Abstract: Three-Dimensional Geometry of the Active Southern California Fold and Thrust Belt
Jay Namson, Thom L. Davis
A Series of 11 Balanced Cross Sections across the southern Coast Ranges, and western and central Transverse Ranges illustrate the geometry of the late Cenozoic anticlinoria of the region and thrust faults that are responsible for their origin. Bounding the ranges and included in the cross sections are some of the most prolific hydrocarbon basins in the United States, which include the Los Angeles, Ventura, Santa Maria, and Cuyama basins. Most of the cross sections extend from the Pacific coast or offshore and terminate at the San Andreas fault. The cross sections were originally constructed at a scale of 1:24,000, using surface geologic maps, seismic reflection data, and subsurface data from over 170 oil and gas production or wildcat wells. Line-length restorations of the cross sections illustrated the geometry of basins and pre-late Cenozoic age structures and test the two-dimensional validity of the interpretations. The serial cross sections illustrate changes in structural style of the regional anticlinoria along strike and present a structural model that is internally consistent in three dimensions. A series of regional subsurface maps have been prepared from the cross sections that show the positions of the major thrust ramps of the region and how fault slip varies along strike. The fault slip varies regularly although transfer zones are indicated for several thrust ramps. The three-dimensional structural model can be related to the structural position of oil and gas fields of the region, and there are also numerous implications for earthquake hazards posed by the deep thrust ramps. The earthquake hazard implications include delineating the location and geometry of active thrust ramps, regional and local fault slip rate variations, and the probable location of fault segment boundaries of likely rupture areas.
AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994