
Parkfield, The Earthquake Study Capital of the World
The town of Parkfield, located on the San Andreas Fault in central California and 200 miles from San Francisco, is one of the world’s most seismically active areas. It has been the site of an intensive earthquake study since the late 1970's.
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The Parkfield Earthquake Experiment, led by the United States Geological Survey (USGS) and the State of California, is a long-term earthquake research project on the San Andreas Fault. Its goal is to observe the fault and better understand the physics of earthquakes - what actually happens on the fault and in the surrounding region before, during and after an earthquake.
Ultimately, scientists hope to better understand the earthquake process and, if possible, to provide a scientific basis for earthquake prediction.
The Earth's crust is fractured into a series of "plates" that have been moving very slowly over the Earth's surface for millions of years. Two of these moving plates meet in western California and the boundary between them is the San Andreas Fault. The Pacific Plate (on the west) moves northwestward relative to the North American Plate (on the east), causing earthquakes along the fault.
The San Andreas Fault is approximately 1300 km (800 miles) long. If a person stood on one side of the fault and looked across it, the block on the opposite side would appear to have moved to the right. Surveying shows a drift at the rate of as much as 2 inches per year
Sudden offset that initiates a great earthquake occurs on only one section of the fault at a time. Total offset accumulates through time in an uneven fashion, primarily by movement on a first section of the fault and then on another one. Great earthquakes are produced by sections that remain "locked" and quiet over a hundred or more years while strain builds up then, in great lurches, released.
During the 1906 earthquake in the San Francisco region, roads, fences, and rows of trees and bushes that crossed the fault were offset several meters or yards. Earthquakes are the most costly natural hazard faced by the United States.
The town of Parkfield, population 37, was chosen for the experiment for several reasons. Moderate earthquakes (magnitude about 6) have occurred on the Parkfield section of the San Andreas Fault at fairly regular intervals- one approximately every 22 years, except for the last one in 2004. All these Parkfield earthquakes have struck in the same area and historical seismograms show that at least the 1934 and 1966 shocks initiated at the same point on the fault. These observations suggest that there may be some predictability in the occurrence of earthquakes.
Building on more than 15 years of experience from the Parkfield Earthquake Experiment, the National Science Foundation (NSF) and the USGS started in June 2004 to drill a deep hole in order to install instruments directly within the San Andreas Fault Zone near the initiation point of previous magnitude 6. They reached the fault’s active zone, 2 miles deep, early August 2005.
These instruments, set 2 to 3 kms beneath the Earth's surface, will form a San Andreas Fault Observatory at Depth (SAFOD). This project is part of the global EarthScope Project and will directly reveal, for the first time, the physical and chemical processes controlling earthquake generation within a seismically active fault. As Dr Mark Zobak, one of SAFOD’s principal investigators, told the BBC: ”It’s like using a stethoscope and listening very, very carefully”.
Fault-zone rocks and fluids will be retrieved for laboratory analyses, and geophysical measurements will be made within the active fault zone. SAFOD's long-term monitoring activities will include detailed seismological observations of small to moderate earthquakes and continuous measurements of rock deformation and other parameters during the earthquake cycle.
SAFOD will provide direct information on the composition and mechanical properties of rocks in the fault zone, the nature of stresses responsible for earthquakes, the role of fluids in controlling faulting and earthquake recurrence, and the physics of earthquake initiation and rupture. By observing quakes "up close," SAFOD will mark a major advance in the pursuit of a rigorous scientific basis for assessing earthquake hazards and predicting earthquakes.
Sources and Resources: United States Geological Survey (USGS), EarthScope, SAFOD
USGS’s website: http://www.usgs.gov
Safod’s website: http://earthscope.org/safod/
Parkfield Experiment http://quake.wr.usgs.gov/research/parkfield
Ultimately, scientists hope to better understand the earthquake process and, if possible, to provide a scientific basis for earthquake prediction.
The Earth's crust is fractured into a series of "plates" that have been moving very slowly over the Earth's surface for millions of years. Two of these moving plates meet in western California and the boundary between them is the San Andreas Fault. The Pacific Plate (on the west) moves northwestward relative to the North American Plate (on the east), causing earthquakes along the fault.
The San Andreas Fault is approximately 1300 km (800 miles) long. If a person stood on one side of the fault and looked across it, the block on the opposite side would appear to have moved to the right. Surveying shows a drift at the rate of as much as 2 inches per year
Sudden offset that initiates a great earthquake occurs on only one section of the fault at a time. Total offset accumulates through time in an uneven fashion, primarily by movement on a first section of the fault and then on another one. Great earthquakes are produced by sections that remain "locked" and quiet over a hundred or more years while strain builds up then, in great lurches, released.
During the 1906 earthquake in the San Francisco region, roads, fences, and rows of trees and bushes that crossed the fault were offset several meters or yards. Earthquakes are the most costly natural hazard faced by the United States.
The town of Parkfield, population 37, was chosen for the experiment for several reasons. Moderate earthquakes (magnitude about 6) have occurred on the Parkfield section of the San Andreas Fault at fairly regular intervals- one approximately every 22 years, except for the last one in 2004. All these Parkfield earthquakes have struck in the same area and historical seismograms show that at least the 1934 and 1966 shocks initiated at the same point on the fault. These observations suggest that there may be some predictability in the occurrence of earthquakes.
Building on more than 15 years of experience from the Parkfield Earthquake Experiment, the National Science Foundation (NSF) and the USGS started in June 2004 to drill a deep hole in order to install instruments directly within the San Andreas Fault Zone near the initiation point of previous magnitude 6. They reached the fault’s active zone, 2 miles deep, early August 2005.
These instruments, set 2 to 3 kms beneath the Earth's surface, will form a San Andreas Fault Observatory at Depth (SAFOD). This project is part of the global EarthScope Project and will directly reveal, for the first time, the physical and chemical processes controlling earthquake generation within a seismically active fault. As Dr Mark Zobak, one of SAFOD’s principal investigators, told the BBC: ”It’s like using a stethoscope and listening very, very carefully”.
Fault-zone rocks and fluids will be retrieved for laboratory analyses, and geophysical measurements will be made within the active fault zone. SAFOD's long-term monitoring activities will include detailed seismological observations of small to moderate earthquakes and continuous measurements of rock deformation and other parameters during the earthquake cycle.
SAFOD will provide direct information on the composition and mechanical properties of rocks in the fault zone, the nature of stresses responsible for earthquakes, the role of fluids in controlling faulting and earthquake recurrence, and the physics of earthquake initiation and rupture. By observing quakes "up close," SAFOD will mark a major advance in the pursuit of a rigorous scientific basis for assessing earthquake hazards and predicting earthquakes.
Sources and Resources: United States Geological Survey (USGS), EarthScope, SAFOD
USGS’s website: http://www.usgs.gov
Safod’s website: http://earthscope.org/safod/
Parkfield Experiment http://quake.wr.usgs.gov/research/parkfield
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Each image is legally protected by U.S. and International copyright laws and may NOT be copied and used for reproduction in ANY manner without the explicit written authorization of Frédéric Neema. All pictures on this Web Site are copyrighted © Frédéric Neema and are for Web browser viewing only. All images on this website are registered with the U.S. Copyright Office. Any unauthorized download, screen capture, or otherwise captured or reproduced copy of any image or other content on this website is a violation of the Federal Copyright Law. The infringing party may be held liable for damages up to $150,000 per infringement plus all attorney's fees and legal costs