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タイトル: Regional Variation of Pn Residuals and Its Application to the Location of Earthquakes in and around the Kanto District
その他のタイトル: Pn走時残差の地域的変化
著者: Maki, Tadashi
著者(別言語): 牧, 正
発行日: 1981年9月30日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第56冊第2号, 1981.9.30, pp. 309-346
抄録: Regional variation of the crust and uppermost mantle structure in Japan was estimated from the analysis of Pn arrivals. Travel-time curves represented by the cubic equation were separately fitted to 83 well-observed shallow earthquakes which occurred in and around the Kanto district by taking into account the velocity gradients with depths. Pn velocities vary from 7.4 to 8.1 km/sec and velocity gradients with depths have a mean of 0.007 km/sec per km. Residuals from the fitted travel-time curves show some systematic geographical features, i. e. early arrivals on the Pacific Ocean side of Northeast Japan and late arrivals on Southwest Japan and on the Japan Sea side of Northeast Japan. Such features are closely correlated with the regional variation of the crustal thickness derived from the Bouguer gravity anomaly and the surface dispersion. Hypocenters of 4865 earthquakes occurring in and around the Kanto district during the 16 years from 1963 to 1978 have been relocated by correcting the mean Pn residuals at each station. Focal depths have been determined to a tenth of a kilometer instead of the 10 or 20 km step employed by JMA. Relocated epicenters show a tendency of clustering in smaller regions. A low Pn velocity of about 7.4 km/sec was observed for the Middle Gifu Prefecture earthquake of September 9,1969. The travel-time curve for this earthquake requires lower velocities by about 0.4 km/sec over the entire depth down to about 100 km than those for the Ichikawa and Mochizuki (1971) model. An exceptionally low Pn velocity of 7.1 km/sec was observed for an earthquake occurring near Sado Island, Niigata Prefecture. Its velocity profile suggests either the absence of the normal velocity jump around the Moho discontinuity or the existence of the unusually thick "intermediate layer".
URI: http://hdl.handle.net/2261/12808
ISSN: 00408972


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