HR: 09:05h
AN: T31G-05    [Abstracts]
TI: Structural geometry and seismicity of the Coalinga - Kettleman Hills blind-thrust system
AU: * Guzofski, C A
EM: guzofski@fas.harvard.edu
AF: Dept. of Earth and Planetary Sciences, Harvard University 20 Oxford St., Cambridge, MA 02138 United States
AU: Shaw, J H
EM: shaw@eps.harvard.edu
AF: Dept. of Earth and Planetary Sciences, Harvard University 20 Oxford St., Cambridge, MA 02138 United States
AU: Lin, G
EM: gulin@ucsd.edu
AF: Institute of Geophysics and Planetary Physics Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0225 United States
AU: Shearer, P M
EM: pshearer@ucsd.edu
AF: Institute of Geophysics and Planetary Physics Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0225 United States
AB: The 1982 New Idria (Mw = 5.4), 1983 Coalinga (Mw = 6.5), and the 1985 Kettleman Hills (Mw = 6.1) earthquakes provide one of the clearest examples of damaging earthquakes occurring on a segmented blind-thrust system that is manifest at the surface in a series of en-echelon anticlines. These events lacked any surface rupture, but had uplift signatures associated with the anticlines, arguing for a direct relationship between blind thrust faulting, folding, and surface deformation. To investigate this relationship between coseismic folding and faulting, we present a new three-dimensional (3-D) structural model of the Coalinga - Kettleman Hills fold-and-thrust belt on the western border of the San Joaquin basin in central California. Using seismic reflection profiles, surface geology, well-bore data, and seismicity, we interpret the Coalinga anticline as being comprised of a stack of imbricated structural wedges, related to two major fault ramps at depth. These two forethrust ramps share a common upper detachment surface and merge with backthrusts to generate the gross morphology of the Coalinga anticline. The prominent forelimb of the Coalinga anticline that is expressed at the surface records slip on a fault that has branched off of this upper detachment surface. Based on our analysis, slip on the upper fault ramp causes folding of the Coalinga anticline, whereas displacement of the lower thrust ramp focuses deformation in a buried monoclinal limb that lies to the east of the mapped anticline. Based on hypocentral locations, the 1983 Coalinga (Mw = 6.5) mainshock ruptured the lowermost of these two ramps. To constrain the seismogenic portions of the structure, we use hypocenters from 1980 to 2002 that are relocated with L1-norm, waveform cross-correlation techniques. These relocated events illuminate a thrust ramp that strikes parallel to the axis of the Coalinga axis, but is significantly offset to the west from the hypocenter of the Kettleman Hills event. A segmented ramp of this nature is consistent with the model that a tear fault separates the ramps, which likely served as a rupture boundary for these events. In addition, moment density plots are employed to investigate how strain is accommodated in various structural compartments in the hanging wall and footwall of the thrust ramps.
DE: 8005 Folds and folding
DE: 8010 Fractures and faults
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting