BDSN Overview

Twenty-four of the BDSN sites are equipped with 3 component broadband seismometers and strong-motion accelerometers, and a 24-bit digital data acquisition system or datalogger. Two additional sites (RFSB and SCCB) consist of a strong-motion accelerometer and a 24-bit digital datalogger. The ocean-bottom station MOBB is equipped with a 3 component broadband seismometer. Data from all BDSN stations, except MOBB, are transmitted to UC Berkeley using continuous telemetry. In order to insure against data loss during utility disruptions, each site has a 3-day supply of battery power and is accessible via a dialup phone line. The combination of high-dynamic range sensors and digital dataloggers ensures that the BDSN has the capability to record the full range of earthquake motion for source and structure studies. Table 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 dataloggers, with 3, 6, 8, or 9 channel systems. The Quanterra dataloggers employ FIR filters to extract data streams at a variety of sampling rates. In general, the BDSN stations record continuous data at .01, 0.1, 1.0, 20.0 or 40.0, and 80 or 100 samples per second, although some sites send triggered data at the highest sampling rate using the Murdock, Hutt, and Halbert event detection algorithm (Murdock and Hutt, 1983) (Table 3.3). In addition to the 6 channels of seismic data, signals from thermometers and barometers are recorded at nearly every site (Figure 3.3).

Figure 3.3: Schematic diagram showing the flow of data from the sensors through the dataloggers to the central acquisition facilities of the BSL.
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\epsfig{file=dataflow.eps, width=10cm}\end{center}\end{figure*}

In parallel with the upgrade of the broadband network, a grant from the CalREN Foundation (California Research and Education Network) in 1994 enabled the BSL to convert data telemetry from analog leased lines to digital frame-relay connections. The frame-relay network uses digital phone circuits that can support 56 Kbit/s to 1.5 Mbit/s throughput. Since frame-relay is a packet-switched network, a site may use a single physical circuit to communicate with multiple remote sites through the use of ``permanent virtual circuits". Frame Relay Access Devices (FRADs), which replace modems in a frame-relay network, can simultaneously support multiple interfaces such as RS-232 async ports, synchronous V.35 ports, and ethernet connections. In practical terms, the upgrade to frame relay communication provides faster data telemetry between the remote sites and the BSL, remote console control of the dataloggers, additional services such as FTP and telnet to the dataloggers, data transmission to multiple sites, and the ability to communicate and transmit data from multiple instruments such as GPS receivers and/or multiple dataloggers at a single site. Today, 23 of the BDSN sites use frame-relay telemetry for all or part of their communications system.


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 39.6547 -122.716 1354.8 2 2005/09 - 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
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
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 06/30/2007. Except for PKD1, RFSB, SCCB and MOBB, each BDSN station consists of collocated broadband and strong-motion sensors, with a 24-bit Quanterra datalogger and GPS timing. The stations PKD1, 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, R - radio, Mi - microwave, POTS - plain old telephone line, 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 part of 2006-2007 the STS-1s at these two stations were replaced by STS-2s
Code Broadband Strong-motion datalogger 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 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    
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  
RFSB   FBA-ES-T Q730       FR    
SAO STS-1 FBA-23 Q980 X X Baseplates, EM FR X  
SCCB   MetroZet Q730   X   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  


As described in Section 3.7., 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 3.2. and 3.8.). As part of routine quality control (Section 3.7.), power spectral density (PSD) analyses are performed weekly. Figure 3.4 shows a summary of the results for 2006 in comparison with other broadband stations operating in Northern California.

The occurrence of a significant teleseism also provides the opportunity to review station health and calibration. Figure 3.5 displays BDSN waveforms for a $M_{w}$ 8.1 deep focus earthquake in the Solomon Islands region on April 1, 2007.

Figure 3.4: PSD noise analysis for vertical components of the broadband stations of the BK, NC and TA networks in Northern California, in the period range from 32-128 sec for the interval 1/1/2006-12/31/2006. The BK and TA stations have much lower noise levels than the NC stations because of the sensors. 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. KCC is located in a overflow tunnel near a dam. When the water is running, it has high noise levels. HUMO (located in an abandoned mine) stands out as an exceptionally quiet site. The vertical lines indicate the average signal levels of events with $M_{L}$ 2.5, 3.5 and 4.5, respectively.
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Figure 3.5: $L_{R}(Z)$ vertical component broadband waveforms recorded across BDSN from the $M_{w}$ 8.1 teleseism which occurred on April 1, 2007, in the Solomon Islands at 8.48$^{\circ}$S, 156.98$^{\circ}$E. The traces are deconvolved to ground motion, scaled absolutely, and ordered from bottom to top by distance from the epicenter. For reference, the vertical distance between the traces is equivalent to 500 $nm/s^{2}$. The highly similar waveforms recorded across the BDSN provide evidence that the broadband sensors other than BDM are operating within their nominal specifications.
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\epsfig{file=teles.eps, width=12cm}\end{center}\end{figure*}

BDSN data are archived at the Northern California Earthquake Data Center. This is described in detail in Section 3.6..


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 dataloger type. Q4120s 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 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




Subsections

Berkeley Seismological Laboratory
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