Crustal Structure of the Southern Gulf of California and subducting Rivera plate

We present two new seismic velocity models that compose the most detailed picture to date of the crustal structure of the southeastern Gulf of California. Wide-angle and multi-channel seismic (MCS) data were collected in 2002 using the R/V Maurice Ewing and a 480-channel, 6 km-long streamer, ocean bottom seismometers and land seismometers each spaced 10-15 km apart along transects. Both transects discussed here cross the Jalisco continental rifted margin. Compared with its conjugate rifted margin, the Cabo section of Baja California, the Jalisco margin possesses a wider zone of transitional/extended crust. The oceanic crust across the mouth of the Gulf has a thickness of ~6 km, but the thickness of the Jalisco continental crust has yet to be determined. Wide-angle modeling of the Jalisco margin indicates the presence of the Rivera plate subducting under mainland Mexico. In addition, the trench between the down going slab and rifted margin shows up clearly on prestack depth migrated images from multi-channel seismic data. Previous workers have shown from hypocenters of microearthquakes that the southern Rivera plate dips ~10 degrees down to 20 km depth and then increases to ~50 degrees by 40 km depth; however, little is known about the depth of the plate under the Jalisco rifted margin. Understanding the limits of the lateral and vertical extent of the subducting plate will constrain plate tectonic configurations and timing of events at the mouth of the Gulf.