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Déformation Intersismique de l'Himalaya du Népal à partir de données GPS

Abstract : The velocity of interseismic convergence through the Nepal Himalaya - essential parameter in the study of the seismic cycle - is discussed since several years. To constrain this velocity, we have successfully combined geodetic data from campaign GPS surveys, cGPS stations and DORIS stations to determine the plate motion of India and contemporary crustal strain across Nepal Himalaya. The pattern of crustal deformation across the Eastern and Central Himalaya, implies
that the MHT is locked over a distance of about 115km from the surface to a depth of about 20km beneath the front of the mountain range. Horizontal shortening due to ductile creep along the deeper portion of the MHT appears to fall in the range 19+/-2.5mm/yr along strike in Central and Eastern Nepal. Small (<20% of the slip rate) lateral variations are suspected in that area but are not properly resolved due to the low spatial sampling of the area. Across Western Nepal, the pattern of deformation and the shortening rate, given to be around 13.4+/-5mm/yr, is less well constrained due to the lack of GPS stations.

The analysis of GPS time series showed, in addition to the secular term, important seasonal variations, in particular on the horizontal component perpendicular to the Himalayan range. We could highlight that these seasonal variations did not come from a processing artefact, but of the flexural response of the continental crust to an aquifer loading located in the Ganges basin. The flexural response to this seasonal load induced variations of Coulomb stress localised in the Himalayan midcrustal seismic swarm. These variations make it possible to explain in first order the seasonal variations seismicity
rate highlighted on the Nepalese seismicity catalogue.

The study of the grain sizes of quartz enabled us to determine the amplitude of the differential stress present around the brittle-ductile transition. From the combination of thermometric, structural, geodetic and paleopiezometric data, an experimental rheological law of the Lesser Himalayan quarzites could be defined. The determination of this law brings an additional constrain to the knowledge of the rheological structure of the Himalayan continental lithosphere, an essential parameter in the mechanical models of the seismic cycle.
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https://tel.archives-ouvertes.fr/tel-00130535
Contributor : Pierre Bettinelli <>
Submitted on : Monday, February 12, 2007 - 4:03:50 PM
Last modification on : Thursday, December 10, 2020 - 3:05:50 AM
Long-term archiving on: : Tuesday, April 6, 2010 - 8:53:37 PM

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  • HAL Id : tel-00130535, version 1

Citation

Pierre Bettinelli. Déformation Intersismique de l'Himalaya du Népal à partir de données GPS. Géophysique [physics.geo-ph]. Institut de physique du globe de paris - IPGP, 2007. Français. ⟨tel-00130535⟩

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