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