Abstract
THE fourteenth number of the Publications in European languages issued by the Earthquake Investigation Committee of Japan is entirely devoted to a profusely illustrated paper on the modulus of rigidity of rocks, by Mr. S. Kusakabe. The experiments, which are a continuation of investigations made by Prof. H. Nagaoka on the elastic constants of rocks, relate entirely to torsion, and show, amongst other things, that even for very small strains Hooke's law does not hold, that in the relationship of stress to strain, or twisting couple to twist produced, rocks, exhibit a marked hysteresis, and that the modulus of rigidity of a rock in its virgin state is greater than is usually supposed. Inferences to be drawn from these important investigations (in which stresses are applied slowly) are that waves of small amplitude are propagated with a higher speed than those with a large amplitude (increase an amplitude ten times and the velocity is reduced to half or one-third), also in a strained medium, as, for example, along a mountain chain, velocity is somewhat increased. In view of the first of these inferences, Mr. Kusakabe does not see the necessity to assume that the tremors of an earthquake follow paths different from that of the large waves or shocks. Whether we agree or disagree with this suggestion, we can congratulate the author on his important memoir, which is a new leaf in seismo-metrical research.
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Seismological Notes . Nature 69, 160–162 (1903). https://doi.org/10.1038/069160b0
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DOI: https://doi.org/10.1038/069160b0