Enhancing HRSN Performance

Detection, monitoring, and high-resolution recording of low-amplitude nonvolcanic tremors and earthquakes down to the smallest possible magnitude with the highest possible signal-to-noise (especially in the region of SAFOD drilling) are major objectives of the HRSN data collection effort. The minimization of data loss due to station outages and data-dropouts is critical to these objectives.

Over the past several years we have had a serious decline in the robustness of the power system components (primarily the aging solar panels and batteries that have been in use since initiation of the network in 1987) of the network. Simultaneous outages at multiple stations are now becoming an all too frequent occurrence and are seriously affecting efforts to monitor tremor and micro- and repeating earthquake activity in the Parkfield area.

For example, during the winter of late 2004/early 2005, monitoring for nonvolcanic tremor activity using a standard detection set of 8 HRSN channels revealed significant (and sometimes catastrophic) gaps in the data. Figure 6.3 illustrates the seriousness of the problem with an example from tremor monitoring during periods of overcast weather. During the 7 day period shown, all 8 stations used for monitoring tremor activity were out simultaneously for over 50% of the time. The remaining 50% of the time, outages occurred for at least some of these 8 stations, resulting in significantly degraded capability for unambiguous detection of the low-amplitude tremor activity.

Figure 6.3: Stacked root-mean-square seismograms for the 8 stations of the HRSN used in monitoring tremor activity. Shown are 7 days of data starting at Hour 00 (UTC) of day 7 of 2005. Times when relative RMS amplitudes (REL-AMP) are 1.0 indicate periods when all 8 stations were out simultaneously.
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As suspected, further investigation, both remotely and on site, showed that these gaps occurred due to insufficient battery re-charge at many of the network's stations, which are remote solar powered installations. In previous years, similar but less severe data gaps have occurred during the winter months and have been attributed to overcast skies during the rainy season. Last winters exceptionally heavy rainy season exacerbated the outage problem to an intolerable level, and to avoid a potential repeat of the situation, efforts are now underway to refurbish and upgrade the solar power systems.

More specifically, the following steps are being taken: 1) replacement of the oldest batteries and switching of the remaining old batteries to the less power consuming pre-amplifiers; 2) improvement of the wiring scheme along the lines suggested by the solar power representative; 3) upgrade/replacement of solar panels. (Solar panels degrade at $\sim $ 1% per year, and newer versions have improved output. Since the installation of the HRSN over 18 years ago, the same size/format panel has gone from 40 watts to 55). This is a relatively easy field task, and should gain us 20-30% capacity at each site.

Among the three newer sites (CCRB, SCYB, LCCB), both the batteries and solar panels are relatively new. Nonetheless, stations CCRB and LCCB both had some outages last winter, which is most likely explained by the limited sunlight in these areas due to hilly terrain. We plan, therefore, to add one more solar panel at each of these sites to enhance their power system robustness.

Berkeley Seismological Laboratory
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