A drilling project that is harvesting 1,000 feet of earth and rock cores from the Los Angeles basin will establish a virtual library of information on the geology of the area, according to scientists from the U.S. Geological Survey (USGS).
The two-week project, which is a cooperative effort of the USGS and the Water Replenishment District of Southern California (WRD), got underway July 14, when a huge drill began turning out three-inch- diameter earthen cores that can be read like a book by earth scientists.
The information contained in the drill cores will help USGS and other scientists better understand the geological framework of the Los Angeles basin, in respect to which of the soil and rock layers might contain underground water and which are the most susceptible to shaking during earthquakes. "No one has done this kind of detailed and integrated work in the shallow subsurface of the LA basin before," said USGS hydrologist Eric Reichard. "When all of the analyses are complete, this will be the best described site in the region for understanding the flow of water and chemicals in the ground and for understanding why earthquakes cause more damage in some areas of the basin than in others."
USGS geologist Dan Ponti acknowledged that tens of thousands of oil walls, water wells and engineering test borings have been drilled into the shallow portion of the Los Angeles basin in the past 100 years, but unfortunately, the records and measurements from most of those wells are not detailed enough to answer some of the important questions that he and other scientists have about the history and material properties of the water-bearing sediments. "It's like not having all the pieces to a large jigsaw puzzle," Ponti said, "and these cores should help us find those missing pieces."
At the heart of the drilling project is a 31-ton drill rig operated by the USGS. Chewing its way through the relatively soft, unconsolidated sediments of the LA basin, the diamond-bit drill is expected to reach the 1,000-foot depth by July 23. The layers of material in the cores will yield information dating from the past few hundred years in the upper layers to more than a half-million years ago at the 1,000-foot depth.
Following the coring operation, sensitive instruments that can measure changes in water levels and the chemical characteristics of underground water will be installed in the drill holes and that data will be monitored by geologists, hydrologists and chemists at the USGS and hydrogeologists at the WRD.
Other instruments that can measure ground movements will be installed in the hole and monitored by scientists at the Southern California Earthquake Center (SCEC). "Being able to place instruments this deep is a real opportunity for us," said Dr. Jamison Steidl, a SCEC member and seismologist at the University of California at Santa Barbara. "Because ‘cultural noise' from traffic often interferes with interpretation of seismic signals obtained from surface and near-surface instruments, having these deep- set instruments will give us a much clearer picture of seismic wave propagation. This collaboration is a great opportunity for scientists to improve our ability to record the small earthquakes so that we can better image the faults under Los Angeles, improve our modeling of them and perfect our techniques for predicting future ground motion."
The cores that are being retrieved are being examined for various properties at a mobile laboratory next to the drill site. Following completion of the drilling project the cores will be moved to refrigerated storage at the USGS Western Region Center in Menlo Park, Calif. After more complete analysis there, they will be sent to the USGS National Core Library and Research Center in Denver, Colo., where more than one million feet of cores from 8,000 drill sites around the world are cataloged and available for examination by scientists from other government agencies, universities and the private sector.
As the nation's largest water, earth and biological science, and civilian mapping agency, the USGS works in cooperation with more than 2,000 organizations across the country to provide reliable, impartial scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, contribute to the sound conservation and the economic and physical development of the nation's natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.
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