Physical Sciences: Terrestrial Spectroscopy by a Cryogenic Gravity Meter

Abstract

LATE in the nineteenth century and early in the twentieth century, British scientists such as Lamb¹ and Love²had made theoretical predictions about the free oscillations of the Earth. The gravest mode was calculated to be about 1 h. Benioff³ in 1954 surmised that a signal with a 57 min period recorded during the Kamchatka earthquake might be the grave mode of the free oscillations of the Earth. Pekeris⁴ and his colleagues, stimulated by such predictions, were able to calculate the period of free oscillations of the Earth for a large number of modes, and these theoretical predictions were confirmed for the first time^5,7 after the great Chilean earthquake of May 22, 1960. Easier numerical integration techniques for calculating different models of the Earth have since been introduced⁸ and other earthquakes—among them, the Kurile Islands earthquake⁹ of October 13, 1963, the great Alaskan earthquake¹⁰ of 1964 and the Rat Island (Aleutians) earthquake¹¹ of February 4, 1965—have confirmed some of the observations made during the Chilean earthquake. Recently, it has been possible¹² to record the spheroidal oscillations of the Earth from earthquakes of magnitude 6.5.