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Spatial distribution of earthquakes in the Kii peninsula, Japan, south of the Median Tectonic Line

Kanamori, Hiroo and Tsumura, Kenshiro (1971) Spatial distribution of earthquakes in the Kii peninsula, Japan, south of the Median Tectonic Line. Tectonophysics, 12 (4). pp. 327-342. ISSN 0040-1951. doi:10.1016/0040-1951(71)90020-5.

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Precise data obtained by a high-sensitivity micro-earthquake observatory network are used to determine simultaneously the crustal structure and the spatial distribution of small earthquakes in the Kii peninsula region, Japan. The spatial distribution of hypocenters thus determined clearly shows two distinct groups of earthquakes: (1) a group of shallow (H ⩽ 10 km) earthquakes on the western coast of the Kii peninsula near Wakayama; (2) a group of mantle earthquakes, having a depth ranging from 30 to 70 km and trending NE-SW, in the central part of the Kii peninsula. Along the trend of the second group, a marked structural anomaly is found which suggests the presence of a high-velocity zone at depths below 20 km. A projection of the hypocenters of the earthquakes belonging to the second group onto a vertical plane strikingNW-SE shows a wedge-like distribution to a depth of 70 km. The spatial relation between this wedge-like distribution and the 1944 Tonankai earthquake (M = 8.0) suggests a common tectonic process which is now taking place in the Kii peninsula region. The activity of the earthquakes of the first group terminates abruptly to the north at the Median Tectonic Line. This activity is represented by numerous but relatively small events (M < 5) without any conspicuous major earthquakes in history. It is suggested that the strength of the crust in this region of shallow activity is too weak to sustain stresses large enough to be released in a major event; rather, the stresses which probably originate from the tectonic activity represented by the earthquakes of the second group are released by numerous minor fracturings of the low-strength crust. A possibility of using the weak crust for detecting a remote stress accumulation is suggested.

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Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1971 Published by Elsevier B.V. Received 8 June 1971, We wish to acknowledge our indebtedness to Professors Kazuaki Nakamura and Setumi Miyamura for stimulating conversation. Assistance by Miss Tatoko Hirasawa is also gratefully acknowledged.
Group:UNSPECIFIED, Division of Geological and Planetary Sciences
Issue or Number:4
Record Number:CaltechAUTHORS:20150217-154031890
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Official Citation:Hiroo Kanamori, Kenshiro Tsumura, Spatial distribution of earthquakes in the Kii peninsula, Japan, south of the Median Tectonic Line, Tectonophysics, Volume 12, Issue 4, October 1971, Pages 327-342, ISSN 0040-1951, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:54894
Deposited By: Ruth Sustaita
Deposited On:18 Feb 2015 03:42
Last Modified:10 Nov 2021 20:39

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