HR: 1330h
AN: T52A-0230    [PDF]
TI: Assessing lateral variations of stress and strain build up along the Himalaya from geodetic and seismicity monitoring
AU: * Bollinger, L
EM: bollinge@gps.caltech.edu
AF: Caltech, 100-23, Pasadena, CA 91125 United States
AU: Avouac, J
EM: avouac@gps.caltech.edu
AF: Caltech, 100-23, Pasadena, CA 91125 United States
AU: Cattin, R
AF: Ecole Normale Superieure, 25 rue Lhomond, Paris, 75252 France
AU: Pandey, M
AF: NSC, DMG, Katmandu, 0000 Nepal
AB: The uneven micoseismic activity along the Himalayan arc might be taken suggests significant lateral variations of stress and stress build up. On the other hand, the geodetic data show a rather uniform pattern of interseismic straining, colinear with long term geological deformation and the stress distribution as indicated from focal mechanisms. The uneven distribution of microseismicity is shown to result in fact from the influence of the topography on the stress field. The geodetic data and seismicity distribution are indeed reconciled from a model in which microseismicity is intrepreted as triggered by Coulomb stress increase due to elastic build up in the interseismic period. The model assumes a fully locked fault zone with its downdip extremity following the arcuate shape of the High Himalaya front. The observed influence of the topography requires the deviatoric stresses to be low, less than about 30 MPa, implying an apparent friction of the Main Himalayan thrust Fault of the order of 0.1. Arc normal thrusting along the Himalayan front and E-W extension in Southern Tibet are quantitatively reconciled from the model. So we can exclude that asperities on the himalayan megathrust would result from heterogeneous strain buildup in the interseismic period. Recurring transient slip events, including large earthquakes an aseismic slip event, in particular afterslip, must sum up so that heterogeneities are smoothed out in the long term. The pattern of co-seismic slip during a particular earthquake is thus probably strongly controlled by the heterogeneous stress distribution left by previous transient events.
DE: 7209 Earthquake dynamics and mechanics
DE: 8102 Continental contractional orogenic belts
SC: Tectonophysics [T]
MN: 2003 Fall Meeting