Parkfield Area Crustal Deformation Measurements

Parkfield has been the site of moderate earthquakes (Magnitude 6) about every 20 years. Based on the historic record and other evidence, the U.S. Geological Survey had predicted that a "Parkfield" earthquake would occur before the end of 1993. On September 28, 2004 a Magnitude 6.0 earthquake, epicenter 11 kilometers southeast of the town of Parkfield, occurred at 17:15:14 UTC. The Parkfield area continues to be monitored to study the complete earthquake cycle using many instruments to document the deformation prior, during, and after this earthquake. These observations will guide both theoretical and laboratory studies on the causes of earthquakes.

Plots of Current Data

For most instruments, measurements are made and sent to computers several times each hour. To see these data, choose among the following:

DISCLAIMER: The plots and data on this site are generated automatically and are not reviewed. They should not be used for engineering, legal, or any other critical applications.

Data for the Last 7 Days

• Plot Creep Measurements
• Plot Dilatational Strain Measurements
• Plot GTSM Tensor Strain Measurements
• Plot Environmental Data

Data for the Last 30 Days

• Plot Creep Measurements
• Plot Dilatational Strain Measurements
• Plot GTSM Tensor Strain Measurements

Long-Term Data

• Plot Creep Measurements
• Plot Dilatational Strain Measurements
• Plot GTSM Tensor Strain Measurements

 

Quick View of Data for all Regions

Complete List of Instruments for Parkfield

 

Instruments Located in The Parkfield Area

Map of Instrument Locations

• Creepmeters

Creepmeters continuously monitor near-surface fault movement on the actual fault traces to characterize the rate and nature of fault slip. They can detect changes of about 0.1 millimeters.

 

• Dilational Strainmeters

These instruments measure the volumetric stretching and squeezing of the ground near active faults. Over short time periods they can detect changes of 1-part-per-billion (1 inch in 16,000 miles).

 

• Tensor Strainmeters

These instruments measure the directional stretching and squeezing in the ground near active faults. Over short time periods they can detect changes of 1-part-per-billion (1 inch in 16,000 miles).

 

• Tiltmeters

Tiltmeters continuously monitor rotation or tilting in the ground near active faults by precisely measuring either the movement of a pendulum or fluid levels in connected reservoirs (rather like the ring in a bathtub) as the ground tilts. Measurements can easily be made to better than 1 part per billion.

 

• Geodesy

The location of many land survey markers located in active fault zones in the United States are measured using Global Positioning System (GPS) receivers. These receivers are a high precision version of the small handheld receivers available today in electronics stores.The high precision version together with appropriate computer processing is capable of measuring the horizontal position of sites with an accuracy of a few millimeters (mm), and the vertical position with an accuracy of about 10 mm. Using GPS, relative motion of sites a few hundred kilometers apart can be determined to a precision of 1 part per 10 million, and relative motion of sites on opposite ends of the continent to a precision of 1 part per billion. The U.S. Naval Observatory maintains a site containing general information on the GPS system.

 

• Two Color EDM

The two-color EDM (Electronic Distance Meter) is an ultra-precise distance measuring instrument with a precision of 0.5 to 1.0 mm for ranges between 1 and 12 km. This instrument is used to measure crustal deformation along faults and near volcanoes. Currently, we use this instrument to monitor the deformation of the Long Valley Caldera east of Yosemite, and at Parkfield, California along the San Andreas fault. To take advantage of the instrument's high precision, these measurements are made frequently, typically several times each week. In addition, we make infrequent measurements of distances at other sites in California to measure strain accumulation within the San Andreas fault zone. The USGS also maintains a website displaying Parkfield Area two color EDM data.