Crustal structure beneath Nepal using Bayesian inversion of receiver functions and surface-wave dispersions
Abstract
The detailed-crustal velocity structure beneath Nepal Himalayas allows us to better understand the tectonic processes and improve the earthquake location and seismic hazard evaluation for the region. Previous studies suggest an anisotropic Main-Himalayan Thrust (MHT) beneath Nepal based on conversions of direct P-waves coming from different backazimuths and distant earthquakes (teleseismic receiver functions). However, proper quantification of isotropic/anisotropic velocity and dipping of MHT and their uncertainties become challenging due to the trade-off between layer properties. Additionally, there are limited studies on the extensive-crustal structures beneath Nepal. We recently developed a Bayesian inversion of both radial and transverse receiver functions and here applied it to data from narrow backazimuth and epicentral distance ranges recorded on more than 30 temporary seismic stations in Nepal. The inversion results for the stations near the southern edge of the Himalayan front (main-frontal thrust) show a strong anisotropic layer ( 35±5%) with high dip ( 20±5°) between a very slow-velocity shallow layer above and a fast-velocity deeper layer below it. The anisotropic layer continues northward with low dip angles (5±2°) beneath the stations south of Kathmandu and high dip angles north of Kathmandu. This anisotropic layer may be due to the shearing motion between the northward moving Indian crust with respect to the overriding Himalayan crust. Our inversion further suggests a very high S-wave velocity and strong anisotropy in the top layer, particularly north of the thrust that separates high Himalaya from lesser Himalaya (main-central thrust). Here, we further focus on the inversion of receiver functions from different backazimuths and short-period surface-wave dispersions extracted from the noise. The surface wave dispersions remove the depth-velocity trade-offs and give strong constraints on the average S-wave velocity while the receiver functions from multiple backazimuths enable to better estimate the anisotropy.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.S43D0889P
- Keywords:
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- 7205 Continental crust;
- SEISMOLOGY;
- 8025 Mesoscopic fabrics;
- STRUCTURAL GEOLOGY;
- 8030 Microstructures;
- STRUCTURAL GEOLOGY;
- 8110 Continental tectonics: general;
- TECTONOPHYSICS