Discrepancy in magnitude from database search

June 14th, 2004

June 14, 2004

We have discovered an inconsistency between the magnitudes reported in the new database search of the UC Berkeley earthquake catalogs (http://www.ncedc.org/db/Search/PI/dbselect.html) and the older, flat file search ( http://www.ncedc.org/ncedc/catalog-search.html). The inconsistency arose during the conversion of the catalog from an older PC-based database. The magnitudes currently reported in the database search were computed using a older set of station adjustments and thus differ from the magnitudes reported in the flat file search.

We are currently looking into the best way to resolve this inconsistency. For the present, we advise users for whom magnitude is a critical parameter to use the flat file search.

The NCEDC is a joint project of the University of California, Berkeley and the USGS. Please send us email at ncedcinfo@ncedc.org or fill out our comments form if you have questions or comments about these changes.

Calpine/LBL Geysers data added to the NCEDC

April 3rd, 2004

The NCEDC is pleased to announce the availability of seismic phase and waveform data from the Calpine/Lawrence Berkeley Labs seismic network that monitors seismicity in the vicinity of the Geysers geothermal field. The phase data begins 2003/04/04. Calpine/LBL stations can be recognized with their network code of "BG".

The BG data lowers the magnitude detection threshold for earthquakes at the Geysers and improves the location accuracy. For example, for the month of January, 2003 the NCSN located 248 earthquakes at the Geysers geothermal area. In that same period in 2008 we located 1,014 earthquakes, representing a four-fold increase. The large number of earthquakes that occur at the Geysers exceeds the reviewing capabilities of the NCSN staff. Consequently, only earthquakes above M1.0 at the Geysers are reviewed by analysts. Smaller magnitude events at the Geysers that are automatically detected by the CISN software are also in the catalog, but generally not reviewed.

The dense BG network allows detection of earthquakes at the Geysers with magnitudes lower than 1.0. The algorithm to compute coda durations was not designed for “short” codas (i.e., less than 7 sec). Therefore, earthquakes with magnitudes smaller than 1.0 typically have few, if any coda durations. Consequently, these small events have Md values of zero, which represents “no magnitude”. We anticipate developing a method to compute amplitude magnitudes for earthquakes below M3.0. We will then retroactively apply this method to all historic data. We have no estimated date for completion of this effort.

There is a temporary gap in BG phase data starting 2006/11/29 when the NCSN and UCB networks migrated to CISN processing software. On 2007/07/23 the NCSN established telemetry to the Calpine data acquisition system at the Geysers. This allowed the NCSN to integrate BG data into the CISN system in near real time. We have the BG phase and waveform data for this time gap, but we have no plans to integrate it into the catalog.

We expect event waveform data from the BG network for the period 2003/04/04 – 2006/11/29 to be online by the end of 2009. BG waveform data after 2007/07/23 is available, but as events only. The bandwidth of continuous waveform data recorded by the Calpine/LBL network exceeds the bandwidth of the communications link into the NCSN system. Therefore, continuous BG data is not available at the NCEDC.

The California Integrated Seismic Network greatly appreciates the cooperation of Calpine and Lawrence Berkeley Labs in monitoring earthquakes in California and their willingess to make this data set available to the public.

NCEDC archives continuous BDSN data for the 2002/11/03 Denali earthquake

March 25th, 2004

March 25, 2004

The NCEDC has archived 2 days of continuous high frequency data from the BDSN network for the days surrounding the magnitude 7.8 Denali earthquake of November 3, 2002.

Instead of the normally triggered data at sample rates of 80 or 100 Hz, the NCEDC has archived continuous data from the HH and HL channels beginning on Nov 2 and continuing through Nov 3. This provides approximately 22 hours of data prior to the event and approximately 26 hours after the event. Two stations of the BDSN are not available in this special event archive - SAO and CMB.

The NCEDC is a joint project of the University of California, Berkeley and the USGS. Please send us email at ncedcinfo@ncedc.org or fill out our comments form if you have questions or comments about these changes.

NCEDC archives continuous HRSN data following the 2003/12/22 San Simeon earthquake

February 27th, 2004

February 27, 2004

The NCEDC is archiving continuous high frequency data from the HRSN borehole network due to increased seismic activity following the magnitude 6.5 San Simeon Earthquake of December 22, 2003.

The NCEDC normally archives continuous 20 Hz data channnels (BPx) as well as triggered 250 Hz high-rate (DPx) data channels from the HRSN (BP network) borehole network in Parkfield. However, in response to a significant increase in earthquake detections by the HRSN network related to the San Simeon earthquake, the NCEDC is archiving continuous data from all data channels for the entire HRSN network starting on day 2003.355, the day before the earthquake, until seismic detections from the HRSN network drop to a reasonable level.

During time of normal seismic activity, continuous 20 Hz data and triggered 250 Hz data is transmitted in near-real time from the HRSN network operations center in Parkfield to the UC Berkeley Seismological Laboratory and the NCEDC. However the HRSN network has triggered ~ 50,000 times in the 68 days since between 2003.356 and 2004.059. Due to the increased seismic activity, we are writing the continuous HRSN data on tapes in Parkfield, and archiving the data from the tapes. Tape processing has introduced a delay of a month or more in the data archiving system as compared to the 1-3 day delay in archiving telemetered data.

Due to intermittent power problems with the solar powered stations and repeater site between the the HRSN stations and the central data collection site in Parkfield, there may be gaps in the continuous data from some sites.

The NCEDC is a joint project of the University of California, Berkeley and the USGS. Please send us email at ncedcinfo@ncedc.org or fill out our comments form if you have questions or comments about these changes.

NCEDC archives continuous BDSN data for the 2003/12/22 San Simeon Earthquake

January 28th, 2004


January 28, 2004

The NCEDC has archived 7 days of continuous high frequency data from
the BDSN network for the days surrounding the magnitude 6.5 San Simeon
Earthquake of December 22, 2003.

The NCEDC normally archives continuous 20 Hz and lower data channnels (BHx,
LHx, VHx, and UHx) as well as triggered high-rate (HHx and HLx) data channels
from the BDSN (BK network) broadband and strong motion instruments. However,
in response to users' interest in this earthquake and the possibility of
induced seismicity elsewhere in other areas, the NCEDC had archived continuous
data from all data channels for the entire BDSN network for the 7 days period
spanning 2003/12/21 - 2003/12/27 (2003.355 - 2003.361).

Due to an extended telemetry problem at Parkfield, some of the data
channels from the PKD station may be either missing or available in
triggered mode during this time.

The NCEDC is a joint project of the University of California, Berkeley and
the USGS. Please send us email at
ncedcinfo@ncedc.org or fill out our comments form
if you have questions or comments about these changes.


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