Description of the network

The BSL currently maintains and operates 30 BARD stations (twenty-six bi-frequency sites and four L1 sites). The sampling rate varies from 1 to 30 seconds, and the data are transmitted continuously over a serial connection. Most stations use frame relay technology, either alone or in combination with radio telemetry.

Of the 30 sites, ten (BRIB, CMBB, FARB, HOPB, MHCB, ORVB, PKDB, SAOB, SUTB, YBHB) are co-located with broadband seismic stations of the BDSN with which they share continuous frame-relay telemetry to UC Berkeley. These sites use the Quanterra data loggers to store and retrieve the GPS data converted to MiniSEED format (it Perin et al., 1998). The MiniSEED approach provides more robust data recovery from onsite backup on the Quanterra disks following telemetry outages.

Another five stations (SVIN, MHDL, OHLN, OXMT and SBRN) have been installed in the last 3 years in the SFBA and along the Hayward fault as the Berkeley part of a multi-institutional effort funded by the NSF/MRI program to improve strain monitoring in the SFBA using an integrated approach, with significant participation of the USGS/MP (Murray et al., 2002). These stations include borehole tensor strainmeters, three-component borehole seismic velocity sensors, downhole pore pressure and tilt sensors, and GPS receivers. This project served as a prototype for the strainmeter installations planned for PBO, which faces many of the same station installation, configuration, and data retrieval issues we have addressed. Consequently, these 5 stations have received the nickname mini-PBO. From July 2001 to August 2002, five boreholes were drilled to about 200-m depth and equipped with tensor strainmeters recently developed by CIW and 3-component L22 (velocity) seismometers. For this project, we developed a self-centering GPS antenna mount for the top of the borehole casings, which are mechanically isolated from the upper few meters of the ground, to provide a stable, compact monument that allows access to the top of the borehole casing for downhole maintenance. The 5 GPS receivers were progressively installed and connected to Quanterra 4120 data loggers, which provide backup and telemetry capabilities. The completion of the last station (MHDL), located in the Marin Headlands, took longer because it required AC power, which PG$\&$E installed in December 2005. The site is operational since Sept 1, 2006. In addition, 10-minute interval data, which are retrieved from all the sites by the USGS via a backup GOES satellite system, show that all the sites are successfully measuring strains due to tidal effects and to local and teleseismic earthquakes.

Figure 3.15: Map of planned (green squares) and operational (red triangles) BARD GPS Sites.
\begin{figure*}\begin{center}
\epsfig{file=map_bard.eps, width=15cm}\end{center}\end{figure*}

The remaining BSL/BARD stations only record C-GPS data. Each BSL/BARD station uses a low-multipath choke-ring antenna, most of which (except the “mini-PBO” ones discussed above) are mounted to a reinforced concrete pillar approximately 0.5-1.0 meter above the ground level. The reinforcing steel bars of the pillar are drilled and cemented into a rock outcrop to improve long-term monument stability. A low-loss antenna cable is used to minimize signal degradation on the longer cable setups that normally would require signal amplification. Low-voltage cutoff devices are installed to improve receiver performance following power outages. Most stations are equipped with aging Z-12 receivers, which were originally programmed to record data once every 30 s and observe up to 12 satellites simultaneously at elevations down to the horizon. The antennas are equipped with SCIGN antenna adapters and hemispherical domes, designed to provide security and protection from weather and other natural phenomena, and to minimize differential radio propagation delays. The BSL acquired 7 Ashtech MicroZ-CGRS ($\mu$Z) receivers with NSF funding for the Mini-PBO project. These have been installed at the mini-PBO stations, and two have been used to replace failing Z12s at other stations (CMBB and MODB). At these sites, the data are collected using only direct serial connections and are susceptible to data loss during telemetry outages.

There is growing interest in collecting higher rates of data for a variety of applications. For example, GPS measurements can accurately track the propagation of earthquake dynamic motions both on the ground (e.g., Larson et al., 2003) and in the atmosphere (e.g., Artru et al., 2001, Ducic et al., 2003), providing complementary information to seismic observations (calibration of integrated acceleration and velocity sensor data) and estimates of earth structure (direct observation of surface wave propagation over the oceans). We started collecting 1 Hz observations at 2 stations (DIAB and MONB) in 2003. In the last year, we have progressively upgraded the telemetry to continuous 1 Hz telemetry at 3 additional stations (BRIB, HOPB and PTRB), where the bandwidth of the existing telemetry system allowed it. At stations collocated with broadband seismic sensors, the seismic data has priority for telemetry, because it is used in the Northern California real-time earthquake notification system (see http://www.cisn.org/ncmc/), making this upgrade more difficult and in general not feasible with the current Z12 receivers because of insufficient data compression. All data collected from BARD/BSL are publicly available at the Northern California Earthquake Data Center (NCEDC; http://www.ncedc.org/ncedc/access.html#gps).


Table 3.11: List of the BARD maintained by the BSL. Five models of receiver are operating now: Trimble 4000 SSE (T-SSE), Trimble 4000 SSI (T-SSI), Trimble NETRS, (T-NETRS), Ashtech Z12 and Ashtech Micro Z (A-UZ12). The replacement of the Ashtech Z12 by Trimble NETRS will make the receiver park more homogeneous. The telemetry types are listed in column 6. FR = Frame Relay, R = Radio, Mi= Microwave, WEB = DSL line. Some sites are transmiting data over several legs with different telemetry. Changes from last year's network table are highlighted in bold typography. The sites 27 to 30 are in progress. For these 4 sites, the instrumentation is available and permit request procedures have been started.
  Sites Lat. Lon. Receiver Telem. Sampling Collocated Location
    (deg.) (deg)   . rate Network  
1 BRIB 37.91 237.84 NETRS T1 1Hz BDSN Briones Reservation, Orinda
2 CMBB 38.03 239.61 A-UZ12 FR 1Hz BDSN Columbia College, Columbia
3 DIAB 37.87 238.08 A-Z12 FR 1Hz   Mt. Diablo
4 FARB 37.69 236.99 A-Z12 R-FR/R 15 s BDSN Farallon Island
5 EBMD 37.81 237.71 T-SSI R 1Hz   East Bay Mud Headquarter
6 HOPB 38.99 236.92 TR 4000 FR 1Hz BDSN Hopland Field Stat., Hopland
7 LUTZ 37.28 238.13 A-Z12 FR 30 s   SCC Comm., Santa Clara
8 MHCB 37.34 238.35 A-Z12 FR 1Hz BDSN Lick Obs., Mt. Hamilton
9 MHDL 37.84 237.50 T-NETRS FR 1Hz mini-PBO Marin Headland
10 MODB 41.90 239.69 A-UZ12 NSN 15 s   Modoc Plateau
11 MONB 37.48 238.13 A-Z12 FR 1Hz   Monument Peak, Milpitas
12 MUSB 37.16 240.69 A-Z12 R-Mi-FR 30 s   Musick Mt.
13 OHLN 38.00 237.72 A-UZ12 FR 1Hz mini-PBO Ohlone Park, Hercules
14 ORVB 39.55 238.49 A-Z12 FR 15 s BDSN Oroville
15 OXMT 37.49 237.57 A-UZ12 FR 1Hz mini-PBO Ox Mountain
16 PKDB 35.94 239.45 A-Z12 FR 30 s BDSN Bear Valley Ranch, Parkfield
17 PTRB 37.99 236.98 A-Z12 R-FR 1Hz   Point Reyes Lighthouse
18 SAOB 36.76 238.55 A-Z12 FR 30 s BDSN San Andreas Obs., Hollister
19 SBRN 37.68 237.58 A-Z12 FR 1Hz mini-PBO San Bruno
20 SODB 37.16 238.07 A-Z12 R-FR 30 s   Soda Springs, Los Gatos
21 SRB1 37.87 237.73 T-SSE FR 1Hz   SRB building, Berkeley
22 SUTB 39.20 238.17 A-Z12 R-FR 30 s BDSN Sutter Buttes
23 SVIN 38.03 237.47 A-UZ12 R-FR 1Hz mini-PBO St Vincents
24 TIBB 37.89 237.55 A-UZ12 R 1Hz   Tiburon
25 UCD1 38.53 238.24 NETRS WEB 1Hz   UC - Davis
26 YBHB 41.73 237.28 A-Z12 FR 15 s BDSN Yreka Blue Horn Mine, Yreka
27 BDM 37.95 238.13 NETRS     BDSN Black Diamond Mines Park, Antioch
28 MCCM 38.14 237.12 NETRS     BDSN Marconi Conference Center, Marshall
29 PTP1 38.00 237.64 NETRS     NHFN Point Pinole Regional Park
30 UCSF 37.75 237.55 NETRS       UC-San Francisco, San Francisco


Between 1993 and 2001, the BSL acquired 29 Ashtech Z-12 and Micro-Z receivers from a variety of funding sources, including from federal (NSF and USGS), state (CLC), and private (EPRI) agencies. The network enhances continuous strain measurements in the Bay Area and includes several profiles between the Farallon Islands and the Sierra Nevada in order to better characterize the larger scale deformation field in northern California (Figure 3.15). During the last two years, 10 NETRS have been purchased via the UNAVCO purchase program. These receivers will help to upgrade the network to full high-rate capabilities. Three receivers are operating today (BRIB, MHDL and DIAB).

The number of continuous GPS stations in northern California is significantly increasing, with over 250 new site installations planned by 2008 as part of the Plate Boundary Observatory (PBO) component of the NSF-funded Earthscope project. UNAVCO and researchers from BARD and the other regional networks, such as SCIGN, BARGEN, and PANGA, are funded by NSF to fold operation and maintenance of about 200 existing stations, which constitute the PBO Nucleus network, into the PBO array by 2008. Two BSL-maintained stations (SUTB and MUSB) are included in the PBO Nucleus network. The other BSL stations are either collocated with seismic instrumentation or are located near the San Andreas Fault where real-time processing of the GPS data for earthquake notification is a high priority. Another 23 northern California stations, including most of the Parkfield network, will be included in the PBO Nucleus, and we are working with UNAVCO to facilitate their transition to UNAVCO control.

Berkeley Seismological Laboratory
215 McCone Hall, UC Berkeley, Berkeley, CA 94720-4760
Questions or comments? Send e-mail: www@seismo.berkeley.edu
© 2007, The Regents of the University of California