Crustal structure of the offshore southern Santa Maria Basin and transverse ranges, southern California, from deep seismic reflection data

Abstract

Seismic reflection data from the 1986 EDGE/Pacific Gas and Electric experiment together with refraction and gravity data are used to construct an integrated north‐south geophysical cross section along the offshore Santa Maria Basin and across the offshore extension of the Transverse Ranges. Thrust faults offsetting acoustic basement and folding Miocene sediments root in a midcrustal detachment at 12–13 km depth. The detachment coincides with an increase in reflectivity seen on the seismic reflection section and the maximum depth of earthquakes. A high‐velocity oceanic crustal layer at the base of the crust (17–22 km) and Moho (≈ 25 km) is offset by a low‐angle thrust fault with an apparent dip ≈ 10° to the north offshore Point Arguello. Gravity models indicate crustal thickening and a change in the depth to Moho from 25 to 30 km in this region. However, the contribution of elastic flexure from loading of the Transverse Ranges is considered to be minor in this part of the borderland. The cross section constrains Neogene shortening to less than 3% based on faulting and folding of the sedimentary section. Shortening of the upper crust is balanced by a combination of ductile flow and subduction of the oceanic crust beneath the midcrustal detachment.