The Bay Area Regional Deformation (BARD) network of permanent, continuously operating Global Positioning System (GPS) receivers monitors crustal deformation in the San Francisco Bay area and northern California. It is a cooperative effort of the Berkeley Seismological Laboratory at UC Berkeley (BSL), the US Geological Survey (USGS), and several other academic, commercial, and governmental institutions. Started in 1991 with 2 stations spanning the Hayward fault, BARD now includes 32 permanent stations and will expand to 40 stations in 1998 (Figure 1). The principal goals of the BARD network are: 1) to determine the distribution of deformation in northern California across the wide Pacific-North America plate boundary from the Sierras to the Farallon Islands; 2) to estimate three-dimensional interseismic strain accumulation along the San Andreas fault system in the San Francisco Bay area to assess seismic hazards; 3) to monitor hazardous faults and volcanoes for emergency response management; and 4) to provide infrastructure for geodetic data management and processing in northern California in support of related efforts within the BARD Consortium and with surveying, meteorological, and other interested communities.
Figure 1: Operational (solid triangles) and planned (open triangles) BARD stations in northern California (top) and in the San Francisco Bay area (bottom). The oblique Mercator projection is about the NUVEL-1 Pacific-North America Euler pole so that expected relative plate motion is parallel to the horizontal. Circled stations (will) use continuous telemetry.
BARD presently includes 32 permanent, continuously operating stations (Table 1): 15 are maintained by the BSL (including two with equipment provided by Lawrence Livermore National Laboratory, and the Satloc Corporation), 4 by the USGS, Menlo Park, California, 2 by Trimble Navigation, and 1 by Stanford University. Other stations are maintained by institutions outside of northern California, such as the National Geodetic Survey, the Jet Propulsion Laboratory, and the Scripps Institution of Oceanography, as part of larger networks devoted to real-time navigation, orbit determination, and crustal deformation. In addition, 3 stations are operated by UC Davis in a semi-permanent mode: receivers at these sites operate continuously except for brief periods when they are used for campaign-mode surveying.
Table 1: Operational and Planned BARD Stations
In 1996, the BSL acquired 13 Ashtech Z-12 receivers with Dorne-Margolin design choke ring antennas from a combination of federal (NSF), state (CLC), and private (EPRI) funding. Nine of these receivers have been installed during the past two years to densify the continuous strain measurements in the San Francisco Bay area and to consolidate the regional geodetic network. One particular focus of the station locations is several profiles between the Farallon Islands and the Sierra Nevada in order to better characterize the larger scale deformation field in northern California (Figure 1). Two more of the BSL receivers and 2 receivers owned by UC Santa Cruz will be installed during the next year. In addition, the BSL will assume operation and maintenance of the 2 semi-permanent receivers located in the south Bay region currently operated by UC Davis, and with recent federal (USGS NEHRP) funding, has purchased 2 Ashtech receivers to be permanently installed at these sites during 1998-99.
The 2 remaining BSL receivers will be part of Self-Continuous Autonomous Mobile Positioning Stations (SCAMPS) that can be deployed for short intervals within dense local subnets around the Hayward fault and in the north Bay area. Three years funding for this project, which will combine GPS and INSAR observations to infer deformation along the Hayward fault, was award by NASA in early 1998, and preliminary reconnaissance and surveys to establish suitable GPS sites are currently underway. Testing and evaluation of possible hardware systems, including less expensive L1-only receivers, will be conducted in collaboration with UNAVCO during the next year.
In 1996, researchers from the BSL, the USGS, Stanford University, LLNL, UC Davis and UC Santa Cruz formed a consortium of institutions involved in studies of the tectonic deformation in the San Francisco Bay area and northern California. Members of the BARD consortium agreed to pool existing resources and coordinate development of new ones in order to advance an integrated strategy for improving the temporal and spatial resolution of the strain field. They agreed in principle to the continued development of the network of permanently deployed GPS receivers, to the development and maintenance of a pool of GPS receivers for campaign-mode operations that, when not used in campaigns, will be deployed in semi-permanent mode in the San Francisco Bay area, to archiving of all data at the NCEDC, and to the development of a coordinated data analysis facility that will process permanent, semi- permanent, and campaign-mode data.