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1999 Projects: Benthic processesMargin seismology: Data processing and analysisProject lead/manager: Debra
Stakes The recent listing by the California Division of Mines and Geology of the San Gregorio Fault as a Class A fault, with an earthquake-magnitude potential of 7.3, suggests it is the most hazardous fault in the Monterey Bay coastal region, second only to the San Andreas. Historically there has been a lack of sufficient seismic recording instruments in the vicinity of the bay. Furthermore, locations and focal mechanisms for earthquakes occurring on the offshore San Gregorio Fault and recorded by land-based instruments have been derived from one-dimensional (depth) velocity models based in inland earthquakes. These limitations have led to uncertainties and inaccuracies for seismic events within Monterey Bay, especially for earthquakes at very shallow depths. During 1997 and 1998, using advanced techniques for seismic monitoring in the Monterey Bay region the MBARI margin seismology project acquired unique, high-fidelity, three-component seismic data. Instrumentation used to obtain this data included standard digital seafloor seismometers, other seismometers configured for ROV-deployment in coreholes, and coastal digital instruments. MBARI’s investment in new seismic instrumentation has proven its value in terms of better signal-to-noise ratio in the recording of seafloor seismicity. For the first time, small earthquakes and events possibly related to landslides not located by the permanent USGS seismic network have been detected and located by MBARI ocean-bottom seismometers. During 1999 seismic analysis will be completed on the data thus far collected. Findings based on this new data identify a distinctly lower-velocity path along the San Gregorio Fault down to a depth of eight kilometers. The data collected is being used to map seismicity and develop a detailed crustal velocity model. Researchers will also integrate the seismic data with new mapping data for a better understanding of the geological and tectonic evolution of Monterey Canyon. Identification of active fault zones in the bay will serve to assist in hazard-reduction evaluation. MBARI technology efforts will also focus on achieving increased endurance for batteries and data-loggers that can be used in yearlong seismometer deployments on the Juan de Fuca Ridge off the coast of Oregon. Last updated: 23 November 2005 |
