HR: 13:40h
AN: S13F-01 INVITED    [Abstracts]
TI: Relocating and Characterizing the 10 Feb 2006 "Green Canyon" Gulf of Mexico Earthquake Using Oil-Industry Data
AU: * Dellinger, J A
EM: dellinja@bp.com
AF: BP, 501 Westlake Park Blvd, Houston, TX 77079, United States
AU: Dewey, J W
EM: dewey@usgs.gov
AF: U.S. Geological Survey, MS 966, Denver, CO 80225, United States
AU: Blum, J
EM: johnblum@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UCSD, 9500 Gilman Drive, La Jolla, CA 92093- 0225, United States
AU: Nettles, M
EM: nettles@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
AB: On 10 Feb 2006, a magnitude 5.2 earthquake occurred in the Green Canyon deep-water block of the Gulf of Mexico offshore Louisiana. At the time, this was the largest earthquake in the Northern Gulf of Mexico since at least the early 1970's. This earthquake is of particular interest to the oil industry because of its location in an area of significant underwater infrastructure development. The earthquake is also of interest to the earthquake seismology community because of its unusual intra-plate location and anomalous signature. The earthquake's radiated high-frequency body waves were unusually weak compared to its surface waves, and attempts to fit the earthquake with a typical double-couple source mechanism have been unsuccessful. The event could not be well located using traditional seismic monitoring networks because of the lack of any nearby observations, especially to the South. Two nearby oil-exploration seismic surveys did serendipitously record the event from the South, however: the BP-BHP Atlantis Ocean-Bottom-Node survey, and the CGG Green-Canyon phase VIII multi-client streamer survey. These surveys' instruments were not designed for recording frequencies below 5Hz, so the earthquake signals were weak -- much weaker than the high-frequency signals from the surveys' own airguns (which is what the instruments were designed to record). However, by low-pass filtering the data and beam-forming the arrays (of several hundred receivers each) we were able to extract usable earthquake arrivals. These new seismic observations were then used by the USGS in a first-arrival traveltime inversion to relocate the earthquake. We also measured the phase velocity and azimuth of the earthquake arrivals across the arrays, and used those azimuths as an independent method of estimating the event's location. The event was also recorded by a SeaStar Tension-Leg Platform, which reported an apparent local subsidence of the seafloor of\ .8 inches associated with the event. We are currently attempting to identify the most geologically plausible scenarios that are consistent with all the available data, and determining how these might be tested by further field observations.
DE: 4219 Continental shelf and slope processes (3002)
DE: 4558 Sediment transport (1862)
DE: 4562 Topographic/bathymetric interactions
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7294 Seismic instruments and networks (0935, 3025)
SC: Seismology [S]
MN: 2007 Fall Meeting