Investigations on Processing of Seismic Wave Forms (III) -Analysis of Wave Forms by Vector Orbit (II)-

Abstract

The method reported in Part II of this study is improved on. The resultant wave forms of the operational circuit are recorded directly on an; X-Y recorder. Though the principle is the same as in Part I, the experiment was done using two pairs of multipliers and integraters made by authors (Fig.1). The up-down motions of the recording-pen of the X-Y recorder was made at regular time intervals for the purpose of time mark. The processing was done in the two frequency ranges of 0.5 to 1.0 Hz and of 0.07 to 0.14 Hz.
The list of analyzed earthquakes and estimated di r e ctions of epicenters are given in Table 1. Directions of epicenters obtained from the three components of the initial P phase are also given in this table. Examples of records are shown in Figs.2 to 12. Figs.13 and 14 are drawn in accordance with the procedure described in Part II. The conclusions drawn from this analysis are as follows:
(1) Absolute values of deflections of directions of epicenters of near earthquakes are relatively small in cases where seismic wa v es of frequency ranges of 0.07 to 0.14 are analyzed, while t hose of distant earthquakes are relatively small in the case where seismic waves of frequency ranges of 0.07 to 0.14 Hz are analyzed. Due to slowness of response of the X-Y recorder, the frequency range of 1 to 2 Hz of seismic waves, where most favorable results were obtained for near earthquakes in Part II, is not analyzed in this case.
(2) As in Part II of this study, apparent directions of epicenters obtained by this analysis of earthquakes whose epicenters are northeast of Matsushiro deflect to the north from the true direction. Estimated epicenter directions from three components of the initial P phases show a similar tendency.
(3) Earthquakes whose initial P phases are observed in three components are picked up. Then directions of epicenters estimated from the initial P phases are compared with the direc t i ons of epicenters estimated with the method described in this report. These two kinds of estimated directions show no significant difference between them (Fig.15).
(4) Examples of results of the same procedure for the PP waves are shown in Fig.16. Deflections of estimated epicenter d irections from true directions are greater in PP waves than in P waves, the resultant curves of both types of waves show similar features.
(5) The S mark in Fig.2 shows the point corresponding to the initial S phases. If S waves consist of SH components, the direction of progress in orbit should be reversed and go towards the origin of the co-ordinate, at the initial Sphase. But as observed in Fig.2, the direction of progress is changed but not reversed in the actual orbit. This means S waves have not only SH components but also SV components.
(6) One of the practical applications of this study is the azimuth finder for the epicenter. We want to try to make this instrument for practical use.