Intellectual Impact. It is proposed to construct a three-dimensional, high resolution model of the shear-velocity structure of the crust and upper mantle beneath the Gulf of California Extensional Province (GEP) and neighboring Baja California. Primary goals are to image remnants of the subducted Farallon plate, search for evidence of lithospheric delamination beneath the Peninsular Range batholith, estimate thickness of the lithosphere, map regions of melt production in the upper mantle, and extend models of crustal thickness variations to areas that are not imaged by seismic refraction or receiver function studies. Overall, these observations will help in understanding the processes involved in magma generation and rifting Baja California from the rest of the continent. The strategy for developing the model is a step-wise, iterative process involving: (1) development of a moderate-resolution 3-D model of the region using teleseismic surface waves propagating through the array of stations surrounding the Gulf, employing new array processing techniques and finite frequency response kernels; (2) integration of information on crustal structure inferred from seismic refraction experiments, gravity, noise correlation measurements of surface wave dispersion, and receiver function analysis, with interpolations based on tectonic province, geological maps and topography; and (3) use of seismograms from regional earthquakes to refine this model by comparing observed and synthetic waveforms generated in a fully 3-D model that employs equations of motion to calculate the complete elastic response. The model will be refined iteratively until the seismograms are well matched. The proposed study addresses three of the overarching themes of the Rupturing Continental Lithosphere initiative of MARGINS by (1) mapping variations in crustal thickness due to lithospheric stretching and spreading; (2) mapping apparent thickness of the mantle component of the lithosphere, including subducted fragments of the oceanic lithosphere that were intimately involved in the rupture initiation process; and (3) imaging regions of anomalously low shear velocity in the mantle that correspond to probable regions of magma generation.
Broader Impacts. As part of the MARGINS science program, this study will contribute to the understanding of the mechanisms involved in continental rifting and associated volcanism. The project will promote collaboration with geoscientists working on Baja California and the Gulf Extensional Province. The PIs will work with the MARGINS office to help disseminate their results to the wider public. Movies of wave propagation and maps of peak ground velocity and acceleration within the study area will be made available for download along with supplementary course material, examples, documentation, and meta-data. The maps can be useful in earthquake hazard assessment. This project will support the education of a graduate student and at least one undergraduate as a part-time or summer research assistant.
