Bathymetry and active geological structures in the Upper Gulf of California

Abstract

Bathymetric surveys made between 1994 and 1998 in the Upper Gulf of California revealed that the bottom relief is dominated by narrow, up to 50 km long, tidal ridges and intervening troughs. These sedimentary linear features are oriented NW-SE, and run across the shallow shelf to the edge of Wagner Basin. Shallow tidal ridges near the Colorado River mouth are proposed to be active, while segments in deeper water are considered as either moribund or in burial stage. Superposition of seismic swarm epicenters and a seismic reflection section on bathymetric features indicate that two major ridge-troughs structures may be related to tectonic activity in the region. Off the Sonora coast the alignment and gradient of the isobaths matches the extension of the Cerro Prieto Fault into the Gulf. A similar gradient can be seen over the west margin of the Wagner Basin, where in 1970 a seismic swarm took place (Thatcher and Brune, 1971) overlapping with a prominent ridge-trough structure in the middle of the Upper Gulf. It is believed that these major elongated features can be linked to active geological structures reflecting the geometry of the deep basement in the Wagner Basin.