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 3.2 and Table 3.1). The network is designed to monitor regional seismic activity at the magnitude 3+ level as well as to provide high quality data for research 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 32 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. Maintenance and repair were an important focus of this year's efforts. Engineering and research efforts were also devoted to several projects to develop and test new instrumentation (see Chapter 3, Section 7). The project involving new electronics for the STS-1 seismometers, the E300, was completed. One is currently at KCC. We also made progress in testing a new, low-cost sensor for pressure and temperature to be installed at seismic and GPS sites. Finally, the BSL is part of a team to develop and test a new version of the STS-1 seismometer.
The expansion of our network to increase the density of state-of-the-art strong motion/broadband seismic stations and improve the joint earthquake notification system in this seismically hazardous region, one of BSL's long term goals, must be coordinated with other institutions and is contingent on the availability of funding.
Equally important to network growth, data quality and the integrity of the established network must be preserved. The first generation of broadband seismometers installed by the BSL have been operating for almost 25 years. At the same time, the first generation of broadband data loggers are entering their 17th year of service. This requires continued vigilance and the commitment of time and resources to repairs and upgrades.
Twenty-eight of the BDSN sites are equipped with three component broadband seismometers and strong-motion accelerometers, and a 24-bit digital data acquisition system or data logger. Two additional sites (RFSB and SCCB) consist of a strong-motion accelerometer and a 24-bit digital data logger. The ocean-bottom station MOBB is equipped with a three component broadband seismometer. Data from all BDSN stations are transmitted to UC Berkeley using continuous telemetry. Continuous telemetry from MOBB was implemented during the past year. In order to avoid data loss during utility disruptions, each site has a three-day supply of battery power; many are accessible via a dialup phone line. The combination of high-dynamic range sensors and digital data loggers ensures that the BDSN has the capability to record the full range of earthquake motion required for source and structure studies. Table 3.2 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 broadband sensor contributed by LLNL is deployed in a post-hole installation at BRIB. A Guralp CMG-1T is deployed at MOBB. The strong-motion instruments are Kinemetrics FBA-23, FBA-ES-T or Metrozet accelerometers with 2 g dynamic range. The recording systems at all sites are either Q330, Q680, Q730, or Q4120 Quanterra data loggers, with 3, 6, 8, or 9 channel systems. The Quanterra data loggers 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. However, at some sites, data at the highest sampling rate are sent in triggered mode using the Murdock, Hutt, and Halbert event detection algorithm (Murdock and Hutt, 1983) (Table 3.3). In addition to the 6 channels of seismic data, signals from thermometers and barometers are recorded at many locations (Figure 3.3).
As the broadband network was upgraded during the 1990s, 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. The frame-relay network uses digital phone circuits which 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 a variety of interfaces such as RS-232 async ports, synchronous V.35 ports, and ethernet connections. In practical terms, frame relay communication provides faster data telemetry between the remote sites and the BSL, remote console control of the data loggers, services such as FTP and telnet to the data loggers, data transmission to multiple sites, and the capability of transmitting data from several instruments at a single site, such as GPS receivers and/or multiple data loggers. Today, 25 of the BDSN sites use frame-relay telemetry for all or part of their communications system.
As described in Section 7, 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 (Section 2 and 8). As part of routine quality control (Section 7), power spectral density (PSD) analyses are performed continuously and are available on the internet (http://www.ncedc.org/ncedc/PDF/html/). The occurrence of a significant teleseism also provides the opportunity to review station health and calibration. Figure 3.4 displays BDSN waveforms for a 7.6 earthquake in the Tonga region on March 19, 2009.
BDSN data are archived at the Northern California Earthquake Data Center. This is described in detail in Section 6
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 3.4). 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 collocated with seismometer 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 3.2). 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. Starting in 2004, new electromagnetic instrumentation was installed at various Bay Area sites in cooperation with Simon Klemperer at Stanford University. Sensors are installed at JRSC (2004), MHDL (2006) and BRIB (2006/2007).
Data at the MT sites are fed to Quanterra data loggers, shared with the collocated BDSN stations, synchronized in time by GPS and sent to the BSL via dedicated communication links.
In 2009, the BSL led a joint effort toward improving operation and maintenance of these sites with Jonathan Glen and Darcy McPhee from the USGS, and Simon Klemper at Stanford University.
Engineers from the BSL met scientists from the USGS and Stanford at the station SAO in October of 2008 to assess the condition of the EM/MT system. At that time, the EM coils were found to be not working. They were removed and returned to the manufacturer (EMI Schlumberger). In June 2009, the EM coils had not be reinstalled at SAO. EM/MT equipment at PKD was evaluated in August of 2008. There, the data logger was removed from the PKD EM/MT system and has not yet been returned.
Since it began in 1995, the EM/MT effort has suffered from minimal funding, in part due to the misconception that the EM/MT data could be recorded on unused channels in the seismic data logger. These data loggers had no channels available, however. Thus for each site, an additional data logger was purchased. In 2008, the BSL began in-house development of a low cost digitizing solution. While not as feature rich as commercially available data loggers, the prototype 24 bit digitizer was developed and is ready to be deployed for the EM/MT array. Its deployment awaits scheduling by the BSL, USGS, and Stanford University.
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. Nonetheless, many of the broadband seismometers installed by BSL are from the first generation and are now approaching 25 years in age. Concurrently, the first generation of broadband data loggers are now 17 years old. Computer systems are retired long before this age, yet the electronics that form these data acquisition systems are expected to perform without interruption.
In 2008-2009 one focus of BSL's technical efforts went toward maintaining and repairing existing instrumentation, stations, and infrastructure. While expanding the data acquisition network continues to be a long term goal of BSL, it is equally important to assure the integrity of the established network and preserve data quality.
YBH: The BSL has operated instruments at the YBH observatory in Yreka, California since June of 1993. All instrumentation and telemetry equipment is located within the long-abandoned mine. A steel door bars the entrance; recording instruments and telemetry equipment are located 25 meters beyond that door, with the seismometers approximately 25 meters beyond them. In addition to BSL seismometers (see Table 3.2), the YBH observatory includes an STS-2 seismometer and telemetry equipment as part of the CTBTO, as well as GPS equipment for the BARD array. In 1993 when the site was developed, wooden shoring was added within the adit to add support to the original mine entrance. During the past year, it was discovered that some of those timbers had rotted and collapsed. BSL engineers drew up plans and specifications for replacing the timbers. Working with UC Berkeley physical plant, a general engineering contractor was hired in Yreka to remove the rotted material and reshore the area. The reshoring work at the site was completed in March, 2009. BSL engineers visited the site three times to plan, oversee, and accept the work performed by the contractor. During one trip, the BSL engineer replaced the Ashtech GPS receiver with a Trimble NetRS receiver. The Trimble receiver features Ethernet communication and has onboard memory, making it more robust.
JRSC: The equipment at station JRSC is operated and maintained by the BSL on behalf of Stanford University. In March of 2009, equipment at the JRSC site suffered from what appear to be the effects of a nearby lightning strike. The phone company's digital network interface and BSL's frame relay access device (FRAD) were damaged as a result. Several visits to the site were necessary to restore telemetry to Berkeley. At about the same time it was noted the Metrozet TSA-100 strong motion sensor was not responding to ground motion. Investigation revealed that BSL engineers had powered the sensor with the incorrect voltage. The TSA-100 requires 12 V DC power; as the JRSC site had one of the first generation Quanterra Q680 stations, it only had 24 V circuits available. As installed, the TSA-100 instrument ran off of 24 V with no problem for nearly a year. It is not completely clear whether the instrument ultimately failed due to the incorrect voltage or whether the lightning strike caused the failure. In either case, Metrozet has agreed to repair or replace the instrument under warranty. Reinstallation of the strong motion sensor at station JRSC is awaiting the return of the sensor from Metrozet.
JCC: The BSL has operated the station JCC at Bayside, CA, since April of 2001. During power outages caused primarily by winter storms, the on site batteries no longer support station operation for at least three days, but only approximately 30 hours after the AC power fails. During a site visit, BSL engineers replaced batteries installed in 2001. They noted that access to the vault was somewhat restricted due to brush overgrowing the road. It may be necessary to remove the brush at some point. Also during this visit, the STS-2 seismometer was replaced with an instrument that was pre-calibrated using a step test procedure in Berkeley. The STS-2 that was removed from JCC was returned to Berkeley, where a step test calibration was performed. The 17 year old instrument was found to be within 1% of the factory calibrated sensitivity.
FARB: The BSL has operated instrumentation on SE Farallon Island continuously since 1994. Initially a GPS receiver was installed, and it was augmented with broadband and strong motion seismic instruments in 1996. Because of the highly corrosive marine environment, the radio telemetry antennas have been replaced every two years. Continuous seismic and GPS telemetry from the island is achieved using redundant 900 MHz and 2.4 GHz digital radio transceivers. The 900 MHz radio link connects the Farallon Island site through the Golden Gate to the Space Science building on the hills of the Berkeley campus. When this radio link became unstable during the past winter, BSL engineers found that the antennas on the Space Science building had been moved. After several meetings, the BSL antennas were restored, bringing the 900 MHz radio link to the Farallons up again. The 2.4 GHz link operates from the island to the University of California Medical Science building in San Francisco. From San Francisco, a frame relay circuit completes that data link to Berkeley. Over the years, the BSL has come to provide technical support for all radios on the Farallons. During February of 2009, BSL engineers met with representatives from the US Fish and Wildlife Service and the California Academy of Science regarding installation of additional high bandwidth radio links between the mainland and the island. The California Academy of Science wishes to establish a web camera on the Farallons, and they have offered to provide the BSL with data telemetry from the island to once their link is established. The BSL may pursue this after the new radio link has demonstrated its ability to survive the particularly harsh winter weather on the island.
GASB: During the last week of May in 2009, a massive lightning strike damaged equipment at GASB. BSL engineers subsequently replaced the Quanterra data logger, the telemetry radio transceiver, and the power supply. All of these devices were behind industrial lightning and surge protectors. Trees within 50 meters of the seismic vault bear evidence of the nearby lightning strikes.
SAO: For several years, we have been upgrading the infrastructure at SAO. In May of 2009, the door to the seismic seismic vault at SAO was smashed by vandals. BSL engineers repaired the door, replaced the lock, and added a steel plate to completely cover the exterior of the existing door. General site clean-up included removal and disposal of an office trailer that had been on the site since the mid 1970's, as well as cabling strung through the trees by graduate students at about the same time.
MCCM: Twice during the spring of 2009, the Quanterra data logger at MCCM became unresponsive or died. On one of these occasions, the VSAT equipment provided by USNSN was also in a hung state. The other time, the data logger's state of health circuit board was not working and the external clock antenna was damaged; lightning is suspected to have played a role in both outages. In the course of routine network maintenance, BSL engineers replaced half of the batteries installed when the station was commissioned in 2005.
KCC: KCC is arguably the BSL's most remote station, located in a Southern California Edison water tunnel deep in the granites of the Sierra Nevada. BSL engineers installed a new Metrozet E300 seismometer electronics package at station KCC in October of 2008. These electronics replace the original, factory-built STS-1 electronics, and offer remote calibration and control of the sensors. Problems were observed with the seismometer calibration sequence using the E300, although the calibration is believed to be correct. It appears that ground loops among the installed instrumentation interfer with the E300 functionality. The Kinemetrics FBA-23 strong motion sensor at KCC has a single-ended output, and this type of sensor has been known to cause ground loops. BSL plans to replace all remaining FBA-23 instruments installed at BDSN stations with differential, and more sensitive strong motion sensors. A return trip to do this at KCC is planned.
MNRC: The BSL has operated the seismic observatory at the UC McLaughlin Mine Reserve (MNRC) since 2003. Data from the site are telemetered via digital radio to the summit of Mount Saint Helena and relayed from there to the California Department of Forestry and Fire command center in Napa. In 2008, a new 100 meter tall radio tower was constructed, and during the summer of 2009 the building at its base was completed. BSL engineers made three trips to the site in the past year to reposition antennas in order to maintain telemetry from the MNRC site as construction of the new tower progressed.
WENL: The seismic station at Wente Vineyards (WENL) is located at the rear of an adit that is used to age wine. To get clear view of the sky, the GPS antenna used to drive the data logger clock is located approximately 150 meters from the equipment. The antenna has high gain, and the coaxial cable is low loss to support the long distance. During the past year, the external clock reference developed problems. BSL engineers replaced the high gain antenna when clock signals from the GPS satellites were no longer being received. The level of cultural noise at WENL has increased over the past several years, and we are searching for a suitable replacement site.
HATC: The seismic station HATC is located at the UC radio astronomical observatory at Hat Creek, California. The seismic site takes advantage of an existing high speed data link between Hat Creek and the Berkeley Campus. Seismic instruments at HATC are powered by solar panels. During the fall of 2008, BSL engineers increased the size of the solar panel array in anticipation of shorter daylight hours during the winter.
CVS: The BSL station at CVS is located in the rear of a adit used for aging wine at the Moon Mountain Vineyard, Sonoma, California. During 2008, the winemaker at Moon Mountain brought to our attention the possibility that mold growing in the tunnel, and specifically growing on the plastic instrument case and insulating foam used over the seismometers, could contaminate the wine during the aging process. Although the wine is aged in oak barrels, the mold can taint its taste. We were asked to remove all plastic, wood, and foam from the adit. The BSL used this opportunity to upgrade the entire installation at CVS. The STS2 and FBA were removed, as were the data logger, telemetry equipment, power supplies, and batteries. A new steel instrument enclosure was installed and now houses a new power supply, batteries, and data logger. The old foam covering for the seismometers was replaced with new material and covered with a metal container.
MOD: The STS1 seismometers were removed from MOD, so that their electronics could be refurbished, as they were exhibiting reduced sensitivity, increased noise, and non-linear behavior. An STS2 was installed temporarily. The STS1 sensors were returned to Berkeley. Their hinges and connectors are being replaced, and the electronics refurbished. These instruments will be used in testing as part of the NSF funded STS1 development. We expect to return the STS1 seismometers to MOD in 2010.
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). The project has been described in detail in BSL annual reports since 2002 and in several publications (e.g. Romanowicz et al., 2003, 2006).
The MARS observatory (Figure 3.5, http://www.mbari.org/mars/) comprises a 52 km electro-optical cable that extends from a shore facility in Moss Landing out to a seafloor node in Monterey Bay (Figure 3.5). The cable was deployed in the spring of 2007, and node installation was completed in November 2008. It now can provide power and data to as many as eight science experiments through underwater electrical connectors. MOBB, located 3km from the node, is one of the first instruments to be connected to the cable. The connection was established on February 28, 2009, through an extension cable installed by the ROV Ventana, with the help of a cable-laying toolsled. The data interface at the MARS node is 10/100 Mbit/s Ethernet, which can directly support cables of no more than 100 m in length. To send data over the required 3 km distance, the signals pass through a Science Instrument Interface Module (SIIM) at each end of the extension cable (Figure 3.6. The SIIMs convert the MARS Ethernet signals to Digital Subscriber Line (DSL) signals, which are converted back to Ethernet signals close to the MOBB system. Power from the MARS node is sent over the extension cable at 375 VDC, and then converted to 28 VDC in the distal SIIM for use by the MOBB system. The connection to the MARS node eliminates the need for periodic exchange of the battery and data package using ROV and ship. At the same time, it allows us to acquire seismic data from the seafloor in real time (Romanowicz et al., 2009).
The electronics module in the MOBB system has been refurbished to support the connection to the MARS observatory. The low-power autonomous data logger has been replaced with a PC/104 computer stack running embedded Linux. This new computer runs an Object Ring Buffer (ORB), whose function is to collect data from the various MOBB sensors and forward it to another ORB running on a computer at the MARS shore station. There, the data are archived and then forwarded to a third ORB running at the UC Berkeley Seismological Laboratory. The Linux system acquires data (via RS232) from the Guralp digitizer included in the seismometer package, data (via ethernet) from a Q330 Quanterra 24 bit A/D converter which digitizes data from the DPG, and polls and receives data (via RS232) from the current meter. The data are available through the NCEDC. Procedures to include the MOBB data in the Northern California real time earthquake processing are under development.
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, Taka'aki Taira 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 section. MOBB is a collaboration between the BSL and MBARI, involving Barbara Romanowicz, Bob Uhrhammer, and Doug Neuhauser from the BSL, and Paul McGill from MBARI. The MBARI team also has included 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 development of the interface for connection to the MARS cable is funded by NSF/OCE grant #0648302.
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