Station Maintenance

Ongoing network maintenance involves regular inspection of the collected seismic waveform data and spectra for nearby seismic events, and also from noise samples. Other common problems include changes to background noise levels due to ground loops and failing preamps, as well as power and telemetry issues. Troubleshooting and remediation of problems often require a coordinated effort, with a technician at the BSL to examine seismic waveforms and spectra while the field technicians are still on site. BSL technicians and researchers regularly review data and assist in troubleshooting.

The NHFN station hardware has proven to be relatively reliable. Nonetheless, numerous maintenance and performance enhancement measures are still carried out. In particular, when a new station is added to the backbone, extensive testing and correction for sources of instrumental noise (e.g., grounding related issues) and telemetry through-put are carried out to optimize the sensitivity of the station. Examples of maintenance and enhancement measures that are typically performed include: 1) tests on radio links to ascertain reasons for unusually large numbers of dropped packets, 2) trouble shooting sporadic problems with numerous frame relay telemetry dropouts, 3) manual power recycle and testing of hung Quanterra data loggers, 4) replacement of blown fuses or other problems relating to dead channels identified through remote monitoring at the BSL, 5) repair of frame relay and power supply problems when they arise, and 6) correctingtenna problems that arise due to various causes,such as weather or cultural activity.

Quality Control

Figure 3.11: Plot of unfiltered P-wave seismograms, recorded on the geophones of the 14 operational NHFN borehole stations for a recent Bay Area earthquake (20 July 2007, M4.2 Piedmont, CA). The stations have been ordered by increasing distance from the event (top to bottom). It is immediately apparent from this simple display that station MHDL was dead and needed immediate attention.
\epsfig{file=nhfn07_lcl.eps, width=8cm}\end{center}\end{figure}

Table 3.7: Typical data streams acquired at NHFN sites, with channel name, sampling rate, sampling mode and FIR filter type. C indicates continuous, T triggered, Ca causal, and Ac acausal. Typically the DP1 continuous channel is archived and the remaining high sample rate data (i.e., CL and DP channels) are archived as triggered snippets. Prior to Sept. 2004, however, only triggered data was archived for all high sample rate channels.
Sensor Channel Rate (sps) Mode FIR
Accelerometer CL? 500.0 T Ca
Accelerometer HL? 200.0 C Ca
Accelerometer BL? 20.0 C Ac
Accelerometer LL? 1.0 C Ac
Geophone DP? 500.0 T,C Ca
Geophone EP? 200.0 C Ca
Geophone EP? 100.0 C Ca
Geophone BP? 20.0 C Ac
Geophone LP? 1.0 C Ac

Berkeley Seismological Laboratory
215 McCone Hall, UC Berkeley, Berkeley, CA 94720-4760
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