Shallow lithosphere structure in the north-central region of the gulf of California, Mexico, from seismic noise and earthquake tomography

Summary The potential for geothermal resources and the tectonic activity of the north-central region of the Gulf of California, Mexico (GoC) offer a good opportunity to investigate the lithospheric structure of this region. We used one year of ambient seismic noise and 11 shallow earthquakes recorded by the Gulf of California Broadband Seismological Network (RESBAN) and stations from the Northwest Mexico Seismic Network (RESNOM) and the National Seismological Service (SSN) to estimate the three-dimensional S-wave velocity structure. We used surface wave travel times at short and long periods, and a two-stage tomography technique to retrieve an S-wave velocity model. We use coarse mesh of 16×40 cells with dimensions of 20×20 km in the horizontal direction and variable up to 60 km in depth. The absolute velocity model shows three areas in depth and significant lateral changes from the north to the center of the GoC associated with crustal and upper-mantle structure. We observed variations in crustal thickness that would indicate a variable Moho depth in the northern GoC and a likely constant depth towards the center of the Gulf. We identified low-velocity anomalies that could confirm the existence of a geothermal system in the north of the Gulf. The velocity models show relative changes associated with a heterogeneous lithosphere from the central region to the north of the GoC, which would indicate a transition from weak to stronger lithosphere. Velocity anomalies explain some of the tectonic differences between the north and the central GoC, as well as geophysical observations, including heat flow measurements and seismicity.