BARD (Bay Area Regional Deformation network) is a network of permanent, continuously operating GPS receivers which monitors crustal deformation in the San Francisco Bay Area and northern California. Started in 1991 with two stations spanning the Hayward Fault, BARD has been a collaborative effort between the Berkeley Seismological Laboratory (BSL), the USGS at Menlo Park (USGS/MP), and several other academic, commercial and governmental institutions. At its peak, BARD collected data continuously from over 60 permanent stations in northern California, of which about half were operated by the BSL. Most of the BSL stations were collocated with broadband seismic stations of the Berkeley Digital Seismic Network (BDSN), allowing the acquisition of GPS data in real time through shared telemetry (Romanowicz et al., 1994). Data are archived at the Northern California Earthquake Data Center (NCEDC), where they are available to the public over the internet. BARD has also made its data available to the community through the UNAVCO seamless archive (formerly GSAC). With the advent of the Plate Boundary Observatory (PBO), many of the BARD stations have been folded into the PBO C-GPS network. Currently, 26 stations remain in BARD, and are operated and maintained by the BSL. These stations are located along hazardous faults in the San Francisco Bay Area, and/or are collocated with seismic broadband stations of the BDSN (3.18). One station is in the process of being installed (BDM1, Black Diamond Mine). Typically acquiring data at standard sampling intervals of 15 or 30 s, many of these stations have been upgraded to high rate sampling (1Hz) over the last few years. These are stations where the combination of receiver type and telemetry bandwidth have allowed this upgrade (Table 3.11).
Of the 26 BARD sites, eleven (Table 3.11) are co-located with broadband seismic stations of the BDSN with which they share continuous frame-relay telemetry to UC Berkeley. Where old GPS receivers are installed at these sites, the Quanterra data loggers store GPS data converted to MiniSEED format so they can be retrieved (Perin et al., 1998). This provides more robust data recovery from onsite backup on the Quanterra disks following a telemetry outage. New receivers have data storage and retrieval capabilities. One station is contributed by UC Davis (UCD1). Data from this station are collected continuously over the Internet.
Five stations (SVIN, MHDL, OHLN, OXMT and SBRN) were installed between 2002 and 2006 in the SFBA and in particular along the Hayward fault. These stations represent Berkeley's part, with significant participation of the USGS/MP, of a multi-institutional effort funded by the Major Research Infrastructure (MRI) program of the NSF to improve strain monitoring in the SFBA using an integrated approach (Murray et al., 2002a). The instrumentation at these stations includes 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 (Plate Boundary Observatory), 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. We developed a self-centering GPS antenna mount for the top of the borehole casings. These are mechanically isolated from the upper few meters of the ground. The system provides a stable, compact monument that allows access to the top of the borehole casing for downhole maintenance. GPS receivers were progressively installed at these sites and connected to Quanterra 4120 data loggers, which provide backup and telemetry capabilities. In addition, low sampling rate data (600 sec sampling) are retrieved from all the mini-PBO sites by the USGS via a GOES satellite system. Sll the sites are successfully measuring strains due to tidal effects and to local and teleseismic earthquakes (Murray et al., 2002b).
There is growing interest in collecting data at higher rates 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. We have progressively upgraded the telemetry to continuous 1 Hz telemetry: 21 stations currently provide 1Hz data, with varying degrees of robustness. 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/). At stations equipped with Ashtech A-Z12's, this upgrade is in general not feasible because of insufficient data compression.
All data collected from BARD/BSL are publicly available at the NCEDC (http://www.ncedc.org/ncedc/access.html#gps).
Ten BARD stations are currently equipped with high performance NETRS receivers, which have sufficient internal buffering to allow robust real time telemetry at 1Hz. Most recently recently we upgraded MODB to NETRS (Sept 2009). This allows us to telemeter 1Hz data from this site using the USGS VSAT system that collects seismic broadband data as part of the National Seismic Network (NSN). Other stations are still equipped with aging Z-12 receivers, which were originally programmed to record data once every 30 s. At these sites, the data are collected using direct serial connections and are susceptible to data loss during telemetry outages. Several stations are equipped with Ashtech MicroZ-CGRS (uZ). We also changed our data strategy by allowing some data to be transferred by web-based telemetry (ADSL lines). This will reduce our communication operational costs and we hope will not affect our ability to react in a large event.
We hope to upgrade the remaining old receivers over the next 2 years with ARRA funding, for which we applied to the USGS in October 2009. We also propose to install new C-GPS stations at 7 sites collocated with BDSN stations that have sufficient skyview.
The BARD stations with old GPS receivers that are collocated with broadband seismometers use the BDSN Quanterra data loggers (Table 3.11) for data acquisition. With the support of IRIS (Incorporated Research Institutions in Seismology), we developed software that converts continuous GPS data to MiniSEED opaque blockettes that are stored and retrieved from the Quanterra data loggers (Perin et al., 1998), providing more robust data recovery from onsite disks following telemetry outages.
Each BSL/BARD station uses a low-multipath choke-ring antenna. With the exception of the ``mini-PBO'' sites, these 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 rock outcrop to improve long-term monument stability. Low-loss antenna cable is used to minimize signal degradation at sites where long cable runs would normally require signal amplification. Low-voltage cutoff devices are installed to improve receiver performance following power outages. 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.
BSL is acquiring high rate GPS data from 13 stations in the Parkfield (CA) region that are operated and maintained by UC San Diego. These stations were installed as part of the collaborative NSF/MRI program between the BSL, UC San Diego and Carnegie Institution of Washington nicknamed ``mini-PBO''. Since September 2009, 1Hz GPS data from these 13 stations flow through the T1 line from Parkfield to Menlo Park and then on to Berkeley. From here it is sent back to UCSD via a NTRIP server. We plan to participate in a State wide real time geodetic network that will eventually be integrated with the CISN for earthquake notification purposes. The acquisition of real time data from the Parkfield subnetwork is the first step towards linking southern and northern California real time GPS networks.
The NCEDC, operated jointly by the BSL and USGS, archives all permanent-site GPS data currently being collected in Northern California. We also archive data from the Federal Aviation Administration (FAA) sites all along the Pacific coast (the closest one is ZOA1). Data importation and quality assurance are automated, although some manual correction of unusual data problems is still required.
As part of the activities funded by the USGS through the BARD network, the NCEDC has established an archive of the 7000+ survey-mode occupations collected by the USGS since 1992. The NCEDC continues to archive non-continuous survey GPS data. The initial dataset archived is the survey GPS data collected by the USGS Menlo Park for Northern California and other locations. The NCEDC is the principal archive for this dataset. Significant quality control efforts were implemented by the NCEDC (Romanowicz et al., 1994) to ensure that raw data, scanned site log sheets, and RINEX data are archived for each survey. All of the USGS MP GPS data has been transferred to the NCEDC and virtually all of the data from 1992 to the present has been archived and is available for distribution. Together with graduate students in the department who now use the GAMIT software to process survey-mode data in the San Francisco Bay area, we are working to combine the survey-mode and C-GPS solutions into a self-consistent velocity field for Northern California. The campaign velocity field computed from campaign measurements by UCB and USGS groups has been published by d`Alessio et al., (2005).
Data from five of our sites (HOPB, MHCB, CMBB, OHLN, and YBHB) are sent to the National Geodetic Survey (NGS) in the framework of the CORS (Continuous Operating Reference Stations) project (http://www.ngs.noaa.gov/CORS/). The data from these five sites are also distributed to the public through the CORS FTP site.
In 2008, we started a collaboration with Mr. Jim Swanson, of East Bay Regional Parks (EBRP) to establish robust high rate telemetry from 11 PBO stations located on EBRP land to UC Berkeley, as part of BARD (Figure 3.19). The EBRP interest is in establishing on the fly differential GPS measurements using a hand-held device (RTK corrections), to support surveyors in the Parks. This work has been stalled, but we have proposed to establish the necessary radio telemetry using ARRA support. Five sites have line-of-sight to one of our BARD stations (DIAB or MONB). The data can be transmitted via simplex radio connections to and from these sites, and use existing frame-relay lines. For the remaining 6 sites, we propose a solution involving radio telemetry through three repeater sites. These will be equipped with switches to combine data from 2-3 stations and relay them to Berkeley. PBO is currently streaming data from these sites using an NTRIP server, but over cell modems, in a fashion that is not reliable enough for use in earthquake notification (cell modems will likely not perform well in the case of a large damaging earthquake, in particular due to saturation of the network). We hope to finalize this project within the next year, with the help of ARRA funds.
Permit requests: The permit for PTP1 has been approved by EBRP and delayed by the Real Estate Office at Berkeley. The administrative problems have been resolved, and drilling as well as the installation of the GPS equipment is imminent.
Meteorological Sensors and troposphere: In the past year, we performed some calibration tests using different meteorological sensors and collecting data at stations SBRN and BRIB (see chapter (7). We hope to install such sensors at all BARD stations to provide tropospheric corrections and achieve higher accuracy.
We use the GAMIT/GLOBK software developed at MIT and SIO to process data from BARD and other nearby continuous GPS networks (King and Bock, 1999, Herring, 2005). Data from more than 80 stations, including global IGS stations, are included in daily solutions by GAMIT. The loosely constrained solutions are then combined using a Kalman filter approach and stabilized to a defined reference frame within GLOBK. The estimated relative baseline determinations typically have 2-4 mm long-term scatter in the horizontal components and 10-20 mm scatter in the vertical. The BARD dataset has been processed in the ITRF2000 (Altamimi et al., 2002). All the BARD sites have been processed jointly with IGS sites in California. No a priori constraints are assumed. The solutions (Houlié and Romanowicz, 2009) are in good agreement with previous campaign solutions (e.g. d'Alessio et al., 2005). BARD stations are also an important component of the Bay Area velocity unification (BAVU), undertaken by Prof. Roland Bürgmann. BAVU uses the BARD routine daily solutions and combines them with continuous and campaign GPS data from multiple agencies throughout the greater SFBA (Figure 3.20).
Since the departure of Mark Murray at the end of 2005 and Nicolas Houlié in July 2009, Barbara Romanowicz oversees the BARD program, with help from Ingrid Johanson who will take over in February 2010. Rich Clymer, Bill Karavas, Rick Lellinger, John Friday, Nicolas Houlié, and Doug Neuhauser contributed to the operation of the BARD network in 2008-09. The operation of the BARD network is partially supported by funding from the USGS/NEHRP program.
Altamimi, Z., P. Sillard, and C. Boucher , ITRF2000: A new release of the International Terrestrial Reference Frame for earth science applications, J. Geophys. Res., 107(B10), 2214, doi:10.1029/2001JB000561, 2002
Artru, J., P., Lognonné and E., Blanc, Normal modes modeling of post-seismic ionospheric oscillations, Geophys. Res. Lett., 28, 697-700, 2001
d'Alessio, M. A., I. A. Johanson, R. Bürgmann, D. A. Schmidt, and M. H. Murray, Slicing up the San Francisco Bay Area: Block kinematics from GPS-derived surface velocities, J. Geophys. Res., 110, B06403, doi:10.1029/2004JB003496, 2005.
Ducic, V., J. Artru and P. Lognonné, Ionospheric remote sensing of the Denali Earthquake Rayleigh surface waves, Geophys. Res. Lett., 30, 18, 2003
Houlié, N. and Romanowicz, B., CALREF, a stable reference frame for the Northern California, in revision, PEPI.
Larson, Using 1-Hz GPS Data to Measure Deformations Caused by the Denali Fault Earthquake, Science, 300, 1421-1424, 2003
Murray, M., Neuhauser D., Gee, L., Dreger, D., Basset, A., and Romanowicz, B., Combining real-time seismic and geodetic data to improve rapid earthquake information , EOS. Trans. AGU, 83(47), G52A-0957, 2002.
Perin, B. J., C. M. Meertens, D. S. Neuhauser, D. R. Baxter, M. H. Murray, and R. Butler, Institutional collaborations for joint seismic and GPS measurements, Seismol. Res. Lett., 69, 159, 1998.
Romanowicz, B., B. Bogaert, D. Neuhauser, and D. Oppenheimer, Accessing northern California earthquake data via Internet, EOS Trans. AGU, 75, 257-260, 1994.
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