Abstract
THE last publication of the Earthquake Investigation Committee of Japan, issued this year, is of special nterest to those engaged in seismometry. In it Prof. A. Tanakadate describes a vertical motion seismometer, in which a mass is so suspended that it is not affected by tilting or iy horizontal shocks, and remains in neutral equilibrium or vertical displacements of considerable magnitude. Until his instrument was devised, for large earthquakes at least, vertical spring seismographs, and for that matter horizontal oracket seismographs, have responded to the changes in nclination of their supports, with the result that they have behaved as clinographs, and components of vertical and horizontal movements have not been faithfully recorded. Mr. Imamura gives results relating to the speeds at which earthquake motion has been propagated over the Tokio area. At four stations, from 2 to 10 kilometres apart, and connected by telegraph, seismographs were arranged each of which gave an open diagram on a surface marked by time intervals sent from the Seismological Institute. From the differences in time at which the same wave was recorded at different stations, the speed of that wave was determined. The surface velocity arrived at is that V = 3.28 + 0.05 kilometres per second, but as to whether different waves in the same earthquake travel with the same speed, which we think is not the case, we are left in darkness. In a paper on after shocks, Prof. Omori shows that the expected or calculated number of such settlements for a given period closely accords with observation. By maps and diagrams he also shows the space distribution of after shocks, there being, as might be expected, fewer of these disturbances recorded at places distant from a focusthan at those comparatively near.
Article PDF
Rights and permissions
About this article
Cite this article
Seismological Notes . Nature 67, 473–474 (1903). https://doi.org/10.1038/067473b0
Issue Date:
DOI: https://doi.org/10.1038/067473b0