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Upper mantle P structure on the ocean side of the Japan-Kurile Arc

Fukao, Yoshio (1977) Upper mantle P structure on the ocean side of the Japan-Kurile Arc. Geophysical Journal International, 50 (3). pp. 621-642. ISSN 0956-540X. doi:10.1111/j.1365-246X.1977.tb01338.x.

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Slowness measurements are made for the first and later arrivals of P waves from about seventy Kurile-Kamchatka earthquakes (13° < Δ < 30°) at the Wakayama Micro-Earthquake Observatory, Japan. The experimental error of dT/dd is not more than 3 per cent and the data points suffice to draw a dT/dΔ curve fairly uniquely. In the distance range 4° < Δ < 15° a travel-time curve, including a later arrival branch, is constructed for a specific Kurile event using the records along the Pacific coasts of the Japanese-Kurile islands. The results are inverted to obtain a velocity model for the upper 800 km of the mantle beneath the trench side of the Japan-Kurile Arc. The model includes a high-velocity lid extending down to 85 km depth. The low-velocity zone is of relatively high speed (8.1 km/s) and is terminated by a high-velocity gradient zone at depths 165-200 km, just below which the velocity is nearly constant with depth. The velocity increases very sharply near 400 km by about 6 per cent. An abrupt change in the slope of velocity occurs near 520 km. A major transition zone in the depth range 630-670 km consists of about 7 per cent increase in velocity and is sharp, especially near the base. A minor transition zone is tentatively suggested to exist around 740 km. Relative arrival times, crossover distances and qualitative amplitude behaviour calculated for this model are consistent with the observed data. Station residuals for the least-squares determination of dT/dΔ closely correlate with the local seismicity.

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Additional Information:© 1977 RAS. Received 1977 February 14; in original form 1976 September 20. I am indebted to all the staff at Wakayama Micro-Earthquake Observatory, Tokyo University for the use of the facilities and the seismograms. I thank Dr Sieji Ichikawa for allowing me to copy the JMA seismograms of the 1971 December 2 event. I also thank Drs Kenshiro Tsumura, Tetsuo Takanami, and Shigeki Horiuchi who kindly sent me the copies of the seismograms. Useful discussions with Drs Tokuji Utsu and Harumi Aoki are acknowledged. The final version of this paper was written while I was a Geophysical Research Fellow at Seismological Laboratory, California Institute of Technology. I am grateful for Drs Don L. Anderson, Hiroo Kanamori, and Donald V. Helmberger, who kindly read the manuscript and gave me various comments.
Group:Seismological Laboratory
Issue or Number:3
Record Number:CaltechAUTHORS:20170424-095430587
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Official Citation:Yoshio Fukao; Upper mantle P structure on the ocean side of the Japan—Kurile Arc. Geophys J Int 1977; 50 (3): 621-642. doi: 10.1111/j.1365-246X.1977.tb01338.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:76842
Deposited By: Tony Diaz
Deposited On:24 Apr 2017 17:08
Last Modified:15 Nov 2021 17:03

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