Subsections


Berkeley Digital Seismic Network



Introduction

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 38.2 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.

Table 3.1: Stations of the Berkeley Digital Seismic Network currently operating. Each BDSN station is listed with its station code, network id, location, operational dates, and site description. The latitude and longitude (in degrees) are given in the WGS84 reference frame, and the elevation (in meters) is relative to the WGS84 reference ellipsoid. The elevation is either the elevation of the pier (for stations sited on the surface or in mining drifts) or the elevation of the well head (for stations sited in boreholes). The overburden is given in meters. The date indicates either the upgrade or installation time.
Code Net Latitude Longitude Elev (m) Over (m) Date Location
BDM BK 37.9540 -121.8655 219.8 34.7 1998/11 - Black Diamond Mines, Antioch
BKS BK 37.8762 -122.2356 243.9 25.6 1988/01 - Byerly Vault, Berkeley
BRIB BK 37.9189 -122.1518 219.7 2.5 1995/06 - Briones Reservation, Orinda
BRK BK 37.8735 -122.2610 49.4 2.7 1994/03 - Haviland Hall, Berkeley
CMB BK 38.0346 -120.3865 697.0 2 1986/10 - Columbia College, Columbia
CVS BK 38.3453 -122.4584 295.1 23.2 1997/10 - Carmenet Vineyard, Sonoma
FARB BK 37.6978 -123.0011 -18.5 0 1997/03 - Farallon Island
GASB BK 39.6547 -122.716 1354.8 2 2005/09 - Alder Springs
HAST BK 36.3887 -121.5514 542.0 3 2006/02 - Carmel Valley
HATC BK 40.8161 -121.4612 1009.3 3 2005/05 - Hat Creek
HELL BK 36.6801 -119.0228 1140.0 3 2005/04 - Miramonte
HOPS BK 38.9935 -123.0723 299.1 3 1994/10 - Hopland Field Stat., Hopland
HUMO BK 42.6071 -122.9567 554.9 50 2002/06 - Hull Mountain, Oregon
JCC BK 40.8175 -124.0296 27.2 0 2001/04 - Jacoby Creek
JRSC BK 37.4037 -122.2387 70.5 0 1994/07 - Jasper Ridge, Stanford
KCC BK 37.3236 -119.3187 888.1 87.3 1995/11 - Kaiser Creek
MCCM BK 38.1448 -122.8802 -7.7 2 2006/02 - Marconi Conference Center, Marshall
MHC BK 37.3416 -121.6426 1250.4 0 1987/10 - Lick Obs., Mt. Hamilton
MNRC BK 38.8787 -122.4428 704.8 3 2003/06 - McLaughlin Mine, Lower Lake
MOBB BK 36.6907 -122.1660 -1036.5 1 2002/04 - Monterey Bay
MOD BK 41.9025 -120.3029 1554.5 5 1999/10 - Modoc Plateau
ORV BK 39.5545 -121.5004 334.7 0 1992/07 - Oroville
PACP BK 37.0080 -121.2870 844 0 2003/06 - Pacheco Peak
PKD BK 35.9452 -120.5416 583.0 3 1996/08 - Bear Valley Ranch, Parkfield
RAMR BK 37.9161 -122.3361 416.8 3 2004/11 - Ramage Ranch
RFSB BK 37.9161 -122.3361 -26.7 0 2001/02 - RFS, Richmond
SAO BK 36.7640 -121.4472 317.2 3 1988/01 - San Andreas Obs., Hollister
SCCB BK 37.2874 -121.8642 98 0 2000/04 - SCC Comm., Santa Clara
SUTB BK 39.2291 -121.7861 252.0 3 2005/10 - Sutter Buttes
WDC BK 40.5799 -122.5411 268.3 75 1992/07 - Whiskeytown
WENL BK 37.6221 -121.7570 138.9 30.3 1997/06 - Wente Vineyards, Livermore
YBH BK 41.7320 -122.7104 1059.7 60.4 1993/07 - Yreka Blue Horn Mine, Yreka



Table 3.2: Instrumentation of the BDSN as of 06/30/2007. Except for PKD1, RFSB, SCCB and MOBB, each BDSN station consists of collocated broadband and strong-motion sensors, with a 24-bit Quanterra data logger and GPS timing. The stations RFSB and SCCB are strong-motion only, while MOBB has only a broadband sensor. Additional columns indicate the installation of a thermometer/barometer package (T/B), collocated GPS receiver as part of the BARD network (GPS), and additional equipment (Other), such as warpless baseplates or electromagnetic sensors (EM). The obs station MOBB also has a current meter and differential pressure gauge (DPG). The main and alternate telemetry paths are summarized for each station. FR - frame relay circuit, LAN - ethernet, Mi - microwave, POTS - plain old telephone line, R - radio, Sat - Commercial Satellite, VSAT - USGS ANSS satellite link, None - no telemetry at this time. An entry like R-Mi-FR indicates telemetry over several links, in this case, radio to microwave to frame relay. (*) During 2007-2008 the STS-1 at this station was replaced by an STS-2.
Code Broadband Strong-motion data logger T/B GPS Other Telemetry Dial-up  
BDM STS-2 FBA-23 Q4120 X     FR    
BKS STS-1 FBA-23 Q980 X   Baseplates FR X  
BRIB CMG-3T FBA-23 Q980   X Vol. Strain FR X  
BRK STS-2 FBA-23 Q680       LAN    
CMB STS-1 FBA-23 Q980 X X Baseplates FR X  
CVS STS-2 FBA-23 Q4120 X     FR    
FARB CMG-3T FBA-23 Q4120 X X   R-FR/R    
GASB STS-2 FBA-ES-T Q4120 X     R-FR    
HAST STS-2 FBA-ES-T Q330       R-Sat    
HATC STS-2 FBA-ES-T Q330       T-1    
HELL STS-2 FBA-ES-T Q330       R-Sat    
HOPS STS-1 FBA-23 Q980 X X Baseplates FR X  
HUMO STS-2 FBA-ES-T Q4120 X     VSAT X  
JCC STS-2 FBA-23 Q980 X     FR X  
JRSC STS-2 FBA-23 Q680       FR X  
KCC STS-1 FBA-23 Q980 X   Baseplates R-Mi-FR X  
MCCM STS-2 FBA-ES-T Q4120       VSAT    
MHC STS-1 FBA-23 Q980 X X   FR X  
MNRC STS-2 FBA-ES-T Q4120 X     None X  
MOBB CMG-1T   GEOSense     Current meter, DPG None    
MOD STS-1* FBA-ES-T Q980 X X Baseplates VSAT X  
ORV STS-1 FBA-23 Q980 X X Baseplates FR X  
PACP STS-2 FBA-ES-T Q4120 X     Mi/FR    
PKD STS-2 FBA-23 Q980 X X EM R-FR X  
RAMR STS-2 FBA-ES-T Q330       R-FR X  
RFSB   FBA-ES-T Q730       FR    
SAO STS-1 FBA-23 Q980 X X Baseplates, EM FR X  
SCCB   MetroZet Q730   X   FR    
SUTB STS-2 FBA-EW-T Q330       R-FR    
WDC STS-2 FBA-23 Q980 X     FR X  
WENL STS-2 FBA-23 Q4120 X     FR    
YBH STS-1 & STS-2 FBA-23 Q980 X X Baseplates FR X  


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. While maintenance and repair were an important focus of this year's efforts, we were also able to add five new stations as the USArray deployment left California. Considerable engineering and research activities were also involved in several projects to develop and test new instrumentation (see Section 7, Section 9, and Chapter 1, Section 34.). The project involving new electronics for the STS-1 seismometers, the E300, was completed, and we have deployed the beta version of the electronics for testing at several stations. It 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. As always, 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 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 both repairs and upgrades.

BDSN Overview

Twenty-nine 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, except MOBB, are transmitted to UC Berkeley using continuous telemetry. 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 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, FBA-ES-T or MetroZet accelerometers with $\pm$ 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).

Figure 3.3: Schematic diagram showing the flow of data from the sensors through the data loggers to the central acquisition facilities of the BSL.
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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. The occurrence of a significant teleseism also provides the opportunity to review station health and calibration. Figure 3.4 displays BDSN waveforms for a $M_{w}$ 7.7 deep focus earthquake in the Sea of Okhotsk region on July 5, 2008.

Figure 3.4: Long period waveforms recorded across BDSN from the deep $M_{w}$ 7.7 teleseism which occurred on July 5, 2008, in the Sea of Okhotsk at 53.888$^{\circ}$N, 152.869$^{\circ}$E. The traces are deconvolved to ground velocity, scaled absolutely, and ordered from top to bottom by distance from the epicenter. The highly similar waveforms recorded across the BDSN provide evidence that the broadband sensors other than the N component at BRIB are operating within their nominal specifications. The sensor at MOD is currently an STS-2, which is rotated by 90$^{\circ}$, so the N and E components are exchanged.
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BDSN data are archived at the Northern California Earthquake Data Center. This is described in detail in Section 6

Table 3.3: Typical data streams acquired at BDSN stations, with channel name, sampling rate, sampling mode, and the FIR filter type. SM indicates strong-motion; C continuous; T triggered; Ac acausal; Ca causal. The LL and BL strong-motion channels are not transmitted over the continuous telemetry but are available on the Quanterra disk system if needed. The HH channels are recorded at two different rates, depending on the data logger. Q4120s and Q330s provide 100 sps and causal filtering; Q680/980s provide 80 sps and acausal filtering.
Sensor Channel Rate (sps) Mode FIR
Broadband UH? 0.01 C Ac
Broadband VH? 0.1 C Ac
Broadband LH? 1 C Ac
Broadband BH? 20/40 C Ac
Broadband HH? 80/100 C Ac/Ca
SM LL? 1 C Ac
SM BL? 20/40 C Ac
SM HL? 80/100 C Ac/Ca
Thermometer LKS 1 C Ac
Barometer LDS 1 C Ac



Table 3.4: Typical MT data streams acquired at SAO, PKD, BRIB and JRSC with channel name, sampling rate, sampling mode, and FIR filter type. C indicates continuous; T triggered; Ac acausal.
Sensor Channel Rate (sps) Mode FIR
Magnetic VT? 0.1 C Ac
Magnetic LT? 1 C Ac
Magnetic BT? 40 C Ac
Electric VQ? 0.1 C Ac
Electric LQ? 1 C Ac
Electric BQ? 40 C Ac


Electromagnetic Observatories

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 38.2). 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. 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. Since 2004, new electromagnetic instrumentation has been installed at various Bay Area stations in conjunction with Simon Klemperer at Stanford University. Sensors are installed at JRSC, MHDL and BRIB.

2007-2008 Activities

USArray

When the USArray deployment began in Northern California, the BSL contracted with IRIS to contribute data from 19 BDSN stations. The stations were CMB, CVS, FARB, GASB, HOPS, HUMO, JCC, JRSC, KCC, MCCM, MNRC, MOD, ORV, PACP, PKD, POTR, WDC, WENL, and YBH. In the fall of 2007, the USArray pulled out equipment from its temporary sites. No data from the BDSN was sent to USArray after November 2007. For the USArray, the BSL modified the data loggers to change the BH sampling rate from 20 Hz to 40 Hz, a sampling rate which we continue to use. During the station installation phase in Northern and Central California, the BSL collaborated with USArray to identify and permit sites that might be suitable as BDSN stations. Several were located at UC reserves and field stations. Data from these sites (Figure 38.2) were sent directly to the BSL as well as to the Array Network Facility and used in routine analysis to assess their performance. As the USArray left, we retained eight of the temporary sites (HAST, HATC, HELL, P01C, RAMR, S04C, SUTB and V03C). BSL engineers contacted the landowners prior to IRIS's departure. They received permission and made arrangements to continue operating stations at these sites. Because the overall objectives of the USArray deployment differ from the BSL's, their sites' construction and infrustructure are also different. As each station was reinstrumented, BSL engineers made a special effort to minimize or eliminate water that accumulated in the vaults/pits from condensation. Five of the sites have now been reinstrumented (see below). All of these sites operate using solar power, and are equipped with Q330 data loggers and STS-2 seismometers. The strong motion sensor is either a Kinemetrics EPISensor or Metrozet TSA 100 accelerometor. Continuous data telemetry to Berkeley has been achieved from all sites using a variety of methods.

Station Installation, Upgrades, Maintenance and Repairs

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, the broadband seismometers installed by BSL are of 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 2007-2008 one focus of BSL's technical efforts went toward maintaining and repairing existing instrumentation, stations and infrastructure. In addition, equipment was installed at five former USArray stations. While expanding the data acquisition network continues to be a long term goal of BSL, it is equally important to assure integrity of the established network and preserve data quality.

RAMR: Ramage Ranch, San Luis Obispo County, CA This former USArray site is on private property at the Ramage Ranch west of Paso Robles, California. Seismic equipment was reinstalled in September, 2007. The site required a number of visits, however, to develop engineering solutions to improve the USArray vaults. At RAMR the vault is a 1.5 meter corregated plastic culvert with a plastic lid set vertically into the native limestone. The lid is covered with soil and must be shoveled free each time entry is desired. Both the STS-2 and the strong motion sensor sit on the bottom of the vault along with a pump to remove accumulating water. The data logger, telemetry radio, batteries, and solar charge controller sit on a shelf of foam insulation above the seismometers. The telemetry antenna, external clock antenna and solar panel are mounted on a mast 10 meters from the vault. The cables pass through a buried conduit. As it is built, condensation forming in the conduit and filling it eventually drains into the vault and settles at the bottom. Within the vault, moisture also condensed and dripped from the underside of the lid. This water vapor was present year round - even during the rain free summer months. The USArray seismometers were continuously wet and often standing in about 50 mm of water. The sump pump could not remove water below this level. Fearing long-term damage from corrosion, BSL engineers did not reinstall seismometers until the accumulated water vapor had been removed from the vault and provisions made to prevent condensation from forming. In the original construction, the sole connection of the vault to the outside air was the cable conduit containing cables. BSL engineers emptied more than twenty liters of water from the conduits and pulled a 4 mm tube from inside the vault to the top of the mast. Next a ``tee'' section was added to the mast and the cables routed out one leg of the tee together with the newly installed tube. The area around the cables and tube was carefully plugged with expanding foam. A solar vent was added to the remaining section of the tee. In the newly configured ``tube within a conduit'', a restricted and controlled amount of outside air is continuously pulled through the tubing into the vault by the suction created by the solar vent. The air is exhausted during daylight hours by the solar vent. Water vapor does not condense on the underside of the lid. The air exchange is at a rate beyond the nominal bandwidth of the seismometers. BSL engineers returned to the site several times after the instruments were installed in order to optimize the solar panel, trim newly grown brush from the solar panel and telemetry antenna, and monitor the success of the vent system. Engineers also replaced the power system for the receiving radio at the frame relay drop.

SUTB: Sutter Buttes, Butte County, CA BSL engineers reinstalled instrumentation at the former USArray site at SUTB in April and May 2008. The site is located on private land north of the BARD-GPS site at Sutter Buttes. Continuous telemetry is achieved via digital radio telemetry relay to the GPS site atop Sutter Buttes, and onward to the frame relay circuit at station ORV. As described at RAMR, BSL engineers installed a solar powered ventilation system to eliminate condensation within the vault. Engineers also relocated the mast supporting the solar panel and radio antennas from beneath the canopy of an oak tree. The radio link remains problematic with remote troubleshooting required regularly.
HATC: Hat Creek Observatory, Lassen County, CA Instrumentation was reinstalled at the former USArray site at Hat Creek in April of 2008. The site is located on property owned by the University of California within the boundaries of the radio telescope array. Data are telemetered continuously from the site via the Observatory's T-1 line back to Berkeley. The support and cooperation of the UCB Astronomy department merits special mention.

HAST: Hastings Reserve, Monterey County, CA BSL engineers reinstalled instrumentation in the USArray vault at the Hastings Reserve in March of 2008. The site is located on property owned by the University of California system and operated as a biological field station (http://www.hastingsreserve.org). As at RAMR, BSL engineers installed solar ventilation at HAST to eliminate condensation within the vault. Telemetry from the site is accomplished via digital radio link to the University operated satellite link.

HELL: Hellweg Property, Fresno County, CA BSL reinstalled instrumentation in the USArray vault on property owned by Peggy Hellweg of the BSL in March of 2008. Telemetry from the site is accomplished via digital radio link and leased commercial satellite internet. As at RAMR, BSL engineers installed solar ventilation at HELL to eliminate condensation within the vault.

V03C: Fort Hunter-Liggett, Monterey County, CA The USArray site V03C of interest to the BSL is located on federal property at Fort Hunter-Liggett in Monterey County. This military base is administered by the US Army Corp of Engineers. USArray initially paid a substantial permitting fee to receive permission to occupy the site. BSL has indicated to the Corp of Engineers that we would be taking over operation of the site, and as a member of the IRIS consortium, have already paid the necessary permit fee. Our proposal appears to have been well received, and the permit transfer is currently being processed. We expect that the site will be reinstrumented with the 2008 calender year.

WENL: The BSL station WENL began operating in 1997. The equipment is installed in a high humidity adit used for storing and aging wine. BSL engineers replaced cables and the STS-2 seismometer this year after a reduction in the instrument's sensitivity (signal levels) was observed. Since WENL was installed, growth and development at the winery caused increases in the background noise levels over the past several years. A search for a suitable replacement site has begun.

HOPS: The BDSN station at Hopland, California, has been operating since October, 1994. The station is located approximately 100 miles northwest of Berkeley. In the summer of 2007, BSL engineers temporarily removed the control electronics for the STS-1 seismometers at HOPS. The external connectors on the electronics were found to have corroded sufficiently that currents leaked from pin-to-pin. Under magnification, the electronics were also found to have white ``fuzz'' growing on individual components. The resultant electrical leakage can reduce the seismometer's response to ground movement or even completely stop it. The electronics were thoroughly cleaned in an alchohol solution, and all connectors were replaced. When the cleaned electronics were replaced at HOPS, a calibration pulse was initiated using the factory electronics. The data were used to calculate the responses of the instruments. Then, the newly developed E300 electronics were substituted. The seismometers were run with the E300 control electronics for six weeks, after which the original electronics were reinstalled. The development and testing of MetroZet E300 electronics are described more fully in Section 9

KCC: At station KCC (Kaiser Creek California) BSL engineers removed the STS-1 seismometers during 2006-2007 and installed an STS-2, an instrument consistent with the specifications of the TA. This provided the opportunity to use the three STS-1 components at Berkeley's Byerly Vault in the STS-1 electronics upgrade program. In November 2007, the STS-1 seismometers were reinstalled at KCC. When the STS-1 seismometers were reinstalled at KCC, normal leveling and orientation procedures were followed. The prototype E300 electronics were also installed and the calibration features of the new electronics were exercised while the BSL engineers were on site. The calibration features could not be remotely activated once the engineers returned to Berkeley. Some grounding issue affecting the network connection is thought to be the reason. The network connection to the seismometer control E300 prototype has not been resolved at this time. It is, however, convenient to have the E300 electronics for the STS-1 seismometers installed at this site, as it allows remotely operated recentering.

MCCM: Continuous data telemetry from the station MCCM is achieved using VSAT equipment supplied by ANSS. During 2007, engineers from BSL installed additional hardware so that the VSAT system could be re-booted remotely if it should hang up or some other failure should occur. BSL also received permission from the California State Park system and the California Department of Forestry and Fire (CDF) to install two digital radio repeaters so that data from MCCM can be relayed to Berkeley by means other than the VSAT. We are currently awaiting specific siting instructions from the CDF on the radio tower at St Helena.

JRSC: The equipment at station JRSC is operated and maintained by BSL on behalf of Stanford University. In April of 2008, the strong motion FBA-23 was replaced with a MetroZet model TSA-100S sensor. The replacement sensor is plug compatible with the other strong motion sensors within the BDSN network. Additionally, the removed sensor did not provide the differential output that the Quanterra data logger expects. This incompatibility manifests itself in the form of ground loops and high instrument noise. The replacement TSA-100A sensor was purchased and provided by Stanford.

MHC: In late 2007, the strong motion Episensor at station MHC began to exhibit an offset on the east component. This is usually consistent with a sensor problem. Although the engineers from BSL installed a replacement sensor, the same symptoms continued during the next month. A second trip to the site revealed that the cable between the data logger and the sensor had become so stressed that an individual wire had disconnected at the back of the connector shell. The connector was repaired onsite. Additionally, BSL engineers proactively replaced the BARD GPS receiver which had been operating continuously since 1996. These recievers have been known to lose their software when their internal battery dies. Repair and upgrade of these receivers is described elsewhere in this publication.

MHDL and OXMT: The BSL equipment at MHDL and OXMT is co-located with USGS instruments as part of the miniPBO network. BSL engineers developed a scheme to isolate power to all instruments. The scheme involves separate AC-DC power supplies for each of the six instrument sets at the site. BSL engineers replaced several of the power supplies at each of the sites during 2007-2008 that had been damaged by mice infestation.

OHLN: The BSL equipment at OHLN is co-located with USGS instruments as part of the miniPBO array. Power to the site is provided by the local school district. Several times during the year, maintenance workers at the school inadvertently cut power to the seismic site. Power was always restored after BSL personnel contacted the school authority.

FARB: BSL has operated instrumentation on SE Farallon Island continuously since 1994. Beginning initially with a GPS receiver, broadband seismic instruments were added 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 link operates from the island, through the Golden Gate, to the hills above the Berkeley campus. 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 the data link to Berkeley. In the fall of 2007, BSL engineers made several trips to the island to replace and realign the antennas. During the same trips, the BSL engineers enabled digital radios for the use and benefit of the USFWS and the biologist stationed there. This link provides both data and VOIP services to the inhabitants of the island. BSL engineers also replaced all of the receiving antennas on the San Francisco end of links.

The Monterey Bay Ocean Bottom Seismic Observatory (MOBB)

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 offshore in Monterey Bay, with the help of MBARI's ``Point Lobos" ship and ROV ``Ventana" (Figure 3.5). 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 has been recording data autonomously ever since (e.g. Romanowicz et al., 2003). It comprises a three 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. Twenty-three ``dives'' involving the MBARI ship ``Point Lobos'' and ROV ``Ventana'' have so far taken place to exchange data loggers and battery packages during the time period 04/10/02 to 06/30/08. 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 Systems Ltd. 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.

Figure 3.5: Location of the MOBB station in Monterey Bay, California, against seafloor and land topography. The path of the MARS cable is indicated by the solid line.
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The MOBB station is located close to the path of the MARS cable (Figure 3.5) which was deployed in the spring of 2007. 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 recently funded NSF project. Work on this project commenced in the summer of 2007. Installation is planned in spring 2009.

Acknowledgements

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 section. The California Governor's Office of Emergency Services and the Federal Emergency Management Agency provided funds for the istrumenation installed at the new stations HAST, HATC, HELL, RAMR and SUTB. 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.

References

Cox, C., T. Deaton and S. Webb, A deep-sea differential pressure gauge, J. Atm. Ocean. Tech., 1, 237-245, 1984.

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.

Murdock, J., and C. Hutt, A new event detector designed for the Seismic Research Observatories, USGS Open-File-Report 83-0785, 39 pp., 1983.

Romanowicz, B., D. Stakes, J. P. Montagner, P. Tarits, R. Uhrhammer, M. Begnaud, E. Stutzmann, M. Pasyanos, J.F. Karczewski, and S. Etchemendy, MOISE: A pilot experiment towards long term sea-floor geophysical observatories, Earth Planets Space, 50, 927-937, 1999.

Romanowicz, B., D. Stakes, R. Uhrhammer, P. McGill, D. Neuhauser, T. Ramirez, and D. Dolenc, The MOBB experiment: a prototype permanent off-shore ocean bottom broadband station, EOS Trans. AGU, Aug 28 issue, 2003.

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Stutzmann, E., J.P. Montagner et al., MOISE: a prototype multiparameter ocean-bottom station, Bull. Seism. Soc. Am., 81, 885-902, 2001.

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