Historical Review of the Study on Intermediate and Deep Earthquakes

The deep earthquake was first detected by Herbert Hall Turner in 1922, and confirmed by Wadati in 1928, Scrase in 1931 and Stechschulte in 1932. Wadati demonstrated the inclined intermediatedeep earthquake zone under the Japanese islands and neighborhoods in 1935. Such earthquake zones were found in other areas in the circum-Pacific regions. Benioff (1954) classified them morphologically into two types, and ascribed them to thrusts, following Suess's idea. Richter (1958) critisized the thrust hypothesis, as most of deep earthquakes were not accompanied by reverse faults, but by normal faults which were deduced from the initial motion of P-waves. Gutenberg and Richter (1954) pointed out the regular arrangement of geology and geophysical phenomena from an outer oceanic trench to an inner belt of deep earthquakes in the circum-Pacific region. Wadati (1928) demonstrated the vertical relation between shallow earthquakes and deep ones in central Honshu of the Japanese islands. Suzuki (1975) showed a similar relationship in northeast Honshu, and suggested the role of vertical deep faults. Bemmelen (1972) attributed the inclined intermediate-deep earthquake zone to the upward driving force derived from the deep mantle. Suzuki et al. (1978) tried a simulation experiment using the finite element method to propagate the inclined intermediate-deep earthquake zone by the differential vertical displacement at the base of mantle, and the result was compared with the earthquake-generating stresses.