Structure of the Earth's Crust in the Continents

Abstract

In 1910 A. Mohorovičić published the first paper in which arrival times of elastic waves from a near-by earthquake were used to calculate the velocity of earthquake waves in the earth's crust, He found for longitudinal waves a velocity of 5.4 km/ sec in the upper 50 km and a velocity of about 7.8 km/sec below that. Earthquake records from other regions furnished similar results and indicated one or more intermediate layers. Later, when artificial explosions were recorded, it was found that the velocity in the uppermost layers is appreciably higher than that found from earthquake records. Data are available now for parts of Europe and the United States. They indicate a velocity of about 6 km/sec immediately below the sedimentary layers, increasing (in some regions) to as much as 61 km/sec at a depth of about 10 km. The Mohorovičić discontinuity is found in general at a depth between 30 and 40 km, and the velocity below it is between 8.1 and 8.2 km/sec. The discrepancy between the results from earthquake waves and those from artificial explosions is beyond the limits of error. This new interpretation is suggested to explain all observations.

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