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Modeling mountain building and the seismic cycle in the Himalaya of Nepal

Cattin, R. and Avouac, J. P. (2000) Modeling mountain building and the seismic cycle in the Himalaya of Nepal. Journal of Geophysical Research B, 105 (B6). pp. 13389-13407. ISSN 0148-0227. http://resolver.caltech.edu/CaltechAUTHORS:20120907-133541924

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Abstract

A host of information is now available regarding the geological and thermal structure as well as deformation rate across the Himalaya of central Nepal. These data are reconciled in a two-dimensional mechanical model that incorporates the rheological layering of the crust which depends on the local temperature and surface processes. Over geological timescale (5 Ma) the ∼20 mm/yr estimated shortening rate across the range is accommodated by localized thrust faulting along the Main Himalayan Thrust fault (MHT). The MHT reaches the surface along the foothills, where it is called the Main Frontal Thrust fault (MFT). The MHT flattens beneath the Lesser Himalaya and forms a midcrustal ramp at the front of the Higher Himalaya, consistent with the river incision and the anticlinal structure of the Lesser Himalaya. Farther northward the MHT roots into a subhorizontal shear zone that coincides with a midcrustal seismic reflector. Aseismic slip along this shear zone is accommodated in the interseismic period by elastic straining of the upper crust, increasing the Coulomb stress beneath the front of the Higher Himalaya, where most of the microseismic activity clusters. Negligible deformation of the hanging wall requires a low apparent friction coefficient (μ) less than ∼0.3 on the flat portion of the MHT. On the ramp, μ might be as high as 0.6. Sensitivity tests show that a rather compliant, quartz-rich rheology and a high radioactive heat production in the upper crust of ∼2.5 μW/m^3 is required. Erosion affects the thermal structure and interplays with crustal deformation. A dynamic equilibrium is obtained in which erosion balances tectonic uplift maintaining steady state thermal structure, topography, and deformation field. Using a linear diffusion model of erosion, we constrain the value of the mass diffusivity coefficient to 0.5–1.6×l0^4 m^2/yr. This study demonstrates that the data are internally consistent and compatible with current understanding of the mechanics of crustal deformation and highlight the role of viscous flow in the lower crust and of surface erosion in orogeny processes on the long term as well as during interseismic period.


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Additional Information:© 2000 American Geophysical Union. Received 21 April 1999; accepted 28 January 2000; published 10 June 2000. This modeling was built on previous results acquired in a collaborative program that has benefited from the contributions of J. Lavé, G. Burov, and of our Nepalese colleagues at the Department of Mines and Geology, in particular M. R. Pandey and R. P. Tandukar. Constructive reviews by S. H. Lamb, B. Parson, and R. Stein contributed to improving the manuscript. We are most grateful to P. Henry for computing the thermal structure used in this study and for fruitful discussions of our results, and we thank: J. Chéry for providing the finite element code ADELI.
Record Number:CaltechAUTHORS:20120907-133541924
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120907-133541924
Official Citation:Cattin, R., and J. P. Avouac (2000), Modeling mountain building and the seismic cycle in the Himalaya of Nepal, J. Geophys. Res., 105(B6), 13,389–13,407, doi:10.1029/2000JB900032.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33938
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:07 Sep 2012 20:58
Last Modified:26 Dec 2012 16:08

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