Ader, Thomas and Avouac, Jean-Philippe and Liu-Zeng, Jing and Lyon-Caen, Hélène and Bollinger, Laurent and Galetzka, John and Genrich, Jeff and Thomas, Marion and Chanard, Kristel and Sapkota, Soma Nath and Rajaure, Sudhir and Shrestha, Prithvi and Ding, Lin and Flouzat, Mireille (2012) Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Himalayan Thrust: Implications for seismic hazard. Journal of Geophysical Research B, 117 . Art. No. B04403. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20120517-092256179
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We document geodetic strain across the Nepal Himalaya using GPS times series from 30 stations in Nepal and southern Tibet, in addition to previously published campaign GPS points and leveling data and determine the pattern of interseismic coupling on the Main Himalayan Thrust fault (MHT). The noise on the daily GPS positions is modeled as a combination of white and colored noise, in order to infer secular velocities at the stations with consistent uncertainties. We then locate the pole of rotation of the Indian plate in the ITRF 2005 reference frame at longitude = − 1.34° ± 3.31°, latitude = 51.4° ± 0.3° with an angular velocity of Ω = 0.5029 ± 0.0072°/Myr. The pattern of coupling on the MHT is computed on a fault dipping 10° to the north and whose strike roughly follows the arcuate shape of the Himalaya. The model indicates that the MHT is locked from the surface to a distance of approximately 100 km down dip, corresponding to a depth of 15 to 20 km. In map view, the transition zone between the locked portion of the MHT and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the Himalaya. According to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data, this transition seems to happen in a zone where the temperature reaches 350°C. The convergence between India and South Tibet proceeds at a rate of 17.8 ± 0.5 mm/yr in central and eastern Nepal and 20.5 ± 1 mm/yr in western Nepal. The moment deficit due to locking of the MHT in the interseismic period accrues at a rate of 6.6 ± 0.4 × 10^(19) Nm/yr on the MHT underneath Nepal. For comparison, the moment released by the seismicity over the past 500 years, including 14 M_W ≥ 7 earthquakes with moment magnitudes up to 8.5, amounts to only 0.9 × 10^(19) Nm/yr, indicating a large deficit of seismic slip over that period or very infrequent large slow slip events. No large slow slip event has been observed however over the 20 years covered by geodetic measurements in the Nepal Himalaya. We discuss the magnitude and return period of M > 8 earthquakes required to balance the long term slip budget on the MHT.
|Additional Information:||© 2012 American Geophysical Union. Received 1 December 2011; revised 20 February 2012; accepted 21 February 2012; published 13 April 2012. This project was supported by the Gordon and Betty Moore Foundation, through the Tectonics Observatory, NSF grant EAR0838495 and the China Geological Survey (1212011121265). We would like to thank reviewers Michael Taylor from the University of Kansas and Rebecca Bendick from the University of Montana for useful comments. We thank the staff of the NSC in Nepal for their hard work on the seismic network and the continuous GPS stations, and for providing us with the NSC seismic catalog for this study. We thank Michel Dandine and Dili Ram Tiwari for their contribution to the seismicity catalog of Nepal. We also thank Frederic Herman for providing values of his temperature models. This is Tectonic Observatory’s contribution 193.|
|Group:||Caltech Tectonics Observatory|
|Subject Keywords:||Himalaya interseismic coupling plate tectonics seismotectonics|
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|Official Citation:||Ader, T., et al. (2012), Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Himalayan Thrust: Implications for seismic hazard, J. Geophys. Res., 117, B04403, doi:10.1029/2011JB009071.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||18 May 2012 18:23|
|Last Modified:||26 Dec 2012 15:13|
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