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The P-curve and the S-curve resulting from a study of the Tango Earthquake, Japan, March 7, 1927

Abstract

The records of the Tango earthquake, for which the co-ordinates of the epicenter and the origin time are well defined and whose focus is shallow, furnish data which define the P-curve with considerable precision to an epicentral distance of about 8°. From that point to 50° the curve is fixed in position by very few points. The values given by Byerly for the Montana earthquake have influenced the author in placing the curve as reported for this range. Such a placing is demanded also, to some extent, by the earlier and the later parts of the curve. As so placed, it lies considerably below the Mohorovii-Macelwane P-curve for much of the range, the maximum difference being about nine seconds. It is certain that the latter curve gives P—O intervals much too great near the center of this range, but it would be desirable to make a detailed study of some other earthquake whose epicentral position, origin time, and depth of focus could be well defined and for which the last named would be shallow, the earthquake being so situated that well-equipped stations would register the disturbance for distances within this range.

From 50° to 60° the control is better, but there are still too few points to fix its position as definitely as could be desired.

From 60° to 100° there are many control points of considerable strength. This section of the P-curve seems fixed in position within narrow limits. Data for distances beyond 101° are lacking.

Footnotes to the tabulations for both the P-curve and the S-curve are given in some detail as showing the relative strength of controlling points.

In the case of the S-curve, there seems to be no well-defined departure from the curve published in mimeographed form by Macelwane in 1926. The footnotes explain outstanding departures from this curve. It may be said that the Tango earthquake data support the previously published S-curve to within the limits of accuracy of the observations.

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