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In a paper read yesterday to the American Geophysical Union, L. Don Leet, director of the Harvard University Seismograph Station, revealed his entirely new earthquake theory which explains for the first time, shocks originating miles beneath the earth's crust.
The theory was developed as a result of extensive study at the Lake Ossipee, New Hampshire, earthquake which took place last December, From this quake the best records ever obtained near the center of an earthquake are available.
Rocks Will Break
The discovery that rocks under great pressure will break as well as flow, which is the basis of the new hypothesis, was made by David T. Griggs, a junior fellow at Harvard, Dr. Leet said.
Hitherto, scientists have believed that in the so-called "area of flow" miles beneath the earth, under the terrific confining pressures, the rock would remain in a state of flow and would not break.
Minor Shocks Occur
According to the new theory, which postulates that the rocks may break in deep quakes where confining pressure is great, the flowing rock breaks and quickly heals again. In the surface quakes, the break is not healed, and readjustments occur as hundreds of minor shocks.
In the Ossipee earthquake, the center of disturbance was 21 miles below the surface, and the quake came as a result of a sudden break in the rock. The second shock at Lake Ossipee was probably due to a gigantic underground rebound from the first, Dr. Leet said.
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