A REVIEW OF LONG-RANGE EARTH STRAIN MEASUREMENT TECHNIQUES FOR PROVIDING EARTHQUAKE WARNING

摘要

One of the most valuable tools for studying earthquakes and faults is earth strain or displacement measurements. Geologists are now looking for minute telltale dis¬placements that might occur before an earthquake. This report discusses the possible accuracies that might be achieved by three different electromagnetic measurement techniques: 1) Microwave phase measurements, 2) Modulated light beam, and 3) Laser interferometers. The first is extremely sensitive to propagation errors. The second can achieve a modest degree of accuracy, 10-7 or better, and will clearly meet the minimum requirements. The third will provide by far the greatest degree of accuracy for propagation path lengths over which at least a partial degree of coherence of the wave front can be maintained.