著者

田中 豊

出版者

京都大学防災研究所

雑誌

京都大学防災研究所年報 (ISSN:0386412X)

巻号頁・発行日

no.8, pp.91-108, 1965-03-01

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In the direction of the horizontal displacements of the triangulation points, tilt variationsalways show the most remarkable mode as the crust behaves over a wide area the see-sawmotion decreasing amplitude and period with time, accompanying earthquakes at its peaks.The first stage of anomalous crustal movements before earthquake corresponds to thismode, so it appears characteristically in the direction of the horizontal displacement, in otherexpression, it may be also the direction related to the tectonic force. The second stage isthe movements of the strain concentration, so the ground tilts toward or opposite to theepicenter, relating to the earthquake mechanism. The third stage just before earthquake isthe pro:ess of rapid increase of creep or beginning of fracture, perhaps foreshock-occurrecne, so that the tilt variations increase their own rate in the same motion as the second stage nearthe epicenter, or reverse their direction at a far distance from the epicenter according to thebeginning of energy release. After the earthquake these anomalous movements continueuntil the termination of the aftershock activities.These stages and phenomena appear remarkably in the case of shallow earthquakes, anda little differently in the case of intermediate earthquakes.