Gravity and structure of the Pacific continental margin of Central Mexico

Graduation date: 1981Data collected by personnel of the Geophysics Group at Oregon State\ud University and the Instituto Oceanografico of the Direccion General dé\ud Oceanografia are used to construct a free-air anomaly map for the central\ud part of the Pacific continental margin of Mexico, which shows the gravity\ud expression of major structural features in the region. Specific features\ud are the Middle America and Rivera trenches intersected by a possible extension\ud of the Rivera Fracture Zone, and the Ulloa Trough on the western\ud side of Baja California. Of particular importance are gravimetric minimums\ud with no bathymetric expression observed east of the Tres Marias\ud Islands, southeast and northwest of the Tamayo Fracture Zone, and as extensions\ud of the bathymetrically mapped series of en echelon faults within\ud the Gulf of California.\ud A geophysical model cross section constructed along a profile southeast\ud of the Tres Marias Islands indicates a continental type crust east\ud of the islands with a Moho depth of 13 km at the base of the Tres Marias\ud Scarp and dipping toward the continent. The structure at the transition\ud zone between oceanic and continental crust suggests active subduction of\ud the oceanic crust in the past followed by a period of shear or strike-slip\ud motion. The thickness of the sediments along the cross section and\ud east of the Tres Marias Islands reaches 1.5 km