127 Trieste TS 3 Department of Geology and Geophysics, The University of Utah, 201 Presidents' Cir, Salt Lake City, UT 84112, United States 4 University of Cambridge, The Old Schools, Trinity Ln, Cambridge CB2 1TN, United Kingdom. 5 India Institute of Science Education and Research (IISER) Kolkata, India Nepal is an actively deforming region due to its tectonic setting that hosts many destructive earthquakes including the most recent 2015 Gorkha earthquake of magnitude 7.8. 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, we need highly resolved 3-D structure of the crust. This study presents a new high-resolution 3-D shear (S) -wave velocity structure of the crust beneath Himalaya Nepal using dispersions obtained from the ambient noise. Our results show significant differences in the crustal structure within the region and correlate well with known geological and tectonic features present there. The results from the autocorrelation of teleseismic P coda indicate four major seismic discontinuities in the crust: depth of sediments deposit, top of subducting Indian crust, interface between upper and lower Indian crust, and Moho. The S-velocity profile indicates the duplex structure in the Main Himalayan Thrust beneath Lesser Himalaya and low velocity zone down to 20-30 km right to north of the coseismic rupture of 2015 Gorkha earthquake. The low velocity zone beneath High Himalaya is located where GPS data show interseismic creeping. This low velocity zone is further connected to another very low velocity zone beneath South Tibet by the newly identified downdip ramp towards north. Keywords : Himalaya Nepal, Ambient Noise, Surface Wave Tomography, Bayesian Inversion, 3-D shear wave structure, duplex structure Corresponding author: hthapa@ictp.it