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Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal

Lavé, J. and Avouac, J. P. (2000) Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal. Journal of Geophysical Research B, 105 (B3). pp. 5735-5770. ISSN 0148-0227. doi:10.1029/1999JB900292.

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We analyze geomorphic evidence of recent crustal deformation in the sub-Himalaya of central Nepal, south of the Kathmandu Basin. The Main Frontal Thrust fault (MFT), which marks the southern edge of the sub-Himalayan fold belt, is the only active structure in that area. Active fault bend folding at the MFT is quantified from structural geology and fluvial terraces along the Bagmati and Bakeya Rivers. Two major and two minor strath terraces are recognized and dated to be 9.2, 2.2, and 6.2, 3.7 calibrated (cal) kyr old, respectively. Rock uplift of up to 1.5 cm/yr is derived from river incision, accounting for sedimentation in the Gangetic plain and channel geometry changes. Rock uplift profiles are found to correlate with bedding dip angles, as expected in fault bend folding. It implies that thrusting along the MFT has absorbed 21 ± 1.5 mm/yr of N-S shortening on average over the Holocene period. The ±1.5 mm/yr defines the 68% confidence interval and accounts for uncertainties in age, elevation measurements, initial geometry of the deformed terraces, and seismic cycle. At the longitude of Kathmandu, localized thrusting along the Main Frontal Thrust fault must absorb most of the shortening across the Himalaya. By contrast, microseismicity and geodetic monitoring over the last decade suggest that interseismic strain is accumulating beneath the High Himalaya, 50–100 km north of the active fold zone, where the Main Himalayan Thrust (MHT) fault roots into a ductile décollement beneath southern Tibet. In the interseismic period the MHT is locked, and elastic deformation accumulates until being released by large (M_w > 8) earthquakes. These earthquakes break the MHT up to the near surface at the front of the Himalayan foothills and result in incremental activation of the MFT.

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Avouac, J. P.0000-0002-3060-8442
Additional Information:© 2000 by the American Geophysical Union. Received 1 December 1998; accepted 20 August 1999; published 10 March 2000. We are most grateful to M. R. Pandey, Tandukar and the National Seismological Center (DMG, Kathmandu) for the help in the organization of the field surveys. The Petroleum Project kindly provided access to their seismic profiles. Remote sensing DMG team kindly provided a draft of the sheet covering the surveyed area of the 1:100,000 geological map of Nepal in advance of publication. Francis Guillois and Pascal Benoit have drawn some of the figures. We are indebted to R. Weldon and D. Fisher and to B. Anderson and A. Densmore, who provided thoughtful reviews that led us to significant modifications of the two companion manuscripts that were initially prepared. We are grateful to A. Densmore, D. Granger, and M. Ellis for thoughtful reviews and comments on the present version of the manuscript. We also benefited from comments by Peter Molnar and Paul Tapponnier on an early draft and by Niels Hovius on the modified version.
Group:Seismological Laboratory
Issue or Number:B3
Record Number:CaltechAUTHORS:20120906-154655223
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Official Citation:Lavé, J., and J. P. Avouac (2000), Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal, J. Geophys. Res., 105(B3), 5735–5770, doi:10.1029/1999JB900292
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33917
Deposited By: Tony Diaz
Deposited On:07 Sep 2012 16:36
Last Modified:09 Nov 2021 23:05

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