HR: 15:00h
AN: T33F-06    [Abstracts]
TI: Great paleoearthquakes of the central Himalaya and their implications for seismotectonic models and seismic hazard assessment
AU: * Yule, D
EM: j.d.yule@csun.edu
AF: California State University Northridge, Department of Geological Sciences, Northridge, CA 91001, United States
AU: Lave, J
EM: jlave@crpg.cnrs-nancy.fr
AF: Nancy-Universite, Géosciences et génie civil, Nancy, F-54501, France
AU: kumar, s
EM: senthil@civil.iisc.ernet.in
AF: Indian Institute of Science, Department of Geotechnical Engineering, Bangalore, 560 012, India
AU: wesnousky, s
EM: stevew@seismo.unr.edu
AF: University of Nevada at Reno, Center for Neotectonic Studies, Reno, NV 89557, United States
AB: A growing body of paleoseismic data collected from more than ten sites in Nepal and India has documented large coseismic displacements at the thrust front (Main Frontal thrust (MFT)). Three great earthquakes have been identified: in ~A.D. 1410 centered north of Delhi, in A.D. 1505 centered in far-western Nepal, and in ~A.D. 1100 centered in eastern Nepal. It is noteworthy that wherever exposures of the MFT have been studied estimates of surface slip are consistently large; with a range of 9-26 m. Historic accounts of the 1505 earthquake describe strong shaking across a 600-km-long stretch of the central Himalaya. A magnitude for this event is estimated to be >Mw 8.5 based on the maximum extent of felt strong shaking, the 100 km width of the locked portion of the basal detachment, and an average slip of 10-15 m. Though no historic accounts exist for the ~1410 and ~1100 earthquakes, the similarity between their surface expression and the 1505 rupture suggests that these events may have been equally large. These surface-rupturing earthquakes are distinctly different from a host of blind thrust events (Mw 7.5-8.4) that dominate the historic record since A.D. 1505. Both blind and emergent earthquakes are presumed to rupture the basal detachment and release interseismic strain that accumulates near the base of the High Himalaya and carry it to the thrust front where Holocene shortening occurs at rates of 15-22 mm/yr. Whereas the surface-rupturing earthquakes clearly deform the thrust front, survey data from the region affected by the 1906 Dehra Dun earthquake suggest that blind events contribute negligible, if any, deformation to the frontal structures. The factors controlling whether or not surface rupture occurs on the MFT remain unconstrained, but the current data seem to suggest that >Mw 8.5 surface-rutpuring earthquakes are the primary contributors to the shortening observed at the thrust front. It is sobering to consider that the ‘Big One' has not struck the Himalaya in over 500 years and that Mw 7.5-8.4 earthquakes are the ‘moderate' earthquakes'. Further study to constrain the lateral extent and recurrence of the great paleoearthquakes of the central Himalaya is critical to answer important questions about the Himalaya earthquake cycle and the seismic hazard facing the rapidly urbanizing population of the region.
DE: 1217 Time variable gravity (7223, 7230)
DE: 8002 Continental neotectonics (8107)
DE: 8036 Paleoseismology (7221)
DE: 8108 Continental tectonics: compressional
DE: 8123 Dynamics: seismotectonics
SC: Tectonophysics [T]
MN: 2007 Fall Meeting