Subsections


Northern Hayward Fault Network



Introduction

Complementary to the regional surface broadband and short-period networks, the Hayward Fault Network (HFN) (Figure 3.10 and Table 3.5) is a deployment of borehole-installed, wide-dynamic range seismographic stations along the Hayward Fault and throughout the San Francisco Bay toll bridges system. Development of the HFN initiated through a cooperative effort between the BSL (Berkeley Seismological Laboratory) and the USGS, with support from the USGS, Caltrans, EPRI, the University of California Campus/Laboratory Collaboration (CLC) program, LLNL, and LBNL. The project's objectives included an initial characterization period followed by longer-term monitoring effort using a backbone of stations from among the initial characterization set. Subsequent funding from Caltrans, however, has allowed for continued expansion of the backbone station set for additional coverage in critical locations.

The HFN consists of two components. The Northern Hayward Fault Network (NHFN), operated by the BSL, consists of 30 stations in various developmental and operational stages. These include stations located on Bay Area bridges, at free-field locations, and now at sites of the Mini-PBO (MPBO) project (installed with support from NSF and the member institutions of the MPBO project). The NHFN is considered part of the BDSN and uses the network code BK. The Southern Hayward Fault Network (SHFN) is operated by the USGS and currently consists of 5 stations. This network is considered part of the NCSN and uses the network code NC. The purpose of the HFN is fourfold: 1) to contribute operational data to California real-time seismic monitoring for response applications and the collection of basic data for long-term hazards mitigation, 2) to increase substantially the sensitivity of seismic data to low amplitude seismic signals, 3) to increase the recorded bandwidth for seismic events along the Hayward fault, and 4) to obtain bedrock ground motion signals at the bridges from more frequent, smaller earthquakes.

In addition to the NHFN's contribution to real-time seismic monitoring in California, the mix of NHFN sites in near- and far- field sites and the high-sensitivity (high signal-to-noise), high-frequency broadband data recorded by the NHFN also contributes significantly to a variety of scientific objectives including: a) investigating bridge responses to stronger ground motions from real earthquakes; b) obtaining a significantly lower detection threshold for microearthquakes and possible non-volcanic tremor signals; c) increasing the resolution of the fault-zone seismic structure (e.g., in the vicinity of the Rodgers Creek/Hayward Fault step over); d) improving monitoring of spatial and temporal evolution of seismicity (to magnitudes below $M \sim 0.0$) that may signal behavior indicative of the nucleation of large damaging earthquakes; e) investigating earthquake scaling, physics, and related fault processes; f) improving working models for the Hayward fault; and g) using these models to make source-specific response calculations for estimating strong ground shaking throughout the Bay Area.

Below we focus primarily on activities associated with BSL operations of the NHFN component of the HFN.

Figure 3.10: Map showing the locations of the HFN stations operated by the BSL (NHFN - squares and diamonds) and the USGS (SHFN - circles). Operational sites are filled blue/black, while sites in progress are yellow/grey. Other instrumented but currently non-operational boreholes are indicated as open symbols. Currently, station BBEB operates only as a telemetry repeater site because access to the borehole was cut off during seismic retrofit work on the eastern span of the Bay Bridge.
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\epsfig{file=nhfn09_map.eps, width=15cm}\end{center}\end{figure*}


Table 3.5: 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 CMAB and PINB indicates that the station name has not yet been approved and may change. The * in the Date column indicates the stations that have recorded data from an earlier period (some manually retrieved from tapes), but that are currently off-line. Note that due to Bay Bridge retrofit work, station BBEB now operates only as a telemetry relay station and no longer records seismic activity.
Code Net Latitude Longitude Elev (m) Over (m) Date Location
VALB BK 38.1215 -122.2753 -24 155.8 2005/11 - current Napa River Bridge
PETB BK 38.1189 -122.5011 -30 113 in progress Petaluma River Bridge
CMAB* BK 38.06885 -122.22909 19.2 tbd in progress Cal Maritime Academy
CRQB BK 38.05578 -122.22487 -25 38.4 1996/07 - current CB
HERB BK 38.01250 -122.26222 -25 217.9 2000/05 - current Hercules
PINB* BK 38.0113 -122.3653 tbd tbd in progress Point Pinole
BRIB BK 37.91886 -122.15179 219.7 108.8 1995/06 - 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 - 2007/06 SMC, Moraga
SM2B BK 37.8387 -122.1102 200 150.9 2007/06 - current SMC, Moraga
SVIN BK 38.03325 -122.52638 -21 158.7 2003/08 - current MPBO, St. Vincent's school
OHLN BK 38.00742 -122.27371 -0 196.7 2001/07 - current MPBO, Ohlone Park
MHDL BK 37.84227 -122.49374 94 160.6 2006/05 - current MPBO, Marin Headlands
SBRN BK 37.68562 -122.41127 4 157.5 2001/08 - current MPBO, San Bruno Mtn.
OXMT BK 37.4994 -122.4243 209 194.2 2003/12 - current MPBO, Ox Mtn.
BBEB BK 37.82167 -122.32867 -31 150.0 2002/05 - 2007/08 * BB, Pier E23
E17B BK 37.82086 -122.33534   160.0 1995/08 - current * BB, Pier E17
E07B BK 37.81847 -122.34688 tbd 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 tbd 36.3 1997/10 - current * BB, Pier W5
W02B BK 37.79120 -122.38525 -45 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 tbd 133.8 in progress 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 3.6: Instrumentation of the HFN as of 06/30/2008. Every HFN downhole package consists of collocated 3-component geophones and accelerometers, with the exception of MPBO sites which have only 3-component geophones and are also collecting tensor strainmeter data. Six HFN sites (5 of the SHFN and 1 of the NHFN) also have dilatometers (Dilat.). Currently, 13 NHFN sites have Quanterra data loggers with continuous telemetry to the BSL. The remaining backbone sites are either still being developed with support from Caltrans or 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).
Site Geophone Accelerometer Z H1 h2 data logger Notes Telem.
VALB Oyo HS-1 Wilcoxon 731A TBD TBD TBD Q330   FR
PETB Oyo HS-1 Wilcoxon 731A TBD TBD TBD TBD   TBD
CMAB Oyo HS-1 Wilcoxon 731A TBD TBD TBD TBD   TBD
CRQB Oyo HS-1 Wilcoxon 731A -90 251 341 Q4120   FR
HERB Oyo HS-1 Wilcoxon 731A -90 TBD TBD Q4120   FR
PINB Oyo HS-1 Wilcoxon 731A TBD TBD TBD TBD   TBD
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 None at present Posthole FR
SM2B Oyo HS-1 Wilcoxon 731A TBD TBD TBD Q4120   FR
SVIN Mark L-22   -90 298 28 Q4120 Tensor. FR/Rad.
OHLN Mark L-22   -90 313 43 Q4120 Tensor. FR
MHDL Mark L-22   -90 TBD TBD Q4120 Tensor. FR
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 None at present 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


NHFN Overview

The initial characterization period of HFN development ended in 1997. During that period, the NHFN sensors provided signals to on-site, stand-alone Quanterra Q730 and RefTek 72A-07 data loggers, and manual retrieval and download of data tapes was required. Also in that year, the long-term monitoring phase of the project began, involving the installation of 24-bit data acquisition and communication platforms and data telemetry to the BSL archives for a backbone of the initial NHFN stations.

Over the years, Caltrans has provided additional support for the upgrade of two non-backbone sites to backbone operational status and for the addition of several new sites to the monitoring backbone. These expansion efforts are ongoing. Also since February 1 of 2007, the 5 stations of the MPBO project have been folded into the NHFN.

Of the 30 stations considered part of the NHFN history, 13 of the stations are currently operational, with telemetered data streams flowing continuously into the BSL's BDSN processing stream with subsequent archival in the Northern California Earthquake Data Center (NCEDC) archive. These include the 5 MPBO sites. Nine of the 30 stations are non-backbone stations that have not been upgraded to continuous telemetry. Though collection of data from these sites has been discontinued, their borehole sensor packages are still in place (having been grouted in), and efforts to find funding for upgrade of these sites with Quanterra Q4120, Q730, or Q330 data loggers and continuous telemetry continue. Two previously active backbone sites (BBEB and SMCB) have been taken out of service permanently. BBEB was taken out of service when its sensor cable was severed by contractors during seismic retrofit work on the east span of the Bay Bridge in August of 2007. The site now operates only as a telemetry repeater site. SMCB (a shallow post-hole site) was taken out of service after it was upgraded to a deep borehole installation in 2007. The upgraded deep borehole site (one of the 30 NHFN stations listed) is now named SM2B.

The remaining 6 sites (PETB, RB2B, E07B, W05B, CMAB, and PINB) are in the process of being added to the NHFN backbone. Four of the sites have been drilled and instrumented and are awaiting installation of their infrastructures, electronics, and telemetry (PETB, RB2B, E07B, and W05B). As of the writing of this report, drilling (provided by Caltrans) has begun on an additional site (CMAB) located at the Cal Maritime Academy. This site is intended to replace a particularly noisy backbone station at the south end of the Carquinez bridge (CRQB). With support for drilling and the purchase of a sensor package from Caltrans, the plan is to transfer the surface infrastructure and recording equipment at CRQB to the Cal Maritime site once drilling has been completed.

After complex negotiations involving (among others) the East Bay Regional Parks District and UNAVCO, permission was given to create an additional site (PINB) at Pt. Pinole Regional Park. However, it has now been recognized that installation of a deep borehole at this site is potentially not feasible due to environmental issues (in the past, the park had been a dynamite manufacturing facility, leaving the possibility that liberation of chemical contaminants may occur from extraction of borehole materials during drilling). We are currently in the process of evaluating the situation further to decide whether or not the PINB installation will need to be abandoned in favor of an alternative future site.


Table 3.7: Typical data streams acquired at NHFN sites, with channel name, sampling rate, sampling mode, and FIR filter type. C indicates continuous, T triggered, Ca causal, and Ac acausal. Typically, the DP1 continuous channel is archived and the remaining high sample rate data (i.e., CL and DP channels) are archived as triggered snippets. Prior to September 2004, however, only triggered data was archived for all high sample rate channels. Currently operational stations CRQB, HERB, BRIB, RFSB, CMSB, SM2B, and W02B record at maximum sample rates of 500 Hz; VALB at maximum 200 Hz and MPBO sites (SVIN, OHLN, MHDL, SBRN, OXMT) at maximum 100 Hz.
Sensor Channel Rate (sps) Mode FIR
Accelerometer CL? 500.0 T Ca
Accelerometer HL? 200.0 C Ca
Accelerometer BL? 20.0 C Ac
Accelerometer LL? 1.0 C Ac
Geophone DP? 500.0 T,C Ca
Geophone EP? 200.0 C Ca
Geophone EP? 100.0 C Ca
Geophone BP? 20.0 C Ac
Geophone LP? 1.0 C Ac


Installation/Instrumentation: The NHFN Sensor packages are generally installed at depths ranging between 100 and 200 m, the non-backbone, non-operational Dumbarton bridge sites being exceptions with sensors at multiple depths (Table 3.5).

The five former MPBO sites that are now part of the NHFN have 3-component borehole geophone packages. Velocity measurements for the MPBO sites are provided by Mark Products L-22 2 Hz geophones (Table 3.6). All the remaining backbone and non-backbone NHFN sites have six-component borehole sensor packages. The six-component packages were designed and fabricated at LBNL's Geophysical Measurement Facility and have three channels of acceleration, provided by Wilcoxon 731A piezoelectric accelerometers, and three channels of velocity, provided by Oyo HS-1 4.5 Hz geophones.

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.

All 13 operational NHFN backbone sites have Quanterra data loggers with continuous telemetry to the BSL. Signals from these stations are digitized at a variety of data rates up to 500 Hz at 24-bit resolution (Table 3.7). The data loggers employ causal FIR filters at high data rates and acausal FIR filters at lower data rates.

Data Rates and Channels: Because of limitations in telemetry bandwidth and disk storage, 7 of the 8 (excluding VALB) six-component NHFN stations transmit maximum 500 Hz data, one channel of geophone data continuously (i.e., their vertical geophone channels), and an additional 3 channels of triggered data in 90 sec. snippets. A Murdock, Hutt, and Halbert (MHH) event detection algorithm (Murdock and Hutt, 1983) is operated independently at each station on 500 sps data for trigger determinations. Because the accelerometer data is generally quieter, the 3 triggered channels are taken from the Wilcoxon accelerometers when possible. However, there is a tendency for these powered sensors to fail, and, in such cases, geophone channels are substituted for the failed accelerometers. Station VALB also transmits data from only 4 channels; however, all channels are transmitted continuously at a maximum of 200 Hz sampling. Continuous data for all channels at reduced rates (20 and 1 sps) are also transmitted to and archived at the BSL. The five MPBO originated sites transmit their 3-component continuous geophone data streams, which are also archived at BSL, at 100, 20, and 1 sps.

Integration with the NCSS, SeisNetWatch, and SeismiQuery: The NHFN is primarily a research network that complements regional surface networks by providing downhole recordings of very low amplitude seismic signals (e.g., from micro-earthquakes or non-volcanic tremor) at high gain and low noise. Nonetheless, we have now also completed the integration of data flow from all operating NHFN stations into the Northern California Seismic System (NCSS) real-time/automated processing stream for response applications and collection of basic data for long-term hazards mitigation. The NCSS is a joint USGS (Menlo Park) and Berkeley Seismological Laboratory (BSL) entity with earthquake reporting responsibility for Northern California, and data from networks operated by both institutions are processed jointly to fulfill this responsibility.

Through this integration, the NHFN picks, waveforms, and NCSS event locations and magnitudes are automatically entered into a database where they are immediately available to the public through the NCEDC and its DART (Data Available in Real Time) buffer. The capability for monitoring state of health information for all NHFN stations using SeisNetWatch has also now been added, and up-to-date dataless SEED formatted metadata is now made available by the NCEDC with the SeismiQuery software tool.

Figure 3.11: Plot showing typically observed background noise PSD for the NHFN borehole stations (including the MPBO in dashed lines) as a function of frequency. The data are for a 50 sec period on August 24, 2009 beginning at 02:21:40 (AM) local time on a Monday morning. Note that there is considerable variation in the general level and structure of the individual station background noise PSD estimates. The signals from three of the stations (RFSB, SM2B, and VALB) have 60 Hz noise (sometimes accompanied by 120 and 180 Hz harmonics), which is indicative of the presence of ground loops that need to be addressed. The PSD ranking (lowest to highest) of the stations at 3 Hz (near minimum PSD for most NHFN stations) is:
OXMT.BK.EP1 -122.49
SVIN.BK.EP1 -120.97
CMSB.BK.DP1 -120.94
OHLN.BK.EP1 -120.46
SBRN.BK.EP1 -115.60
BRIB.BK.DP1 -114.34
MHDL.BK.EP1 -113.98
SM2B.BK.DP1 -113.35
HERB.BK.DP1 -93.31
VALB.BK.EP1 -92.63
RFSB.BK.DP1 -85.24
CRQB.BK.DP1 -75.93
W02B.BK.DP1 -57.26
\begin{figure}\centering\setlength{\belowcaptionskip}{3pt}\epsfig{file=nhfn09_PSD.eps, width=7cm}\end{figure}

Figure 3.12: Plot of unfiltered P-wave seismograms, recorded on the geophones of the 13 NHFN borehole stations operational at the time of a recent Bay Area earthquake (13 September 2009, M3.2 Brentwood, CA). This event was exceptionally deep (14.1 km depth) and occurred $\sim$ 40 km east of the center of the NHFN. Despite its distance and small magnitude, the event was well recorded by several of the NHFN stations. However, it is also clear from the varied responses of the stations that some stations are either much more sensitive or more noisy than others. In addition, some stations were entirely unresponsive to seismic signals from this event. Both conditions indicate that the NHFN was under-performing during this event, and corrective actions are being taken.
\begin{figure}\centering\setlength{\abovecaptionskip}{0pt}\setlength{\belowcaptionskip}{0pt}\epsfig{file=nhfn09_lcl.eps, width=7cm}\end{figure}

Figure 3.13: Plot of P-wave seismograms of the teleseismic $M_{w}$ 7.6 earthquake in the Tonga region (Lat.: 23.050S; Lon.: 174.668W; depth 34 km) occurring on March 19, 2009 18:17:40 (UTC) recorded on the DP1 (vertical) channels of the 13 NHFN borehole stations in operation at the time. Here, vertical component geophone (velocity) data have been 0.1-0.5 Hz bandpass filtered, and the highest available sampling rate for a given component is plotted. In this case, corrections for differences in instrument responses (e.g., between geophones and accelerometers) were not made.
\begin{figure}\centering\setlength{\belowcaptionskip}{3pt}\epsfig{file=nhfn09_teles.eps, width=7.5cm}\end{figure}

Station Maintenance

Ongoing network maintenance involves regular inspection of the collected seismic waveform data and spectra of nearby seismic events, and also of noise samples. Other common problems include changes to background noise levels due to ground loops and failing preamps, as well as power and telemetry issues. Troubleshooting and remediation of problems often benefit from a coordinated effort, with a technician at the BSL examining seismic waveforms and spectra while the field technicians are still on site. BSL technicians and researchers regularly review data and assist in troubleshooting.

The NHFN station hardware has proven to be relatively reliable. Nonetheless, numerous maintenance and performance enhancement measures are still carried out. In particular, when a new station is added to the backbone, extensive testing and correction for sources of instrumental noise (e.g., grounding related issues) and telemetry through-put are carried out to optimize the sensitivity of the station. Examples of maintenance and enhancement measures that are typically performed include: 1) testing of radio links to ascertain reasons for unusually large numbers of dropped packets, 2) troubleshooting sporadic problems with numerous frame relay telemetry dropouts, 3) manual power recycle and testing of hung Quanterra data loggers, 4) replacement of blown fuses or other problems relating to dead channels identified through remote monitoring at the BSL, 5) repair of frame relay and power supply problems when they arise, and 6) correcting problems that arise due to various causes, such as weather or cultural activity.

As an example, this year maintenance visits were necessary at several of the MPBO stations. At OHLN, BSL and USGS instruments are collocated. Power is provided by the local school district. Several times during the past year, power to the seismic site failed mysteriously and was restored after BSL personnel contacted the school. In May of 2009, BSL engineers contacted the school district to replace the AC circuit breaker. Since it was replaced, power has not failed again. All of the back up batteries that were originally installed in 2001 were also replaced. At the station SBRN, all of the batteries were replaced, and additional batteries were installed to increase the reserve capacity. At SVIN, the internal disk drive of the data logger failed and was replaced.

Quality Control

2008-2009 Activities

Over the past year, in addition to routine maintenance, operations, quality control, and data collection, NHFN project activities have included: b) efforts to obtain additional funds for future upgrade and expansion of the network, c) leveraging NHFN activities through partnerships with various institutions outside of BSL, d) network adaptations to compensate for changing conditions associated with retrofit work on Bay Area bridges, and e) new station additions and network expansion efforts.

Additional Funding

Operation of this Bay Area borehole network is funded by the ANSS and through a partnership with the California Department of Transportation (Caltrans). ANSS provides operations and maintenance (O&M) support for a fixed subset of 9 operational stations that were initiated as part of previous projects in which the USGS was a participant. Caltrans provides developmental and O&M support for an additional 10 stations that have been or are in the process of being added to the network with Caltrans partnership grants. Caltrans also continues to provide additional support for upgrade and expansion when possible.

Currently, we are also in the process of preparing a competitive proposal to Caltrans to continue to expand the NHFN with additional borehole installations and to upgrade several NHFN sites with strong-motion surface sensors to provide up-hole down-hole data for fundamental research on amplification effects in the upper $\sim$1-200 meters.

Partnerships

The NHFN is heavily leveraged through partnerships with various institutions, and we have continued to nurture and expand these relationships. Over the past year we have continued our collaborative partnerships with Caltrans, St. Mary's College, the Cal Maritime Academy, the East Bay Parks District, UNAVCO, Lawrence Berkeley National Laboratory, and non-ANSS components of the USGS (e.g., regarding potential installation at the WildCat site).

New Installations

Since reorganization of engineering support for the NHFN project this past year significant progress on the development has been made at 2 sites (PETB and RB2B) that we expect to have operational within a few months. At these sites deep boreholes have been drilled and instrumented, and infrastructure, power, and telemetry are in the final stages of being completed. Testing and noise reduction efforts will follow completion. Two additional sites have been instrumented and are awaiting completion of the retrofit of the Bay Bridge before being completed and brought on-line (E07B and W05B).

As of the writing of this report, permission and citing has been completed and drilling (provided by Caltrans) has begun on an additional site (CMAB) located at the Cal Maritime Academy. This site is intended to replace a particularly noisy backbone station at the south end of the Carquinez bridge (CRQB). With support for drilling and the purchase of a sensor package from Caltrans, the plan is to transfer the surface infrastructure and recording equipment at CRQB to the Cal Maritime site once drilling has been completed.

This year, complex negotiations involving (among others) the East Bay Regional Parks District and UNAVCO were finally completed, giving us permission to create borehole site (PINB) at Pt. Pinole Regional Park. However, it has now been recognized that installation of a deep borehole at this site is potentially problematic due to environmental issues (in the past, the park had been a dynamite manufacturing facility, leaving the possibility that liberation of chemical contaminants may occur from extraction of borehole materials during drilling). We are currently in the process of evaluating the situation further to decide whether or not the PINB installation will need to be abandoned in favor of an alternative future site (possibly at the Wildcat location).

Acknowledgments

Thomas V. McEvilly, who passed away in February 2002, was instrumental in developing the Hayward Fault Network, and, without his dedication and hard work, the creation and continued operation of the NHFN would not have been possible.

Under Bob Nadeau's and Doug Dreger's general supervision, Rich Clymer, Doug Neuhauser, Bob Uhrhammer, Bill Karavas, John Friday, Taka'aki Taira, and Rick Lellinger all contribute to the operation of the NHFN. Bob Nadeau prepared this section with help from Taka'aki Taira and Bob Uhrhammer.

Support for the NHFN is provided by the USGS through the NEHRP grant program (grant no. 07HQAG0014) and by Caltrans through grant no. 59A0578. Pat Hipley of Caltrans has been instrumental in the effort to continue to upgrade and expand the network. Larry Hutchings and William Foxall of LLNL have also been important collaborators on the project in years past.

References

Rodgers, P.W., A.J. Martin, M.C. Robertson, M.M. Hsu, and D.B. Harris, Signal-Coil Calibration of Electromagnetic Seismometers, Bull. Seism. Soc. Am., 85(3), 845-850, 1995.

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

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