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Published January 1972 | public
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Determination of effective tectonic stress associated with earthquake faulting. The Tottori earthquake of 1943

Kanamori, Hiroo ORCID icon

Abstract

The records of the Tottori earthquake of 1943 (M = 7.4, 35.5° N, 134.2° E, depth 10 km) about by a low-magnification seismograph at a relatively short distance are used to determine dynamics fault parameters such as the particle velocity and the effective tectonic stress, in addition to static fault parameters such as the dislocation and the stress drop. The particle velocity of the fault motion is determined by comparing the initial slope of the observed seismogram with that of synthetic seismograms. Resolution sufficient for determining the rise time is obtained. The effective stress is determined from the particle velocity in the light of several dynamics fault models developed recently. The fault parameters thus determined, with supplementary data on the P-wave first motion, the aftershock and the triangulation, are: fault, type, vertical right-lateral strike slip; fault dimension, 33 km (length) × 13 km (width); strike, N 80° E; rupture velocity, 2.3 km/s (bilateral); average dislocation, 2.5 m; seismic moment, 3.6 × 10^(26) dyne · cm; rise time 3 s; particle velocity of the fault plane, 42 cm/s; stress drop, 83 b; effective tectonic stress, 30 to 100 b. The approximate agreement of the stress drop with the effective stress suggests that this earthquake represents an almost complete release of the effective tectonic stress. The seismic slip, 2.5 m, is in approximate agreement with the slip determined from the triangulation data over a period of 66 y, suggesting that the rate of the strain accumulation is very small in the epicentral area, the Japan Sea coast side of Honshu, Japan.

Additional Information

© 1972 Published by Elsevier B.V. Received 1 February 1972, Revised 3 March 1972. Professor Kennosuke Okano at the Abuyama Seismological Observatory of Kyoto University kindly provided me with the seismograms used in this study and valuable information concerning the instrument constants. Dr. Yutaka Sato at the Geographical Survey Institute of Japan kindly allowed me to use his unpublished data on the triangulation survey. Professor Syunitiro Omote at Kyushu University offered me, on my request, a revised map of the aftershock distribution. Conversations held with Professor Kazuaki Nakamura of the Earthquake Research Institute of Tokyo University and with Dr. Yozo Hamano of Geophysical Institute of Tokyo University were very helpful in completing this work. Dr. Yoshiaki Ida of the Massachusetts Institute of Technology kindly sent me a preprint of his latest work with Professor Keiiti Aki. Dr. Masaji Ichikawa of the Meteorological Research Institute provided me with the original data on the P-wave first motions. Dr. M. Trifunac of Lamont-Doherty Geological Observatory of Columbia University sent me a preprint of his latest paper on the San Fernando earthquake of 1971. To these colleagues I express my sincere thanks. I am also very grateful to Miss Tatoko Hirasawa for her assistance throughout this study. The computer time was provided from the Japan UNIVAC Co. as University contribution (UNICON).

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