143 The EarthScope Program: Recent Results and Future Projects

Tuesday, 11 October 2011
8:00 AM - 12:00 PM
Room 101A-C

THE SALTON SEISMIC IMAGING PROJECT (SSIP): RIFT PROCESSES IN THE SALTON TROUGH

Paper number: 143-10
Program: Technical Sessions
Time: 10:15 AM – 10:30 AM

Authors

Abstract

The Salton Seismic Imaging Project (SSIP) acquired seismic data in and across the Pacific-North America plate boundary zone, at the Salton Trough in southern California and northwestern Mexico, in March 2011. SSIP is investigating both rifting processes at the northern end of the Gulf of California extensional province and earthquake hazards at the southern end of the San Andreas Fault system. SSIP acquired seven lines of land refraction and low-fold reflection data in the Coachella, Imperial, and Mexicali Valleys, airguns and OBS data in the Salton Sea, and a line of broadband stations across the trough. The controlled-source projects utilized over 90 field personnel, a majority of whom were student volunteers. Seismometers were deployed at 4235 locations at 50-500 m spacing onshore, and at 78 locations on the floor of the Salton Sea. These stations recorded 126 onshore explosive shots of up to 1400 kg and several lines of airgun shots. A separate installation of broadband sensors at 42 sites for up to 18 months was designed to record the controlled sources as well as ambient noise and regional and global seismicity.

This poster focuses on data acquired primarily to investigate the processes of continental breakup. Previous studies suggest that, in the central Salton Trough, North American lithosphere has been rifted completely apart. To investigate crustal and uppermost mantle structure and tectonics, we acquired two 220-230 km seismic refraction / wide-angle reflection lines across and along the Salton Trough. Line 1 comprises 35 shots on land along the trough axis, parallel to the direction of Pacific-North America plate motion; this will illuminate both active rifting and adjacent extended lithosphere in the rift valley. The southeastern end of this line, in Baja California, crosses the Cerro Prieto fault. Line 2 crossed perpendicular to the trough at the location of the northern Imperial Fault in order to image structural variations across the rift, the rift flanks, and the structure of the major bounding blocks: the Peninsular Ranges and southern Chocolate Mountains. Refracted arrivals at 7.9 - 8.0 km/s, seen on sections of both of these lines, provide constraints on Moho geometry. Initial data from the onland shots are used to constrain the style of continental breakup and the partitioning of oblique extension.