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 3.1 and Table 3.1). This 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.

The network upgrade and expansion initiated in 1991 has continued, and it has grown from the original 3 broadband stations installed in 1986-87 (BKS, SAO, MHC) to 27 stations in 2004, including the ocean-bottom seismometer in Monterey Bay. One new station was added in the past year (GASB).

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 at existing stations.

Future expansion of our network 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.

Figure 3.1: Map illustrating the distribution of operational (filled squares), planned (open squares), and closed (grey squares) BDSN stations in northern and central California. The open squares (except for the one labelled GASB) indicate sites developed in collaboration with USArray.
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BDSN Overview

Twenty-five of the BDSN sites are equipped with 3 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. Data from all BDSN stations 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 data loggers ensures that the BDSN has the capability to record the full range of earthquake motion for source and structure studies. Table 3.2 lists the instrumentation at each site.

Most BDSN stations have Streckeisen three-component broadband sensors (Wielandt and Streckeisen, 1982; Wielandt and Steim, 1986). Guralp CMG-3T downhole broadband sensors contributed by LLNL are deployed in post-hole installations at BRIB and FARB. The strong-motion instruments are Kinemetrics FBA-23 or FBA-ES-T with $\pm$ 2 g dynamic range. The recording systems at all sites are either Q730, Q680, Q980 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, 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 3.3). In addition to the 6-channels of seismic data, signals from thermometers and barometers are recorded at nearly every site (Figure 3.2).

Figure 3.2: 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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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 data loggers, additional services such as FTP and telnet to the data loggers, data transmission to multiple sites, and the ability to communicate and transmit data from multiple instruments such as GPS receivers and/or multiple data loggers at a single site. Today, 23 of the BDSN sites use frame-relay telemetry for all or part of their communications system.


Table 3.1: Currently operating stations of the Berkeley Digital Seismic Network. 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 39.65 -122.72 TBD TBD 2004/06 - Alder Springs
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
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
POTR BK 38.2026 -121.9353 20.0 6.5 1998/02 - Potrero Hill, Fairfield
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
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 06/30/2003. Every BDSN station consists of collocated broadband and strong-motion sensors, with the exception of PKD1, RFSB and SCCB which are strong-motion only, with a 24-bit Quanterra data logger and GPS timing. 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, R - radio, Mi - microwave, POTS - plain old telephone line, NSN - USGS NSN satellite link, None - no telemetry at this time. An entry like R-Mi-FR indicates multiple telemetry links, in this case, radio to microwave to frame relay.
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       POTS    
CMB STS-1 FBA-23 Q980 X X Baseplates FR/NSN 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     TBD    
HOPS STS-1 FBA-23 Q980 X X Baseplates FR X  
HUMO STS-2 FBA-ES-T Q4120 X     NSN 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  
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 NSN 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  
POTR STS-2 FBA-ES-T Q4120 X X   FR X  
RFSB   FBA-ES-T Q730       FR    
SAO STS-1 FBA-23 Q980 X X Baseplates, EM FR/NSN X  
SCCB   FBA-ES-T Q730   X   FR    
WDC STS-2 FBA-23 Q980 X     FR/NSN X  
WENL STS-2 FBA-23 Q4120 X     FR    
YBH STS-1 & STS-2 FBA-23 Q980 X X Baseplates FR X  


As described in Chapter 8, 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 2 and 9). As part of routine quality control (Chapter 8), power spectral density analyses are performed weekly and Figure 3.3 shows a summary of the results for 2003-2004. The occurrence of a significant teleseism also provides the opportunity to review station health and calibration. Figure 3.4 displays BDSN waveforms for a $M_{w}$ 6.8 deep focus earthquake in the Primor'ye, Russia region on July 27, 2003.

BDSN data are archived at the Northern California Earthquake Data Center. This is described in detail in Chapter 10.

Figure 3.3: PSD noise analysis for BDSN stations, by channel, in the period range from 32-128 sec from 7/1/2003-6/30/2004. BRIB (situation in a shallow vault that is prone to tilting) and FARB (located on the Farallon Islands) stand out as sites with high noise levels. HUMO (located in an abandoned mine) stands out as an exceptionally quiet site.
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Figure 3.4: BDSN broadband vertical-component waveforms for a $M_{w}$ 6.8 deep focus earthquake (470 km) which occurred in the Primor'ye, Russia region on July 27, 2003. This earthquake was felt in Hokkaido amd Honshu, Japan. The waveforms were deconvolved to absolute ground velocity, 0.01-0.1 Hz band pass filtered, and plotted in order of increasing distance from HUMO at 64.9 degrees to PKD at 70.8 degrees. Shown are the P, pP, and sP body wave phases. Note that the body waves are highly similar across the BK network and that most noticeable diff erences are in the coda detail and the absolute amplitudes. This provides confirmation that the station transfer function and polarities are correct. The stations MNRC and POTR especially stand out in that their amplitudes are significantly larger than is observed at the other BDSN stations, owing primarily to their siting in the proximity of thick alluvial deposits which amplify the ground motions.
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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 dataloger type. Q4120s provide 100 sps and causal filtering; Q680/980s provide 80 sps and acausal filtering. The BH channels were changed from 20 to 40 sps this year as described below.
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 and PKD, 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, 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 in collabration with Dr. Frank Morrison. 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 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 3.1). 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.

2003-2004 Activities

USArray

As mentioned in Chapter 2, 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 includes 17 existing stations: CMB, CVS, FARB, HOPS, HUMO, JCC, JRSC, KCC, MNRC, MOD, ORV, PACP, PKD, POTR, WDC, WENL, and YBH as well as two sites currently under construction: GASB and MARC.

The 19 BDSN sites provide 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. This is discussed more extensively in Chapter 8.

In addition, the BSL is collaborating with USArray to identify other sites that may be suitable to become BDSN stations. During the past year, BSL staff have been working to identify 8 potential sites for USArray/BDSN instrumentation, many at UC reserves and field stations (shown in Figure 3.1). One of these sites is the Hastings Reserve.

The BSL identified the Hastings Biological Field Station as a potential site of interest over five years ago, but did not have the funding to proceed. Hastings is a biological field station of the University of California, located in the Carmel Valley. The occurrence of the 12/22/2003 San Simeon earthquake, 70 km to the SW, provided additional motiviation for establishing this station.

Bob Uhrhammer visited Hastings in April 2004 and met with Mark Stromberg, the reserve director. They identified two potential sites for broadband instrumentation. Bob Busby, the USArray field manager, made the final selection and the station was installed in July 2004 by a USArray field team.

In the coming year, BSL staff will be working to permit other sites of interest in northern and central California.

Station Maintenance

Given the remoteness of the off-campus stations, BDSN data acquisition equipment and systems have been designed, configured, and installed for both cost effectiveness and reliability. As a result, the need for regular station visits has been reduced. Most station visits are necessitated by some catastrophic failure. The 2003-2004 fiscal year was no exception, with the additional complication of a reduction in staff.

NSN VSAT modifications

The BSL cooperates with the US NSN on the following sites in northern California: SAO, CMB, WDC, MOD, and HUMO. At each of these sites, the NSN has provided a VSAT to support a communications link. The MOD and HUMO sites are sufficiently remote that the VSAT is the only communications link available.

In 2003, the US NSN began to replace the older VSAT systems and, in February 2004, the USGS turned off the original satellite system. Prior to the end of Feburary, BSL staff traveled to HUMO and MOD to work with USGS contractors on the installation of the new VSAT system. Fortunately, these two installations were completed just before the older system was turned off, avoiding the loss of communications.

Unfortunately, we have not completed the VSAT modifications at the three remaining sites. Hopefully this task will be completed during FY04/05, as the VSATs provide an important secondary communication link at these stations. At this time, data from the non-upgraded stations is provided to NEIC via the BSL data acquisition.

In May, the USGS contractors installed an NSN VSAT at McCone Hall. The replacement of the older VSAT restored the capability of the BSL to receive data directly from the satellite system, rather than over the Internet.

Problems with accelerometers

The San Simeon earthquake highlighted problems with the FBA-23s and Episensors at several BDSN sites. JRSC (FBA-23), MHC (FBA-23), WENL (FBA-23), and RFSB (Episensor) showed problems with the San Simeon recording (primilarly poor response to ground motions). Thus far, we have replaced the sensors at WENL and the JRSC sensor has been sent for repair.

PKD telemetry

At the time the station PKD was installed in 1996, continuous telemetry from the site was achieved by interconnection of a digital spread spectrum radio (900 MHz) with the frame-relay circuit at Carr Hill. Radios in this spectrum have the advantage of not requiring federal licensing or permits. The BSL installation in 1996 was the first use of such equipment in Parkfield. At least two other investigating groups in Parkfield subsequently installed similar radios, ultimately causing interference and a reduction in data bandwidth. In December of 2003, BSL and USGS engineers went to Parkfield to coordinate frequencies, align antennas, and replace and move radio equipment in order to minimize future interference. Over two days, the telemetry path from the PKD vault to the Carr hill site was redirected to a repeater site operated by UCSD. RF signal levels were tested and confirmed. In January of 2004 however, the signal levels on the new path had faded as much as 20 db, apparently due to the increased water absorbtion by vegetation within the direct line of site. During a January trip by BSL engineers, antennas were once again this time redirecting the data path directly to Carr Hill. Unfortunately, that solution was short lived as the signal level fell again faded more than 10 db in the following two weeks. During a third trip, BSL engineers installed a solar powered radio repeater. This solar powered radio repeater has continued to operate satisfactorily through the dry summer months. A replacement for this repeater is planned at a location with will further improve the radio signal level pending permission from the local landowner.

Other maintenance

At KCC, we replaced all the batteries, removing over 1600 lbs of worn out batteries.

The ownership of the POTR site has changed and we are in the process of negotiating with the new owner.

A landslide at WDC resulted in flooding in the tunnel and water entering the dome. As part of bringing the station back online, the dome was opened (for the first time in over 7 years) and the sensors were replaced.

An optoisolator and a DC-DC converter were installed at YBH to reduce the noise.

New Installations

In the past year, two installations were completed and one new site was started. The installations at PACP and MNRC were completed and a new site at Alder Springs was started. A fourth site, Marconi, is in the process of being permitted and installation will start soon.

Pacheco Peak

The Pacheco Peak site was installed in June 2003. In the initial installation, the seismometers were temporarily placed on the floor in the communications building. During 2003-2004, a pier and vault were constructed. The seismometers were relocated to the vault in September, 2003.

McLaughlin Mine

With the conclusion of mining operations, the McLaughlin Mine in Lake and Yolo counties will be managed as a UC Reserve by UC Davis. The site is on property owned and formerly operated by Homestake Mining Company as a surface gold mine. The site is located approximately 20 kilometers east of the town of Lower Lake, California in an area of Franciscan sandstone with volcanic precipitates forming the gold deposit.

Last year, a steel and concrete vault from a shipping container similar to those found at stations JCC, PKD, and HOPS was constructed. Power and telephone lines were trenched approximately 300 meters to the site. Because of the remoteness of the site, digital telephone data circuits are not available. During 2003-2004, BSL engineers permitted, designed, prefabricated and installed a two-hop wireless radio bridge to a State of California radio and microwave facility on Mt Saint Helena twenty-five kilometers away. From the Mt Saint Helena site, data are relayed to the California Department of Forestry and Fire Protection (CDF) command center in the Napa Valley, where a connection to the frame-relay network is made. A dial up connection is also available for data downloading or communicating with the McLaughlin Mine site.

Alder Springs

The Alder Springs site located approximately 35 kilometers west of the central valley town of Willows. Local geology is mostly serpentine and Franciscan. Previously, a short period observatory has been operated at the Alder Springs site by the California Department of Water Resources.

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 site is permit was provided by the US Forest Service, Mendocino National Forest.

Continuous telemetry is planned for the site. Again, the remote nature of the site will necessitate a combination of radios and digital circuits. Our initial investigations and efforts to relay the data via the same Mt Saint Helena radio connection as the McLaughlin Mine site proved impossible. We expect to achieve continuous telemetry in the second quarter of 2004-05. This site has been named GASB by the BSL.

Marconi

We permitted a site at the Marconi Conference Center, near Marshall, CA. The conference center is operated by the State of California. This site will be installed in collaboration with the USGS and will form part of the ANSS backbone network. Installation will take place in the fall of 2004.

MOBB: An Ocean Floor Broadband Station

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 permanent 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). In this context, evaluating the possibility of a posteriori noise deconvolution using auxiliary data (e.g. current meter, differential pressure gauge) as well as comparison with land based recordings (see section 18 in Chapter III). 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 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 is currently recording data autonomously (e.g. Romanowicz et al., 2003). Eleven "dives" involving the MBARI ship "Point Lobos" and ROV "Ventana" have so far taken place to exchange data loggers and battery packages. 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. Unfortunately, we are continuing to experience problems with the data from the Differential Pressure Gauge (DPG, Cox et al., 1984), which are crucial for the development and implementation of a posteriori noise deconvolution procedures to help counteract the large contribution of infragravity noise in the period range 20-200 sec (Figure 3.6).

Figure 3.5: Location of the MOBB station in Monterey Bay, California, against seafloor and land topography. The projected path of the MARS cable is indicated by the solid line.
map

Figure 3.6: Comparison of noise recorded at MOBB and 3 other stations of the BDSN network, on two days in 2002 when no significant earthquake signals were recorded: a "quiet day" (143,left), and a "stormy" day (350,right), as assessed by the mean wave height recordings at a nearby NOAA buoy, located in Monterey Bay. Spectra were calculated using 4 hours of data. The USGS high- and low-noise models for land stations are shown in black (Peterson, 1993). Increased noise levels for periods between 20 and 300 sec, are observed at MOBB on both quiet and stormy days, as well as at the island station FARB on the stormy day. The noise level at MOBB between 10 and 20 sec is comparable to the land station YBH, one of the quietest stations of the BDSN. Note how the height and also the width of the infragravity noise band increases on stormy days.
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With input from BSL staff, MBARI engineers are currently working on hardware and software developments needed to connect the MOBB sensors to the MARS (Monterey Accelerated Research System; http://www.mbari.org/mars/) cable, which is scheduled to be deployed in Fall 2005 (Figure 3.5). This will provide access to real-time, continuous seismic data from MOBB to be merged with the rest of the northern California real-time seismic system.

Acknowledgements

Under Barbara Romanowicz's general supervision, Lind Gee and Doug Neuhauser oversee the BDSN data acquisition operations and Bill Karavas is head of the engineering team. John Friday, Dave Rapkin, and Bob Uhrhammer contribute to the operation of the BDSN. Sierra Boyd has been responsible for the operation of the EM observatories. Bill Karavas, Bob Uhrhammer, and Lind Gee contributed to the preparation of this chapter.

The California Governor's Office of Emergency Services provided funding toward the development of sites MNRC, PACP, and GASB as part of the CISN.

MOBB is a collaboration between the BSL and MBARI, involving Barbara Romanowicz, Bob Uhrhammer, and Doug Neuhauser 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 funds from NSF/OCE and UC Berkeley. The MOBB seismometer package was funded by NSF/OCE grant #9911392.

References

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

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

Peterson, J. R., Observations and modeling of seismic background noise, U. S. Geological Survey Open File Report, 93-322, 94 pp., 1993.

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

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