Operations and Maintenance

Routine maintenance tasks required this year to keep the HRSN in operation, include cleaning and replacement of corroded electrical connections, grounding adjustments, cleaning of solar panels, re-seating, resodering and replacement of faulty pre-amp circuit cards, the testing and replacement of failing batteries, and insulation and painting of battery and data logger housings to address problems with low power during cold weather.

Remote monitoring of the networks health using the Berkeley Seismological Laboratory's SeisNetWatch software are also performed to identify both problems that can be resolved over the Internet (e.g. rebooting of data acquisition systems due to clock lockups) and more serious problems requiring field visits.

Over the years, such efforts have paid off handsomely by providing exceptionally low noise recordings (Figure 6.2) of very low amplitude seismic signals produced by microearthquakes (even below magnitude -1.0) and nonvolcanic tremors.

Figure 6.2: Background noise PSD plot for the seven continuously telemetered BP.DP1 data streams from Parkfield. The data are 20 minute samples starting at 2003.225.0900 (2 AM PDT). The plots show the background noise PSD as a function of frequency for the highest available sampling rate (250 sps) vertical component data which are continuously telemetered to Berkeley. Note the relatively low PSD levels and the overall consistency for all the HRSN stations. The 2 Hz minimum in the PSD plots for the HRSN sensor arises due to the 2 Hz sensors used at these sites. Below 2 Hz, noise levels rise rapidly and the peak at 3 sec (.3 Hz) is characteristic of teleseismic noise observed throughout California. In the 2 to 5 Hz range, VCAB and JCNB have historically shown higher background noise which is believed to result from excitation modes in the local structure. A small 60 Hz blip can be seen in the SCYB curve due to its close proximity to a power-line.