Crustal structure from 2-D gravity and magnetic data modeling, magnetic power spectrum inversion, and seismotectonics in the Laguna Salada basin, northern Baja California, Mexico

Abstract

We have constructed a 2-D model of the crustal structure that accounts for gravity and aeromagnetic data across the Laguna Salada basin, using independent inferences from seismic refraction studies and the Airy-Heiskanen model of isostatic compensa- tion, mass density and magnetic susceptibility measurements, a mass density-log from a well, and inversion of the power spectrum from magnetic anomalies. The model suggests that the Sierra Juárez root extends down to about 42 km depth. The crust-mantle interface is at about 25 km depth in the Laguna Salada basin, the Sierra Cucapá, and the western side of the Mexicali valley. The base of magnetized crust is at about 16 km depth under the Sierra Cucapá. The geometry of the basin suggests a half-graben structure dipping eastward. The maximum sedimentary fill is about 3 km thick. The seismogenic zone is about 20 km thick, in good agreement with the depth to the base of the crustal magnetic layer. In the Laguna Salada basin, clusters of events indicate zones of weakness. Hypocenter depths were confined at a depth of up to 19.6 km, being deeper at the margins of Laguna Salada basin. The seismicity pattern correlates well with the regional fault system. Focal mechanisms suggest transtensional deformation in agreement with the regional tectonic framework.