The Grand Tour - Pacific Margin Structural Styles - Washington to Southern California

Piper, Kenneth A.¹, Michael R. Brickey² (1) Minerals Management Service, Pacific OCS Region, Camarillo, CA (2) Minerals Management Service, Pacific OCS Region,

The Pacific offshore margin displays a wide range of structural styles as graphically represented by the marine seismic profiles acquired as a part of the oil and gas exploration boom of the 1970's and 1980's. Here we display a sampling of those lines chosen to represent the depositional and deformation history of the various coastal provinces.

In the Pacific Northwest province, the seismic data show the predominantly extensional deformation of the upper plate, apparently unaffected by the subduction of the oceanic plates. Off Washington and northern Oregon, listric normal faults evoke the extensional style of the southern Great Basin. Farther south, the structural style sometimes gives the appearance of giant landslides.

South of the Mendocino fracture zone the San Andreas transform fault system has overprinted the pre-existing oceanic ridge–subduction systems that are dominant features south to Point Conception. South of San Francisco, the absence of major strike-slip faulting allows a clearer picture of the convergent influence.

South of Point Conception, the major tectonic influence has been the rotation of the Transform Ranges block and the concurrent extension of the area in its wake. Abundant volcanic ridges and deep sedimentary basins have resulted from a complex tectonic history. In the Santa Barbara Channel, early extension was followed by compression as the Transverse Ranges block rotated into an orientation that became an impediment to the relative Pacific–North American plate motions.