Data Network Summary Table

Network Purpose Number of Sites Sensitivity Measurement Interval References
NCSN Seismicity High-grain, short-period vertical component Northern California Seismic Network seismometers collect data within 25 km of Parkfield. Earthquake magnitudes and locations can be estimated within 3 - 5 minutes of occurrence. 40 M greater than or equal to 1.0 continuous Nishioka and Michael [1987]
Continuous dilational strain (dilatometers) These instruments measure volumetric strain changes in the Earth near active faults. Dilatometers measure changes in volume strain near the fault. 7 10-9* 10 minutes Myren and Johnston [1989]
Continuous tensor strain These instruments measure strain changes on 3 components in the Earth near active faults. Over short time periods they can detect changes of 10 parts-per-billion (1 inch in 1600 miles). Tensor strainmeters measure horizontal strain in three nonparallel directions. 3 10-9*

15 minutes

30 minutes (EDT,FLT)

18 minutes
(DLT)

Gladwin et al. [1987]
Magnetic Field These instruments measure local changes in the earth's magnetic field near active faults. Over short time periods they can detect changes of as small as 1/50,000th of the earth's magnetic field. 7 0.25 nT 10 minutes Teague et al. [1994]
Creepmeter Creepmeters continuously monitor fault movement within a few meters of fault zones to characterize the rate and nature of fault slip. They can detect changes of about 0.1 millimeters. 12 0.05 mm* 10 minutes Schulz [1989]
Ground water level Fluid pressure transducers in well boreholes measure changes in the height of the ground water table associated with each well-aquifer system. Over short time periods they can detect water level changes of a few millimeters. 10 1 mm 15 minutes Roeloffs et al. [1989]
Two-color EDM A two-color Electronic Distance Meter (EDM) measures the changes in distances on several baselines near Parkfield at a precision of about 0.5 mm. These changes reflect fault slip on the San Andreas and strain accumulation 18 lines 1 mm 3 / week Langbein et al.[1990]
Portable EDM Data from this network provide a measure of surface and shallow slip near Middle Mountain. 20 lines 1 mm 1 / year Bakun [1987]
Tilt (discontinued) 5 1 micro rad 10 minutes Johnston [1978]
Groundwater radon (discontinued) 2 1 pCi/L 10 minutes Noguichi and Wakita [1977]
Soil Hydrogen (discontinued) 7 10 ppm 10 minutes Sato et al. [1986]
Resistivity 6 dipoles 1% daily average Park [1991]
Ultra-low frequency magnetic field 2 1 pT 30 minute average McGill et al. [1993]
E-M Field 3 magnetic, 2 electric Morrison
Continuous GPS GPS ( Positioning System) measures displacements at several points near Parkfield with a precision of 2 to 3 mm in the horizontal and about 10 mm in the vertical. 6 2 mm 1-day average Langbein oral comm. [2001)
Campaign GPS 34 3 mm 1 every 3 years

Langbein oral comm. [2001)

King et al. [1987]

Leveling 7 lines 1 mm/km infrequent Sylvester [1991]
HRSN Borehole Seismic Network These instruments measure strain changes on 3 components in the Earth near active faults. Over short time periods they can detect changes of 10 parts-per-billion (1 inch in 1600 miles) 10 M greater than or equal to -1 continuous Michelini et al. [1991]
Vibrosis waveform (discontinued) Surface vibrator used by UCB is a source of seismic energy for an investigation of subtle changes. 80 paths 5 ms 4 / year  
UPSAR Dense Seismic Array 14 geophone, 14 accelerometers in 1 km2 area M greater than or equal to 3 continuous Fletcher et al. [1992]
EPRI Dense Seismic Array (discontinued) Force balance accelerometers (FBA) adequitly record magnitude 3 and 4 shocks. 21 FBA in 120 m radius continuous Schneider et al. [1990]
Liquefaction Array (discontinued) 5 accelerometers, 7 piezometers Holzer et al. [1988]
CDMG Strong motion array 48 3-componenet, SMA M greater than or equal to 4 triggered McJunkin and Shakal [1983]
GEOS digital recording (acceleration, velocity and volume strain) Force balance accelerometers (FBA) adequilty record magnitude 3 and 4 shocks. 13 3-component, FBA triggered Borcherdt et al. [1985]
Rupture Video camera 2 cameras M greater than or equal to 4 triggered
Turkey Flat Strong motion array 6 3-component FBA, 2 downhole, 2 km linear array triggered Real and Tucker [1988]
Cramer
[1995]