HR: 1330h
AN: S52C-0151    [PDF]
TI: Results From the Expanded and Upgraded High Resolution Borehole Seismic Network (HRSN) at Parkfield, CA
AU: * Johnson, W C
EM: wade@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, Unversity of California 215 McCone Hall #4760, Berkeley, CA 94704-4760 United States
AU: Nadeau, R M
EM: nadeau@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, Unversity of California 215 McCone Hall #4760, Berkeley, CA 94704-4760 United States
AU: Clymer, R W
EM: rich@seismo.berkeley.edu
AF: Berkeley Seismological Laboratory, Unversity of California 215 McCone Hall #4760, Berkeley, CA 94704-4760 United States
AB: As part of the U.S. Geological Survey's Parkfield Prediction Experiment the HRSN of 10, 3-component borehole seismometers was installed in 1987 to monitor the evolution of seismicity to very low magnitudes (M$<$0) in the expected nucleation region of a repeating M6 earthquake. During the period 1987 thru mid-1998, high frequency broad-band width (0 to 125 Hz) seismograms from over 5100 earthquakes were recorded in a triggered mode at 500 sps on a 16-bit acquisition system. These events typically clipped at magnitudes greater than 1.5 due to the high gain levels required for small earthquake detection. Data tapes were mailed to Berkeley for processing, and assessment of HRSN performance was made only after the data tapes were read. The expected M6 has yet to occur, nonetheless, data from the HRSN has contributed markedly to our basic understanding of fault zones and earthquake physics by providing a picture of seismic evolution and earthquake recurrence on a compressed time scale (made possible by the numerous small events), and by bridging the gap between laboratory and large earthquake scales. In 1998 the aging HRSN acquisition system failed. With emergency funding from the USGS NEHRP program, the system was replaced with modern 24-bit acquisition and telemetry systems, providing on-scale recording of larger magnitude events and remote access of the system from UCB. This allows for more rapid data analysis and network trouble shooting. Coincident with the network's upgrade, and with NSF support, the HRSN was also expanded from 10 to 13 stations to improve its coverage of low magnitude seismicity at the SAFOD deep drilling site. Upgrade and expansion were completed in August of 2001, and fine tuning of operational parameters and efforts at reducing noise continues. Collection of many more microearthquakes is now possible with the new system. For example, in a 4x4x6 km deep region around SAFOD about 130 evs./yr are now being collected compared to 50 evs./yr from the original HRSN. We discuss the upgrade and expansion efforts and present recent monitoring results from the new HRSN configuration.
UR: http://www.seismo.berkeley.edu/seismo/bdsn/hrsn.overview.html
DE: 7215 Earthquake parameters
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7294 Instruments and techniques
SC: Seismology [S]
MN: 2003 Fall Meeting