| 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 |
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] |
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