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The map shows the locations of creepmeters in the Parkfield area that are used to measure fault slip.

Description of a creepmeter

A creepmeter measures the displacement between 2 piers or monuments that are located on opposite sides of the fault and span nearly the entire fault zone over a 30 meter length. Typically, an invar wire is anchored to one pier and is stretched across the fault. Its displacement relative to the second pier is measured precisely electronically and checked periodically with a mechanical measurement. Since the angle of the wire is approximately 30 degrees from the strike of the fault, the change is distance between the two piers is directly proportionaly to fault slip.

Description of fault creep data

Because the piers are anchored to about 2 meters depth, they are subject to the influence of seasonal (winter) rainfall. Many of the creepmeters show an annual cycle due to the wetting and drying of the clayey soil withing the fault zone. In addition, creep is influenced by large rainfall (April 1991) and nearby earthquakes such as the M6.7 earthquake at Coalinga in 1983.

The measurements of fault creep are made once every 10 minutes and are telemetred to our computers in Menlo Park, CA. The plots shown below are the measurements of fault creep for a variety of time periods. The fault slip data for periods of a year or more have been decimated to daily measurements. In addition, measurements prior to January 1995 have been reconciled with field notes and mechanical measurments. The more recent data are the electronic measurements that have been merged with the older data and THESE MORE RECENT DATA SHOULD BE TREATED AS PROVISIONAL MEASUREMENTS.

Creepmeter data

• Plot Measurements since 1966 (updated weekly)
• Plot Measurements since 1966; secular trend removed (updated weekly)
• Plot Measurements from past 10 years (updated weekly)
• Plot Measurements from past 10 years; secular trend removed (updated weekly)
• Plot Measurements from the past year; secular trend removed (updated weekly)
• Plot Measurements from the last 90 days (updated daily)
• Plot Measurements from the last 30 days (updated daily)
• Plot Measurements over past 7 days

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