High-resolution, deep-penetration seismic reflection data have recently been collected in the offshore Santa Maria basin, northern Santa Barbara Channel, and off Point Conception, California. These data reveal major post-late Miocene east-over-west thrust faulting in offshore central California. Recognizable on both dip and strike lines, the thrust faults are generally imbricate and curve downward to a basal sole thrust at depths of 1.5-3 km (4,900-9,800 ft).

The offshore Santa Maria basin is generally regarded as a wrench-style basin. However, the Hosgri and other northwest-trending faults within the basin appear to be predominantly thrusts rather than strike-slip faults. Also, detailed mapping within the basin indicates that the overall structural pattern does not fit accepted models of wrench tectonics; for example, folds have a preferred asymmetry and their axes closely parallel faults rather than lie en echelon to them. We conclude that the folds and faults as well as the present morphology of the offshore Santa Maria basin are largely due to post-late Miocene northeast-southwest compression. Similar conclusions can be drawn from the onshore Santa Maria basin on the basis of field relations and well data.

These data, and the conclusions drawn from them, raise questions as to the validity of the generally accepted notion that all California Neogene basins are products of wrench-style tectonics.

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