The Salton Seismic Imaging Project (SSIP) acquired controlled-source seismic refraction and wide-angle reflection data in the Salton Trough, Southern California and northern Mexico, in 2011, which provide constraints on the crustal and upper mantle structure. Almost 2800 land seismometers and 50 OBS’s were deployed at almost 4300 sites, in spacing as dense as 100 m, which received seismic signals from 126 explosive shots up to 1400 kg and over 2300 airgun shots. The actively extending crust in the central Salton Trough is only 17-18 km thick, with a strongly layered but relatively one-dimensional structure for ~100 km in the direction of plate motion. This thin transitional crust is mostly new, created by metamorphism of young sediment from the Colorado River and underplating magmatism from hot upper mantle. Both seismicity distribution and thermal modeling suggest narrow brittle deformation in the upper crust and distributed ductile deformation in the lower crust. The creation of new crust keeps the crust thick and predominantly ductile, which delays the continental breakup and the initiation of seafloor spreading. If the Salton rift succeeds, this new transitional crust will become part of the continental margin.
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