Probing the earth's crust, deeply.

Probing the earth's crust, deeply

At least 24 research projects will begin with the drilling thisfall of a 5-kilometer-deep, 15-centimeter-wide hole at Cajon Pass in southern California, scientists announced recently. Building upon previous investigations into shallower holes, the Cajon Pass hole is pat of a trend in geological research to probe deeper into the earth's crust.

Geologists participating in the project will retrieve coresamples and use in-hole sensors to examine the physical and chemical nature of rock formations, measure the stress on the rock, trace the relationship between pore pressure and earthquakes, investigate shifts in the earth's magnetic polarity and determine the temperature of the rock and fluid found in the hole. Their findings, they say, will contribute to earthquake prediction models, a greater understanding of crustal plate movement, the search for hidden mineral resources and the effort to find sites appropriate for nuclear waste disposal in the earth's crust. The project brings together researchers from several universities and is coordinated by Deep Observation and Sampling of the Earth's Continental Crust, Inc. (DOSECC), in Washington, D.C.

Ultra-deep holes--holes deeper than 6 kilometers--are nowin the planning stage in the United States and several European nations and promise deeper probing of interactions between the crust and the mantle lying beneath it. Two ultra-deep holes in the Soviet Union already exist, but Soviet scientists have released no news about the deepest hole -- 12.6 kilometers -- since early this year, says DOSECC president G. Arthur Barber. He says the silence "makes one suspicious" and has led to speculate that the pipe inside the hole may have sheared off. If so, the broken pipe remaining inside the hole is blocking any further drilling and will have to be "fished out."