Project Description
The San Gregorio fault is categorized as a Class A fault, with a magnitude potential of 7.3 and a geologic slip rate of at least 5 mm/yr [Peterson et al., 1998]. Thus, the San Gregorio fault is the most hazardous fault in the Monterey Bay coastal region, next to the San Andreas. The Monterey Bay area is also a rapidly developing economic and population center. Clearly, it is very important to evaluate the fault hazards and earthquake fault mechanics of the local coastal margin as well as the crustal velocity structure and active tectonics.
The historic lack of sufficient seismic recording instruments in the vicinity of Monterey Bay and the use of velocity models from inland regions for earthquake hypocentral locations and focal mechanisms have led to uncertainties and inaccuracies for seismic events within Monterey Bay.
Abundant new three-component seismic data have been derived from the MBARI 1997 Project 8 and 1998 Project 4 “Margin Seismology System Development” to map the seismicity and active Monterey Bay faults and develop a detailed crustal velocity model. MBARI instrumentation includes ocean-bottom digital corehole [Stakes et al., 1998a; 1998b] and standard seismometers, and coastal digital RefTek instruments obtained from IRIS-Passcal by UC Santa Cruz.
An important goal of this study is to develop a refined map of the active fault zones in the Monterey Bay for future use in hazard-reduction evaluations as well as neotectonic reconstructions. This is directly applicable to the Marine Sanctuary's objectives and also has strong local community implications. For the first time, small earthquakes that are not located by the permanent Northern California Seismic Network (NCSN) are now being detected and located by the MBARI ocean-bottom seismometers. A more accurate picture of seismic activity levels and fault hazard is emerging. The subareal and submarine geologic data (e.g., Stakes and Rigsby [1998]) and high-resolution bathymetric data defining the San Gregorio fault warrant detailed association with well-located seismicity. These new data also address the earthquake potential of the Monterey Bay fault zone, which borders the Monterey Peninsula and Monterey Bay Aquarium.
The development and deployment of MBARI's corehole seismometers in 1998 yielded an abundance of new seismic data along the San Gregorio fault. The subsequent processing and analysis of the data is the next step to obtain new scientific results for an area of the deep ocean (San Gregorio/Monterey Bay fault zone) in which the fault characteristics are not well understood. This project represents the first major scientific accomplishments resulting from the multi-year development effort of the corehole seismometers.
Summary of Deployments from Margin Seismology Databases
(MBARI internal and special permission only)
Instructions for logging into database
| Deployment | Site Name | Site Abbreviation | Instrument | Dates Recording | Status |
|---|---|---|---|---|---|
| 98S01 | Duo Seismo | MDUO | LP1-A | 1/14/98 - 3/10/98 | Recovered |
| 98S02 | Clam Growth 1003 | MCGR | LCHEAPO-1 | 1/20/98 - 3/11/98 | Recovered |
| 98S03 | Northern Smooth Ridge | MNSR | LCHEAPO-2 | 1/29/98 - 4/20/98 | Recovered |
| 98S04 | Duo Seismo | MDUO | LP1-D | 3/10/98 - 5/13/98 | Recovered |
| 98S05 | Clam Growth 1003 | MCGR | LP1-C | 3/11/98 - 5/8/98 | Recovered |
| 98S06 | Northern Smooth Ridge | MNSR | LCHEAPO-1 | 4/20/98 - 7/24/98 | Recovered |
| 98S07 | Point Pinos Monument | MPPM | LP1-A | 4/21/98 - 7/7/98 | Recovered |
| 98S08 | Clam Growth 1003 | MCGR | LCHEAPO-2 | 5/8/98 - 7/28/98 | Recovered |
| 98S09 | Duo Seismo | MDUO | LP1-B | 5/13/98 - 7/8/98 | Recovered |
| 98S10 | Horseshoe Slump | MHRS | LP1-C | 5/14/98 - 7/27/98 | Recovered |
| 98S11 | West of Point Pinos | MPTP | LP1-D | 7/7/98 - 9/22/98 | Recovered |
| 98S12 | Duo Seismo | MDUO | LP1-E | 7/8/98 - 9/24/98 | Recovered |
| 98S13 | Northern Smooth Ridge | MNSR | LP1-A | 7/27/98 - | Not Recovered |
| 98S14 | Horseshoe Slump | MHRS | LP1-B | 7/27/98 - 9/25/98 | Recovered |
| 98S15 | Clam Growth 1003 | MCGR | LCHEAPO-1 | 7/28/98 - 10/22/98 | Recovered |
| 98S16 | West of Point Pinos | MPTP | LP1-C | 9/22/98 - 10/26/98 | Recovered |
| 98S17 | Duo Seismo | MDUO | LP1-F | 9/25/98 - 10/23/98 | Recovered |
| 98S18 | Horseshoe Slump | MHRS | LP1-D | 9/25/98 - 10/23/98 | Recovered |
Peterson, M., T. Toppozada, T. Cao, C. Cramer, M. Reichle, M. Maher, and L. Atchison, New geologic maps lend support to better building design in California earthquake country, California Geology, 51, 3-9, 1998.
Stakes, D. S., J. S. McClain, T. VanZandt, P. McGill, and M. Begnaud, Corehole seismometer development for low-noise seismic data in a long-term seafloor observatory, Geophys. Res. Lett., 25, 2745-2748, 1998a.
Stakes, D., B. Romanowicz, J. Montagner, P. Tarits, J. Karczewski, S. Etchemendy, D. Neuhauser, P. McGill, J. Koenig, J. Savary, M. Begnaud, and M. Pasyanos, MOISE: Monterey Bay Ocean Bottom International Seismic Experiment, Eos Trans. AGU., 79, 301, 308-309, 1998b.
Stakes, D. S. and C. A. Rigsby, Tectonic reconstruction of the Monterey Canyon, in prep., 1998.
Page developed by Michael Begnaud