Calpine/LBL Geysers data added to the NCEDC
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.