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Detailed Surveys of a Transform Margin Morphology: Gulf of California, Mexico

Anderson, K.; Lundsten, E.; Paull, C.K.; Edwards, B.D.; Caress, D.W.; Thomas, H.; Gwiazda, R.; Herguera, J.C.; McGann, M.; Hinojosa, A.; Mercado, B.E.M.; Garcia, A.C.S.; Conlin, D.; and Thompson, D.R.
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In a program designed to better understand how the North American – Pacific plate boundary is manifested in the Gulf of California, a two-ship expedition was conducted in March and April 2012. Monterey Bay Aquarium Research Institute (MBARI), U.S. Geological Survey (USGS), and Center for Scientific Research and Higher Education at Ensenada, Baja California (CICESE) scientists with support of the Mexican Geological Survey led the survey of nine representative sections of the plate boundary. An autonomous underwater vehicle (AUV) collected detailed high-resolution bathymetry of the seafloor followed by remotely operated vehicle (ROV) operations that made visual ground-truth observations and recovered closely-spaced seafloor samples from the newly surveyed areas. The AUV surveys, conducted in water depths ranging between 350 to 2800 m at sites separated by three seafloor spreading centers, provided (a) high-resolution multibeam bathymetric data (vertical precision of 0.15 m; horizontal resolution of 1.0 m) as well as (b) 2-10 kHz CHIRP seismic-reflection profiles. The resulting bathymetric maps, each covering ~14 km² of seafloor, revealed the morphology of the plate boundary in unprecedented detail such that they could be used as accurate base maps for the subsequent ROV dives. For example, the bathymetry from a survey on the southern side of the Guaymas Basin documents a narrow (few meters wide) NW-SE lineation, inferred to be the trace of an active fault that was characterized by distinct scarps and/or troughs. CHIRP profiles show offsets in reflecting horizons that extend to the modern seafloor, further supporting the concept that these lineations are the trace of the active fault.


AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013