Interim 1951-1998 SFBR Seismicity Catalog
The attached seismicity list is an interim list of San Francisco Bay Region (SFBR) of local magnitude (ML) 3 and larger earthquakes which occurred between 1951 and 1998. This list is intended for use by participants in the WGCEP 99 effort and it is subject to revision.
A few CAVEATS about this interim SFBR HERP catalog:
- The catalog is a composite which is evolving as more data becomes available and more processing is completed. The catalog currently contains 1859 earthquakes with a threshold ML of 3.0. The region covered by the SFBR HERP catalog is the polygon bounded by: (39.02,-122.08),(37.19,-120.61),(36.43,-122.09),(38.23,-123.61).
- We have transcribed and processed all events with ML >= 2.9 within an area including above polygon plus a 30 km buffer zone. We have completed the transcription of the reading sheets from 1944 through 1983. The 1944 through 1950 data does not include amplitude information which is used in the calculation of magnitude.
- The 1951 starting date is dictated by the fact that amplitudes were not recorded on the Berkeley reading sheets prior to 1951 and consequently the reported magnitudes can not be checked without pulling and reading the original seismograms kept on store at Berkeley (a labor intensive project).
- Location and magnitude for the 1951 through 1968 SFBR earthquakes have been determined using data transcribed from the Berkeley reading sheets. The locations were determined using the st_relp location algorithm and a gradient layer over a half-space velocity model appropriate for the SFBR. This model and the hypocenter locations will be refined in the future as funding becomes available.
- Local magnitude (ML) for the 1969 through 1998 SFBR earthquakes have been determined from the Wood-Anderson amplitude data transcribed from the reading sheets. The primary revision in the interim SFBR HERP catalog for this interval is that the ML have formally calculated uncertainties.
- We have discovered that the ML assigned for the larger events (ML greater than ~5) recorded prior to circa 1960 is based on Pasadena records. We have evidence that these ML estimates are biased high, most likely by about 0.2 ML units. This has potentially the most significant influence on the statistical inferences drawn from the interim SFBR HERP catalog and it needs to be investigated. We have acquired the Caltech Wood-Anderson amplitude data so this analysis can proceed as time is available.
- The NCSN derived locations were adopted for the interim 1969 through 1998 SFBR HERP catalog.
- A few events do not have any uncertainties listed. This is primarily due to lack of information, and is usually due to either to inadequate information on the original reading sheets generally owing either to an insufficient number of observations or to being in the coda of a previous event.
- About 120 events (about 6.4 percent of the total) have horizontal or depth uncertainties of 10 km or larger and/or magnitude uncertainties of 0.2 ML.
Reducing the uncertainty for most of these events will likely require pulling and reading the original seismograms.
This is a manpower intensive effort that will not proceed until funding becomes available.
- Send any comments and/or suggestions to bob@seismo.berkeley.edu.
This web page is under construction. It was last updated on 28 April 1999.