Unlocking the mystery of earthquakes

Friday, November 1, 2002

At approximately 9:40 p.m. last Monday night, U.S. Geological Survey (USGS) officials and The University of Memphis Center for Earthquake Research and Information (CERGI) faculty conducted an experiment south of Payneway, on land owned by Ritter and Company. Researchers hope data obtained will help explain how the soil of the Delta affects how the ground shakes during an earthquake.

A well was dug 160 feet into the ground for 2600 pounds of explosives, which were detonated to produce the equivalent of a very small earthquake with a magnitude of 2.0 on the Richter scale.

Dr. Chuck Langston, from The University of Memphis CERGI, explained that eight sensors called K2 Accelerometers or accelerographs placed at the site measured waves from the blast. 80 permanent CERI stations in the Tennessee, Missouri and Arkansas region also recorded the blast. The central receive for this area is located at the Ritter Grain Elevator.

Earth scientists and engineers agree that the very thick sand and clay soil that blanket the Mississippi embayment should significantly affect the way seismic waves travel and therefore, how the ground shakes during an earthquake, said Butch Kinerney, of USGS. The precise nature of how these sediments affect shaking remains almost pure speculation because of the lack of instrumentally recorded data and the relatively low rate of earthquake occurrence in the region. Although we can improve instrumentation, changing the rate of earthquake occurrence remains beyond even the best scientist's capabilities. This experiment will do the next best thing -- create earthquake or seismic' waves -- by using artificial sources (explosions) instead of waiting for an earthquake, said Kinerney.

The recordings from this experiment will provide a wealth of information about sedimentary properties. This information is essential to builders, developers and the insurance industry to endure that the hazard potential of sedimentary deposits are factored into land use planning. Government agencies, universities and private organizations are working to increase awareness of the earthquake threat and to reduce loss of life and property in future shocks, said Kinerney.

The USGS is working with CERI and state and local agencies to better understand central U.S. earthquakes and to reduce loss of life and property in future shocks. Earthquakes pose one of the greatest risks for casualties and costly damage in the United States.

Langston said this event was one small part of the experiment. In-depth information about the experiment may be found on Langston's website at http://www.ceri.memphis.edu/~langston.

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