The Berkeley Digital Seismic Network (BDSN) is a regional network of very broadband and strong motion seismic stations spanning northern California and linked to UC Berkeley through continuous telemetry (Figure 37.4 and Table 38.1). The network is designed to monitor regional seismic activity at the magnitude 3+ level as well as to provide high quality data for research projects in regional and global broadband seismology.
Since 1991 the BDSN has grown from the original 3 broadband stations installed in 1986-87 (BKS, SAO, MHC) to comprise 27 stations, including an autonomous ocean-bottom seismometer in Monterey Bay (MOBB). We take particular pride in high quality installations, which often involve lengthy searches for appropriate sites away from sources of low-frequency noise, as well as continuous improvements in installation procedures and careful monitoring of noise conditions and problems. Thus, although three new stations were completed, the focus of this year's technical efforts evolved to maintenance and repair, because of aging instruments, the desire for higher data rates, corrosion and outright equipment failure.
Further expansion of our network, one of BSL's long term goals, is contingent on the availability of funding and coordination with other institutions for the development of a denser state-of-the-art strong motion/broadband seismic network and joint earthquake notification system in this seismically hazardous region.
Equally important, data quality and the integrity of the established network must be preserved and remain assured despite expansion. The first generation of broadband seismometers installed by BSL have been operating for almost 25 years. At the same time, the first generation of broadband dataloggers are entering their 16th year of service. These will both require continued vigilance and greater time commitment to repairs in the future.
Twenty-four of the BDSN sites are equipped with 3 component broadband seismometers and strong-motion accelerometers, and a 24-bit digital data acquisition system or datalogger. Two additional sites (RFSB and SCCB) consist of a strong-motion accelerometer and a 24-bit digital datalogger. The ocean-bottom station MOBB is equipped with a 3 component broadband seismometer. Data from all BDSN stations, except MOBB, are transmitted to UC Berkeley using continuous telemetry. In order to insure against data loss during utility disruptions, each site has a 3-day supply of battery power and is accessible via a dialup phone line. The combination of high-dynamic range sensors and digital dataloggers ensures that the BDSN has the capability to record the full range of earthquake motion for source and structure studies. Table 38.2 lists the instrumentation at each site.
Most BDSN stations have Streckeisen STS-1 or STS-2 three-component broadband sensors (Wielandt and Streckeisen, 1982; Wielandt and Steim, 1986). A Guralp CMG-3T downhole broadband sensor contributed by LLNL is deployed in a post-hole installation at BRIB. A Guralp CMG1-T is deployed at MOBB. The strong-motion instruments are Kinemetrics FBA-23 or FBA-ES-T with 2 g dynamic range. The recording systems at all sites are either Q330, Q680, Q730, or Q4120 Quanterra dataloggers, with 3, 6, 8, or 9 channel systems. The Quanterra dataloggers employ FIR filters to extract data streams at a variety of sampling rates. In general, the BDSN stations record continuous data at .01, 0.1, 1.0, 20.0 or 40.0, and 80 or 100 samples per second, although some sites send triggered data at the highest sampling rate using the Murdock, Hutt, and Halbert event detection algorithm (Murdock and Hutt, 1983) (Table 38.3). In addition to the 6-channels of seismic data, signals from thermometers and barometers are recorded at nearly every site (Figure 38.1).
In parallel with the upgrade of the broadband network, a grant from the CalREN Foundation (California Research and Education Network) in 1994 enabled the BSL to convert data telemetry from analog leased lines to digital frame-relay connections. The frame-relay network uses digital phone circuits that can support 56 Kbit/s to 1.5 Mbit/s throughput. Since frame-relay is a packet-switched network, a site may use a single physical circuit to communicate with multiple remote sites through the use of ``permanent virtual circuits". Frame Relay Access Devices (FRADs), which replace modems in a frame-relay network, can simultaneously support multiple interfaces such as RS-232 async ports, synchronous V.35 ports, and ethernet connections. In practical terms, the upgrade to frame relay communication provides faster data telemetry between the remote sites and the BSL, remote console control of the dataloggers, additional services such as FTP and telnet to the dataloggers, data transmission to multiple sites, and the ability to communicate and transmit data from multiple instruments such as GPS receivers and/or multiple dataloggers at a single site. Today, 23 of the BDSN sites use frame-relay telemetry for all or part of their communications system.
As described in Chapter 44, data from the BDSN are acquired centrally at the BSL. These data are used for rapid earthquake reporting as well as for routine earthquake analysis (Chapters 39 and 45). As part of routine quality control (Chapter 44), power spectral density (PSD) analyses are performed weekly. Figure 38.2 shows a summary of the results for 2005-2006.
The occurrence of a significant teleseism also provides the opportunity to review station health and calibration. Figure 38.3 displays BDSN waveforms for a 7.6 deep focus earthquake in the Banda Sea region on January 27, 2006.
BDSN data are archived at the Northern California Earthquake Data Center. This is described in detail in Chapter 43.
In 1995, in collaboration with Dr. Frank Morrison, the BSL installed two well-characterized electric and magnetic field measuring systems at two sites along the San Andreas Fault which are part of the Berkeley Digital Seismic Network. Since then, magnetotelluric (MT) data have been continuously recorded at 40 Hz and 1 Hz and archived at the NCEDC (Table 38.4). At least one set of orthogonal electric dipoles measures the vector horizontal electric field, E, and three orthogonal magnetic sensors measure the vector magnetic field, B. These reference sites, now referred to as electromagnetic (EM) observatories, are co-located with seismographic sites so that the field data share the same time base, data acquisition, telemetry and archiving system as the seismometer outputs.
The MT observatories are located at Parkfield (PKD1, PKD) 300 km south of the San Francisco Bay Area, and Hollister (SAO), halfway between San Francisco and Parkfield (Figure 37.4). In 1995, initial sites were established at PKD1 and SAO, separated by a distance of 150 km, and equipped with three induction coils and two 100 m electric dipoles. PKD1 was established as a temporary seismic site, and when a permanent site (PKD) was found, a third MT observatory was installed in 1999 with three induction coils, two 100 m electric dipoles, and two 200 m electric dipoles. PKD and PKD1 ran in parallel for one month in 1999, and then the MT observatory at PKD1 was closed.
Data at the MT sites are fed to Quanterra dataloggers, shared with the collocated BDSN stations, synchronized in time by GPS and sent to the BSL via dedicated communication links.
The BSL concluded an agreement with IRIS during 2003-2004 to contribute 19 stations of the BDSN to USArray while the experiment is deployed in California. This included 17 existing stations: CMB, CVS, FARB, HOPS, HUMO, JCC, JRSC, KCC, MNRC, MOD, ORV, PACP, PKD, POTR, WDC, WENL, and YBH as well as the two new sites: GASB and MCCM.
The 19 BDSN sites provided USArray with a running start in northern California. In June of 2004, the BSL set up the software necessary to exchange data with USArray and made modifications to the dataloggers to change the BH sampling rate from 20 Hz to 40 Hz. In this third year of USArray, the BDSN has continued to use the 40 Hz sampling rate for the BH channels.
During the station installation phase for northern and central California, the BSL collaborated with USArray to identify and permit sites that might be suitable as BDSN stations, several at UC reserves and field stations. The stations currently operating at Sutter Buttes, Hat Creek Radio Observatory, Eagle Lake Biological Field Station, Kirkwood Ski Area, Ben Lomond Conservation Camp, and at the summer home of a BSL staff member (M. Hellweg) in the Sierra Nevada foothills were established with support from BSL staff. Data from these sites (Figure 37.4) are being sent directly to the BSL as well as to the Array Network Facility. In addition, the BSL is monitoring data from several other USArray stations to evaluate their performance as possible future BDSN stations when USArray moves on across the country. In particular, noise comparisons are being conducted in different frequency bands for all BDSN and USArray stations in northern California (see Chapter 44 for further details).
Given the remoteness of the off-campus stations, BDSN data acquisition equipment and systems are designed, configured, and installed so that they are both cost effective and reliable. As a result, the need for regular station visits has been reduced. Most station visits are necessitated by some catastrophic failure. The 2005-2006 fiscal year was no exception.
In a collaborative effort with USGS/NEIC (US-NSN program), satellite dishes (VSAT's) were installed 10 years ago at stations SAO, CMB and WDC. The satellite connections allow us to contribute data to the NSN, while at the same time providing a redundant telemetry path to BSL. A VSAT was also installed in 1999 at MOD, where this was the only available means of telemetry. In 2002, station HUMO was installed as a collaboration between BSL, NEIC and the IRIS/GSN and VSAT telemetry insalled as the only telecommunications link. A VSAT down-link is also provided at the BSL data center. Due to a change in satellite vendors, hardware at all installations was changed and the satellite dishes repointed in 03/04. This effort was coordinated to minimize the interruption to the data flow. In early 2006, a third site at the Marconi Center (MCCM) was added to the partnership with NEIC and the IRIS/GSN. The NEIC also provided VSAT equipment for MCCM and is described elsewhere in this report.
Since 1996, telemetry links for all the BSL stations have been upgraded to 56 kbaud digital circuits with the exception of KCC, which is located in a hydropower facility operated by Edison International within the Sierra Nevada range. Due to the remoteness of the site, access to the area is limited after the first snowfall. Planning for the upgrade of KCC began in early 2001, when BSL engineers began discussions with Edison engineers. The terrorist events of September 11, 2001 required Edison to re-evaluate their network and site security, relegating BSL's telemetry upgrade at the KCC site to the back burner until the summer of 2005.
BSL and Edison upgraded the data link from the site over a two day period in October of 2005. Ethernet connectivity over a continuous 56k baud circuit was achieved to the site.
Also at that time, BSL engineers reinstalled the external reference clock. At KCC, the datalogger is located nearly 400 meters inside a granite tunnel. Satellite clock reception at the datalogger is impossible. During the original installation in 1996, the clock was placed at the entrance of the tunnel and digital clock output signals relayed to the datalogger via solid state short haul modems. Periodically, clock quality would suffer under this arrangement.
This year, BSL engineers moved the external reference clock to the back of the tunnel (near the datalogger) and installed a high gain antenna outside the tunnel. The connection between the clock and the antenna is via a super low loss coaxial cable. The printed circuit board which provides internal/external clock functions within the Quanterra datalogger was also replaced due to age related failure.
The BSL broadband installation at Wente Brothers Vineyards (WENL) was initially installed in 1997 at the rear of an adit that is used for the aging and storage of wine. The winter of 2005-2006 brought record rainfall to northern California. During the rains, the output from both the STS-2 and FBA-EST strong motion instruments were observed to be peculiar. Engineers from BSL found that ground water had risen and was touching the bottom of the seismometers. The cooling effect of the water had altered their responses. In order to prevent damage to the instruments in the event that the water should continue to rise, the instruments were immediately removed and returned to Berkeley. After inspection and verification of their response, the instruments were reinstalled at WENL six weeks later when the water had subsided.
By design, stations of the BDSN are located in remote locations. This remoteness assures minimization of the cultural noise while providing a measure of security. Occasionally, the remoteness provides opportunity for mischief. In early 2006, such mischief occurred at the MNRC site. Vandals broke the lock off the line power meter box and switched the power off. The system continued to operate off of battery back up power until battery voltage fell critically low. BSL engineers restored the site operation with a station visit in which they turned the line power back on and installed a new lock. These simple tasks however, required five hours of round trip driving from Berkeley.
BSL has jointly operated and maintained seismic instruments with Stanford University at the Jasper Ridge site (JRSC) since June of 1994. During the past year, BSL engineers endeavored on several days to reduce offsets and long period noise at the site. Largely these efforts involved altering grounding schemes and changing power connections with varying success. Backup batteries at the site were also changed and the FBA-23 strong motion instrument was changed to accommodate 2G full scale. Concurrent to these efforts, BSL engineers worked several days at Stanford installing and troubleshooting to support a joint USGS, Stanford Bay Area ULF-EM monitoring project. BSL has a subcontract award grant for assistance in installation, telemetry and data archiving for this project. BSL engineers troubleshoot cabling, connection, power and polarity issues. Additionally, a method for injection EM and magnetic signals into the ground was developed in order to verify system operation.
As a result of aging, a number of BDSN dataloggers required repairs in 2005-2006. The dataloggers at BKS, BRK, and KCC experienced large drifts in their internal clocks as the crystal oscillators aged. These instruments were initially purchased during the network upgrades in the early 1990's. Replacement oscillators were available from the manufacturer. In each case, a backup datalogger was rotated in to replace the original unit, which was sent for service.
BSL has supported the Earthscope Transportable Array (TA) within northern California by helping to permit sites, visiting them to maintain equipment, and by providing telemetry.
During 2005-2006, the TA installed a temporary broadband station near Sutter Buttes. Located within the flat central valley of California, the Sutter Buttes are the remnant of an ancient volcano. They rise steeply 700 meters above the valley floor, and their highest point holds a cluster of commercial radio towers and support facilities. Due to the remoteness and topology of the area, the planned telemetry via the cell phone network was found to be unreliable, and no commercial telephone service is available.
Since 1997, BSL has operated a BARD GPS station by special arrangement with the radio site operator. For this station, BSL engineers installed a digital radio link to the BSL site at ORV approximately 30 kilometers away. There, the data are consolidated with that of the seismic and GPS installations at ORV, and fed via a single 56k telco circuit to Berkeley. To support the US Traveling Array, the radio hardware at Sutter Buttes was changed in 2005 to enable the radio there to act as both a repeater for the USArray seismic data and a radio transmitter for the BARD GPS data from Sutter Buttes. Correspondingly, the radio equipment at the ORV end was changed. At present, the single digital telco circuit between ORV and Berkeley thus carries data from the ORV seismic instruments and GPS, the GPS instruments at Sutter Buttes, and the USArray seismic installation.
BSL engineers made multiple site visits to both the Sutter Buttes radio installation and the US Array seismic site in order to achieve the desired network connectivity.
The Hasting Reservation is a research and natural history facility operated by the University of California system in Monterey County California. The BSL provided permitting and logistic support during placement of the USArray instrument as well a strong motion instrumentation for the site. BSL engineers visited the site to replace the failed accelerometer in early 2006.
Two new BDSN stations, Alder Springs (GASB) and Marconi Conference Center (MCCM) were completed and brought on line in 2005/2006. Both stations provide broadband and strong motion data with continuous data telemetry. No existing buildings or structures were available at these locations. BSL engineers constructed the necessary infrastructure.
The Alder Springs (GASB) site is located approximately 35 kilometers west of the central valley town of Willows. Local geology is mostly serpentine and Franciscan. In the past, a short period observatory has been operated at the Alder Springs site by the California Department of Water Resources. The GASB site is being developed in cooperation with the CREST (Consolidated Reporting of EarthquakeS and Tsunamis) network, and closes a gap in the BDSN network between stations MNRC and WDC.
In June 2004, construction began on a steel and concrete seismographic vault similar to those at JCC, PKD, HOPS, and MNRC. On-site excavation was contracted. Inmates from the CDF Valley View Conservation Camp provided labor for the concrete pour and back filling of the excavation. BSL engineers built the forms and framing for the concrete, as well as all electrical wiring at the site. The permit for this site was provided by the US Forest Service, Mendocino National Forest.
Although, physical work at the site temporarily stopped in September 2004, a frame-relay circuit was installed at the CDF camp in early January of 2005. Local loop connectivity to the vault was achieved via wireless Ethernet bridge (radio). Installation of the seismic instruments at GASB was completed in September 2005, and broadband data acquisition began.
In November 2004, BSL and the University of California signed a License Agreement to construct a seismic vault and install instruments at the Marconi Conference Center near Marshall, CA. Located along the Tomales Bay, the surface trace of the San Andreas Fault, the conference center is part of the California State Park system. The site for the station was selected for its proximity to existing utilities and to minimize the disturbances to the historical and visual elements of the park. This site was constructed with combined funding from BSL, USGS/NEIC and the IRIS/GSN and is part of the ANSS backbone network.
Following the success of the seismic vaults at HOPS, PKD, and MNRC, the vault at MCCM was constructed using a recycled, ocean going, steel shipping container. The design is advantageous in locations where existing facilities or mine adits do not exist. Construction began in February 2005, with excavation and concrete pours. However, the installation of the instrumentation was delayed until after December 2005, when the electrical power was connected. Telemetry from the site is achieved via a NEIC VSAT. The satellite installation was completed by joint efforts of BSL and NEIC engineers in February 2006.
The station has been recording data since early February 2006, and VSAT telemetry has been operating since late February. The MCCM site features a Q4120 datalogger, a STS-2 seismometer, and a FBA ES-T strong motion instrument with 2 G limit. BSL engineers are presently pursuing a permit to augment the site telemetry via digital radio repeater. This permit is expected sometime in the next year.
The Monterey Ocean Bottom Broadband observatory (MOBB) is a collaborative project between the Monterey Bay Aquarium Research Institute (MBARI) and the BSL. Supported by funds from the Packard Foundation to MBARI, NSF/OCE funds and UC Berkeley funds to BSL, its goal has been to install and operate a long-term seafloor broadband station as a first step towards extending the on-shore broadband seismic network in northern California, to the seaside of the North-America/Pacific plate boundary, providing better azimuthal coverage for regional earthquake and structure studies. It also serves the important goal of evaluating background noise in near-shore buried ocean floor seismic systems, such as may be installed as part of temporary deployments of ``leap-frogging" arrays (e.g. Ocean Mantle Dynamics Workshop, September 2002).
BSL staff put significant effort in the development of procedures to minimize instrumental noise caused by air circulation inside the seismometer package casing (see 2001-2002 and 2002-2003 BSL Annual Reports). These procedures were later applied to the preparation of 3 similar packages destined for installation on the Juan de Fuca plate in the framework of University of Washington's Keck project.
This project follows the 1997 MOISE experiment, in which a three component broadband system was deployed for a period of 3 months, 40 km off shore in Monterey Bay, with the help of MBARI's ``Point Lobos" ship and ROV ``Ventana" (Figure 38.4). MOISE was a cooperative program sponsored by MBARI, UC Berkeley and the INSU, Paris, France (Stakes et al., 1998; Romanowicz et al., 1999; Stutzmann et al., 2001). During the MOISE experiment, valuable experience was gained on the technological aspects of such deployments, which contributed to the success of the present MOBB installation.
The successful MOBB deployment took place April 9-11, 2002 and the station is currently recording data autonomously (e.g. Romanowicz et al., 2003). It comprises a 3 component very broadband CMG-1T seismometer system, a diffential pressure gauge (DPG, Cox et al., 1984) and a current meter. Data from the DPG are acquired with a sampling rate of 1 sps, and are crucial for the development and implementation of a posteriori noise deconvolution procedures to help counteract the large contribution of infragravity wave noise in the period range 20-200 sec. Procedures for removal of ingravity wave noise as well as signal generated noise have been developed (see chapter 13).
Seventeen ``dives" involving the MBARI ship ``Point Lobos" and ROV ``Ventana" have so far taken place to exchange dataloggers and battery packages during the time period 04/10/02 to 06/15/06. In February 2004, the N/S component seismometer failed. It was temporarily replaced, from 05/19/04 to 07/09/04 by one of the Keck seismometer packages which was conveniently available at that time. The original seismometer was sent back to Guralp Inc. for repair and successfully reinstalled on 07/09/04.
The data collection from the broadband seismic system is fairly complete. However, there have been recurring DPG sensor as well as DPG data storage problems in the first two years of the MOBB operation. Well recorded DPG data are available since 03/18/2004.
The MOBB station is located close to the projected path of the MARS cable (Figure 38.4) which is scheduled to be deployed in the Fall of 2006. The connection of MOBB to the MARS cable will allow continuous, real-time data acquisition from this site. Developing the interface for the connection to MARS is the object of a proposal to NSF submitted in the summer of 2006.
Under Barbara Romanowicz's general supervision, Peggy Hellweg and Doug Neuhauser oversee the BDSN data acquisition operations and Bill Karavas heads the engineering team. John Friday, Jarrett Gardner, Rick Lellinger and Bob Uhrhammer contribute to the operation of the BDSN. Karl Kappler has been responsible for the operation of the EM observatories. Bill Karavas, Bob Uhrhammer, and Peggy Hellweg contributed to the preparation of this chapter.
The California Governor's Office of Emergency Services provided funding toward the development of sites MCCM and GASB as part of the CISN. The Incorporated Research Institutions in Seismology provided matching funds for the installation of MCCM. The CREST project provided a datalogger for GASB. Earthscope (USArray) provided funds towards telemetry of northern California TA stations through BSL and operation of joint BDSN/USArray stations.
MOBB is a collaboration between the BSL and MBARI, involving Barbara Romanowicz, Bob Uhrhammer, Doug Neuhauser and David Dolenc from the BSL, and Debra Stakes and Paul McGill from MBARI. The MBARI team also includes Steve Etchemendy (Director of Marine Operations), Jon Erickson, John Ferreira, Tony Ramirez and Craig Dawe. The MOBB effort at the BSL is supported by UC Berkeley funds. MBARI supports the dives and data recovery. The MOBB seismometer package was funded by NSF/OCE grant #9911392.
The Earthscope Transportable Array provides support for telemetry and maintenance of the 19 BDSN stations from which the BSL supplies data to the USArray efforts.
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Crawford W. C., and S. C. Webb, Identifying and removing tilt noise from low- frequency (<0.1 Hz) seafloor vertical seismic data, Bull. Seis. Soc. Am., 90, 952-963, 2000.
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