Tectonics of Monterey Bay
Lead Scientist: Debra Stakes
Project Manager: Dave Caress

Monterey Bay is cross-cut by active faults with low seismicity and variable mechanisms. The Margin Seismology Program has demonstrated that small to moderate earthquakes on the Monterey Bay Fault zone (MBFZ) have nearly pure strike-slip mechanisms and near-vertical dips. The largest historical earthquakes appear to be on the Monterey Bay fault zone, including events on Monterey Peninsula. The northern San Gregorio Fault (SGF), in contrast, while more seismically active, has smaller events with oblique or thrust mechanisms. The results suggest that the primary strand of the SGF dips beneath Santa Cruz. The southern SGF zone, which defines Carmel Canyon and parallels the Big Sur coast, did not show any significant seismic events during the two years of instrument deployment. In addition, relocations of historical events do not show any seismic events for this strand of the SGF. The absence of seismicity could indicate that the regional strain is being fully accommodated by the adjacent strands of the MBFZ. Alternatively, this fault segment could be locked, and building strain until it is released by a large event. Although the results of the Margin Seismology Project are important and provocative, the paucity of seismic events suggests that additional information should be acquired about the three-dimensional structure of the fault planes and the presence or absence of movement along the different fault segments. We propose two efforts over the next two years:

1) Add new seismic data to the database when it is acquired during the continuing development of the MBARI corehole seismometer and LP-1 datalogger. This work would be in collaboration with Karen McNally, University of California-Santa Cruz.

2) Analyze the newly available marine multichannel seismic reflection data collected by the US Geological Survey between the Monterey Peninsula and the Golden Gate in 1990. This effort would be in collaboration with Steve Lewis, Chief Scientist on the cruise during which the data were collected as well as the MBARI collaborators, Paull and Greene.