THREE-DIMENSIONAL GEOMETRY AND INTERACTIONS OF FAULTS AND STRUCTURES ALONG THE NORTHERN MARGIN OF THE SANTA BARBARA CHANNEL, CALIFORNIA

A three-dimensional model of fault surfaces and stratigraphic horizons in the Ventura and eastern Santa Barbara basins was created. Faults were mapped by abrupt terminations of reflections, changes in reflection character and dip, and by fault plane reflections observed in 3D and 2D seismic reflection data. Mapping was also constrained by sea floor geology and well data. The resulting time maps were digitized and depth converted. Published fault maps and cross-sections were used to add additional fault surface maps. The moderately steeply dipping Pitas Point fault trends east-west from the coast near Ventura. The shallower dipping North Channel fault intersects the Pitas Point fault at a depth of about 1 km. Shallow thrusts, folds, and south dipping reverse faults occur in the hangingwall and footwall of the Pitas Point and North Channel faults. The Red Mountain fault splays into two main branches near the Carpinteria coast. The northern branch continues west of the UCSB campus where it may die into folding. The south branch dies out in a syncline south of Santa Barbara. The North Channel and Red Mountain faults probably intersect with depth. Displacement is transferred from one fault to another via NE-SW cross faults and probably by vertical axis block rotations. Major cross faults are mapped or inferred near Santa Paula, along the Ventura River, at Rincon Point, and at Fernald Point. Abrupt changes in shortening and fault-fold style along the strike of the Pitas Point and North Channel faults occur across these NE-SW faults. Our three-dimensional model allows visualization and analysis of the complex interaction between fault surfaces, folds, the structure of mapped horizons, and earthquake hypocenters. Evolution of this model with improved velocity structure will lead to better hypocenter locations and depth conversions. Incorporation of additional horizons and faults will yield a better picture of the subsurface structure and allow kinematic analysis and such things as earthquake ground motion modeling.