Event seismograms from the Parkfield High Resolution Seismic Network (HRSN) from 1987 through June 1998 are available in their raw SEGY format via NCEDC research accounts. A number of events have faulty timing due to the lack or failure of a precision timesource for the network. Due to funding limitations, there is currently no ongoing work to correct the timing problems in the older events or to create MiniSEED volumes for these events. However, a preliminary catalog for a significant number of these events has been constructed, and the catalog is available via the web at the NCEDC.
As described in Chapter 6, the original HRSN acquisition system died in late 1998, and an interim system of portable RefTek recorders were installed at some of the sites. Data from this interim system are not currently available online.
In 2000 and 2001, 3 new borehole sites were installed, and the network was upgraded to operate with Quanterra Q730 data loggers and digital telemetry. The upgraded acquisition system detected events using the HRSN stations and extracts waveforms from the HRSN PASO stations. The event waveform files were automatically transferred to the NCEDC, where they were made available to the research community via anonymous ftp until they are reviewed and permanently archived. In 2000-2003 the PASO array, a temporary IRIS PASSCAL broadband network with real-time telemetry, was installed in the Parkfield area and its recording system was housed at the HRSN recording site in Parkfield. During this time, the HRSN collected event data from both the HRSN and PASO array and provided this integrated data set to researchers in near-real-time.
The HRSN 20 Hz (BP) and state-of-health channels were archived continuously at the NCEDC. As an interim measure, the NCEDC also archived the continuous 250 Hz (DP) data channels through late 2002 in order to help researchers retrieve events that were not detected during the network upgrade.
The increased seismic activity related to the magnitude 6.5 earthquake in nearby San Simeon on December 22, 2003 drastically increased the number of triggers by the HRSN network. From December 2003 through August 2004, the HRSN had over 70,000 triggers. The 56Kb frame relay connection from Parkfield to UC Berkeley, which was installed to transmit continuous 20 Hz data, selected 250 Hz channels, and event triggered 250 Hz waveforms from the network, was saturated from the increased activity. The HRSN stopped telemetering the event-triggered waveforms, and the NCEDC started to archive continuous 20 and 250 Hz data from the entire network from tapes created at the HRSN operations center in Parkfield in order to preserve this unique dataset. The seismicity again increased after the magnitude 6.0 Parkfield earthquake on September 28, 2004. The NCEDC plans to continue archiving both the continuous 250 Hz and 20 Hz data streams for the foreseeable future.
Berkeley Seismological Laboratory
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