NHFN Overview

The five MPBO sites have 3-component borehole geophone packages. All the remaining HFN sites have six-component borehole sensor packages. The packages were designed and fabricated at LBNL's Geophysical Measurement Facility by Don Lippert and Ray Solbau, with the exception of site SFAB. For the HFN sites, three channels of acceleration are provided by Wilcoxon 731A piezoelectric accelerometers and three channels of velocity are provided by Oyo HS-1 4.5 Hz geophones. Velocity measurements for the MPBO sites are provided by Mark Products L-22 2 Hz geophones (Table 5.2). The 0.1-400 Hz Wilcoxon accelerometers have lower self-noise than the geophones above about 25-30 Hz, and remain on scale and linear to 0.5 g. In tests performed in the Byerly vault at UC Berkeley, the Wilcoxon is considerably quieter than the FBA-23 at all periods, and is almost as quiet as the STS-2 between 1 and 50 Hz.

Sensors are generally installed at depths of about 100 m, but several sites have sensors emplaced at depths of over 200 m and the Dumbarton bridge sites have sensors at multiple depths (Table 5.1). During initial stages of the project, the NHFN sensors provided signals to on-site Quanterra Q730 and RefTek 72A-07 data loggers.

Today, twelve of the NHFN sites currently have Quanterra data loggers with continuous telemetry to the BSL. Similar to BDSN sites, these stations are capable of on-site recording and local storage of all data for more than one day and have batteries to provide backup power. Signals from these stations are digitized at a variety of data rates up to 500 Hz at 24-bit resolution (Table 5.3). In contrast to the BDSN implementation, the NHFN data loggers employ casual FIR filters at high data rates and acausal FIR filters at lower data rates. Because of limitations in telemetry bandwidth and disk storage, 8 of these sites transmit triggered data at 500 sps, using the Murdock, Hutt, and Halbert (MHH) event detection algorithm (Murdock and Hutt, 1983), and continuous data at reduced rates (100, 20 and 1 sps) to the BSL, while the four MPBO sites transmit continuous data at 100 sps (one MPBO site does not have telemetry yet).

The remaining 12 sites of the NHFN have in the past recorded data using RefTek data loggers. These sites do not have continuous telemetry for acquisition and required visits from BSL staff for data recovery. Collection of data from these sites has been discontinued, but efforts are underway to upgrade them with Quanterra Q4120 data loggers and continuous telemetry.

Signals from the 5 SHFN stations are digitized by Nanometrics data loggers at 100 sps and transmit continuous data to Menlo Park by radio. These digital data streams are processed by the Earthworm system with the NCSN data and waveforms are saved when the Earthworm detects an event.

Table 5.1: Stations of the Hayward Fault Network. Each HFN 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. The elevation of the well head (in meters) is relative to the WGS84 reference ellipsoid. The overburden is given in meters. The start dates indicate either the upgrade or installation time. The abbreviations are: BB - Bay Bridge; BR - Briones Reserve; CMS - Cal Memorial Stadium; CB - Carquinez Bridge; DB - Dumbarton Bridge; MPBO - mini-Plate Boundary Observatory RFS - Richmond Field Station; RSRB - Richmond-San Rafael Bridge; SF - San Francisco; SMB - San Mateo Bridge; SMC - St. Mary's College; and, YB - Yerba Buena. The * for stations indicates that the stations are not currently recording data. RSRB is shut down while Caltrans is retrofitting the Richmond-San Rafael bridge (as of April 19, 2001) and YBIB has been off-line since August 24, 2000 when power cables to the site where shut down. Other off-line stations are in the process of being upgraded as funding for equipment becomes available. The table also includes 2 MPBO stations which became operational in the last 2 years, and 3 MPBO borehole sensors that have recently been installed.
Code Net Latitude Longitude Elev (m) Over (m) Date Location
CRQB BK 38.05578 -122.22487 -25.0 38.4 1996/07 - current CB
HERB BK 38.01250 -122.26222 -25.0 217.9 2000/05 - current Hercules
BRIB BK 37.91886 -122.15179 219.7 108.8 1995/07 - current BR, Orinda
RFSB BK 37.91608 -122.33610 -27.3 91.4 1996/01 - current RFS, Richmond
CMSB BK 37.87195 -122.25168 94.7 167.6 1994/12 - current CMS, Berkeley
SMCB BK 37.83881 -122.11159 180.9 3.4 1997/12 - current SMC, Moraga
SVIN BK 38.03325 -122.52638   158.7 2003/08 - current MPBO, St. Vincent's school
OHLN BK 38.00742 -122.27371   196.7 2001/07 - current MPBO, Ohlone Park
MDHL BK 37.84227 -122.49374   160.6 in progress MPBO, Marin Headlands
SBRN BK 37.68562 -122.41127   157.5 2001/08 - current MPBO, San Bruno Mtn.
OXMT BK 37.498 -122.425   194.2 2003/12 - current MPBO, Ox Mtn.
BBEB BK 37.82167 -122.32867   150.0 2002/05 - current BB, Pier E23
E17B BK 37.82086 -122.33534   160.0 1995/08 - current * BB, Pier E17
E07B BK 37.81847 -122.34688   134.0 1996/02 - current * BB, Pier E7
YBIB BK 37.81420 -122.35923 -27.0 61.0 1997/12 - current * BB, Pier E2
YBAB BK 37.80940 -122.36450   3.0 1998/06 - current * BB, YB Anchorage
W05B BK 37.80100 -122.37370   36.3 1997/10 - current * BB, Pier W5
W02B BK 37.79120 -122.38525   57.6 2003/06 - current BB, Pier W2
SFAB BK 37.78610 -122.3893   0.0 1998/06 - current * BB, SF Anchorage
RSRB BK 37.93575 -122.44648 -48.0 109.0 1997/06 - current * RSRB, Pier 34
RB2B BK 37.93 -122.41   133.8 2003/07 - current * RSRB, Pier 58
SM1B BK 37.59403 -122.23242   298.0 not recorded SMB, Pier 343
DB3B BK 37.51295 -122.10857   1.5 1994/09 - 1994/11 DB, Pier 44
          62.5 1994/09 - 1994/09  
          157.9 1994/07 - current *  
DB2B BK 37.50687 -122.11566     1994/07 - current * DB, Pier 27
          189.2 1992/07 - 1992/11  
DB1B BK 37.49947 -122.12755   0.0 1994/07 - 1994/09 DB, Pier 1
          1.5 1994/09 - 1994/09  
          71.6 1994/09 - 1994/09  
          228.0 1993/08 - current *  
CCH1 NC 37.7432 -122.0967 226   1995/05 - current Chabot
CGP1 NC 37.6454 -122.0114 340   1995/03 - current Garin Park
CSU1 NC 37.6430 -121.9402 499   1995/10 - current Sunol
CYD1 NC 37.5629 -122.0967 -23   2002/09 - current Coyote
CMW1 NC 37.5403 -121.8876 343   1995/06 - current Mill Creek

Table 5.2: Instrumentation of the HFN as of 06/30/2005. Every HFN downhole package consists of co-located geophones and accelerometers, with the exception of MPBO sites. 6 HFN sites also have dilatometers (Dilat.) and the 5 MPBO sites have tensor strainmeters (Tensor.) 12 NHFN sites have Quanterra data loggers with continuous telemetry to the BSL. The remaining sites are being upgraded to Quanterra data loggers. The 5 SHFN sites have Nanometrics data loggers with radio telemetry to the USGS. The orientation of the sensors (vertical - Z, horizontals - H1 and H2) are indicated where known or identified as "to be determined" (TBD). The azimuths of the horizontal component geophones have a 180 degree ambiguity owing to the dead vertical component geophone.
Site Geophone Accelerometer Z H1 h2 Data logger Notes Telem.
CRQB Oyo HS-1 Wilcoxon 731A -90 251 341 Q4120   FR
HERB Oyo HS-1 Wilcoxon 731A -90 TBD TBD Q4120   FR
BRIB Oyo HS-1 Wilcoxon 731A -90 79 349 Q4120 Acc. failed, Dilat. FR
RFSB Oyo HS-1 Wilcoxon 731A -90 256 346 Q4120   FR
CMSB Oyo HS-1 Wilcoxon 731A -90 19 109 Q4120   FR
SMCB Oyo HS-1 Wilcoxon 731A -90 76 166 Q4120 Posthole FR
SVIN Mark L-22   -90 298 28 Q4120 Tensor. FR/Rad.
OHLN Mark L-22   -90 313* 43* Q4120 Tensor. FR
MDHL Mark L-22   -90 TBD TBD None at present Tensor.  
SBRN Mark L-22   -90 347 77 Q4120 Tensor. FR
OXMT Mark L-22   -90 163 253 Q4120 Tensor. FR
BBEB Oyo HS-1 Wilcoxon 731A -90 TBD TBD Q4120 Acc. failed Radio
E17B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present    
E07B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present    
YBIB Oyo HS-1 Wilcoxon 731A -90 257 347 None at present Z geop. failed FR/Rad.
YBAB Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present    
W05B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present    
W02B Oyo HS-1 Wilcoxon 731A -90 TBD TBD Q4120   Radio
SFAB None LLNL S-6000 TBD TBD TBD None at present Posthole  
RSRB Oyo HS-1 Wilcoxon 731A -90 50 140 None at present 2 acc. failed FR
RB2B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present 1 acc. failed  
SM1B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present    
DB3B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present Acc. failed  
DB2B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present    
DB1B Oyo HS-1 Wilcoxon 731A -90 TBD TBD None at present Acc. failed  
CCH1 Oyo HS-1 Wilcoxon 731A -90 TBD TBD Nanometrics HRD24 Dilat. Radio
CGP1 Oyo HS-1 Wilcoxon 731A -90 TBD TBD Nanometrics HRD24 Dilat. Radio
CSU1 Oyo HS-1 Wilcoxon 731A -90 TBD TBD Nanometrics HRD24 Dilat. Radio
CYD1 Oyo HS-1 Wilcoxon 731A -90 TBD TBD Nanometrics HRD24 Dilat. Radio
CMW1 Oyo HS-1 Wilcoxon 731A -90 TBD TBD Nanometrics HRD24 Dilat. Radio

Experience has shown that the MHH detector does not provide uniform triggering across the NHFN on the smallest events of interest. In order to insure the recovery of 500 sps data for these earthquakes, a central-site controller has recently been implemented at the BSL using the 500 sps vertical component geophone data for event detection. Originally the 100 sps vertical component geophone data was used for event detection but the bandwidth proved to be inadequate for detection of the smaller events where most of the seismic wave energy was at frequencies above 40 Hz. Triggers from this controller are being used to recover the 500 sps data from the NHFN data loggers.

Data from the NHFN and SHFN are archived at the NCEDC. At this time, the tools are not in place to archive the Hayward fault data together. The NHFN data are archived with the BDSN data, while the SHFN are archived with the NCSN data (Chapter 11). However, the new central-site controller will provide the capability to both include SHFN data in the event detection and extract SHFN waveforms for these events in the future.

As originally planned, the Hayward Fault Network was to consist of 24 to 30 stations, 12-15 each north and south of San Leandro, managed respectively by UCB and USGS. This is not happening quickly, although west of the fault, Caltrans has provided sites along the Bay bridges. This important contribution to the Hayward Fault Network has doubled the number of sites with instrumentation. At times, Caltrans provides holes of opportunity away from the bridges (e.g., HERB), so we have plans for additional stations that will bring the network geometry to a more effective state for imaging and real-time monitoring of the fault.

As a check on the calibration and an example of the capabilities of a borehole installed network, we compare the bandpass filtered (0.3-5 Hz) ground velocity data recorded at NHFN and MPBO stations for a M 7.8 intermediate focus teleseism that occurred in Chile at a depth of 116 km in Figure 5.2.

Figure 5.2: Plot of the P-wave waveforms, recorded by the NHFN/MPBO borehole stations, for a major intermediate focus Chilean earthquake (2005/06/13; 22:44 UT; 116 km deep; $M_{w}$ 7.8; 8460 km S51E of Berkeley). The waveform data were deconvolved to ground velocity, 0.3-5.0 Hz band pass filtered to enhance the P-wave signal and normalized prior to plotting. For comparison, the traces are plotted in order of distance. The waveforms are highly similar at all stations except W02B where there the trace is inverted.
\epsfig{file=nhfn_teles_20050613.eps, width=8cm}\end{center}\end{figure}

Table 5.3: Typical data streams acquired at each NHFN site, with channel name, sampling rate, sampling mode and FIR filter type. C indicates continuous; T triggered; Ca causal; and Ac acausal. The 100 sps channels (EP & HL) are only archived when the 500 sps channels are not available.
Sensor Channel Rate (sps) Mode FIR
Accelerometer CL? 500.0 T Ca
Accelerometer HL? 100.0 C Ca
Accelerometer BL? 20.0 C Ac
Accelerometer LL? 1.0 C Ac
Geophone DP? 500.0 T Ca
Geophone EP? 100.0 C Ca
Geophone BP? 20.0 C Ac
Geophone LP? 1.0 C Ac

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