Change in NCSN Earthquake Catalog
August 1, 1995
The USGS Northern California Seismic Network (NCSN) has implemented a new policy regarding the archival of automatically timed (RTP) earthquake data in their catalog at the NCEDC. The RTP is an automated system that automatically picks seismic phases, and is used for rapid earthquake response.
Formerly, all locations that were derived from only RTP data were reviewed by analysts, but otherwise no restrictions were applied to the RTP data archived at the NCEDC.
As of August 1, 1995, RTP earthquake data will no longer be reviewed by analysts. To minimize the archival of poor quality RTP information, earthquake locations that are derived soley from RTP phase readings meet ALL of the following criteria to be included in the NCSN catalog:
- The location must be determined from at least 5 P-readings.
- The location must have an RMS < 0.5 seconds.
- The location must have an azimuthal gap < 235 degrees.
- The location must fall within the following polygon:
- 36:41.08 -117:47.58
- 37:45.00 -118:15.00
- 37:48.30 -120:09.30
- 42:18.00 -121:30.00
- 42:18.00 -125:30.00
- 40:00.00 -125:30.00
- 34:41.67 -121:22.78
- 37:45.00 -118:15.00
- 36:41.08 -117:47.58
This change may affect the completeness of the catalog at the lower magnitude levels. There has been NO change in the policy or procedures for including or reviewing events that acquired by the CUSP data acquisition system. Events aqcuired by the CUSP data acquisition system will continue to be reviewed by analysts.
Questions about the NCSN catalog located at the NCEDC can be directed to Dave Oppenheimer at the USGS, oppen@usgs.gov.
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Northern California Earthquake Data Center
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Copyright 1995-2005, The Regents of the University of California.
Last modified: Mon Dec 17 17:31:07 PST 2007