9526862 Johnson This research involves the acquisition of medium and high- resolution seismic images of the low-angle Santa Rita normal fault, near Tucson, Arizona, to resolve the question of its connection to shallower, steeper, potentially seismogenically active faults identified at the surface. Focal mechanisms for large (M=6 or larger) normal-faulting earthquakes in extensional terranes suggest that seismogenic normal faults have dips that range from 30 to 70 degrees. At the same time, geologic relationships suggest that large, low-angle normal faults (dips of less than 30 degrees) may have accommodated large-scale crustal extension. These disparate observations are often reconciled by arguments that low-angle faults slip aseismically, or, low-angle faults at depth rotate to high angle at the surface. This work will attempt to provide an example of the latter argument. This research is a component of the National Earthquake Hazard Reduction Program. ***
