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タイトル: Residuals of Teleseismic P-wave Travel Times Observed in Japan
その他のタイトル: 日本で観測される遠地地震のP波走時残差
著者: Maki, Tadashi
著者(別言語): 牧, 正
発行日: 1982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57冊第2号, 1982.9.30, pp. 151-191
抄録: Anomalies in teleseismic P-wave travel-times observed at stations in Japan have been studied by using 8920 arrival time data of 223 distant earthquakes. Earlier arrivals are observed at stations on the Pacific side of Northeast Japan, and later arrivals are observed at stations in Southwest Japan and on the Japan Sea side of Northeast Japan. Exceptionally early arrivals are observed at stations in the Chugoku region, Southwest Japan. The geographical distribution of the station anomalies in the teleseismic travel times is consistent with the features of seismic activity, Bouger gravity anomaly, heat-flow and attenuation of seismic waves. Sinusoidal variations of the teleseismic travel-time residuals with azimuth are observed. Especially at high-sensitivity stations in the Kanto region the time differences of up to 2 seconds are observed between the earliest and latest arrivals. These azimuthal variations can not be explained only by the regional variation in the crustal structure directly beneath the stations. Mean residuals of the teleseismic travel times at each station are more in conformity with the station corrections of travel-times determined by the joint hypocenter determination (JHD) method for the mantle earthquakes rather than for the crustal earthquakes. Regional and lateral variations of the travel-time anomaly are mainly interpreted by the presence of a high-velocity zone in the upper mantle, associated with the descending slab beneath the Japanese Islands from the Pacific side. A negative correlation is observed between the mean residuals of teleseismic travel times and the Bouguer gravity anomalies at each station. Lateral variation of the velocity and density is suggested from the negative correlation of azimuthal variation of teleseismic residuals and the Bouguer gravity anomaly around some stations. A tendency of separation of stations into two groups with earlier and later arrivals is observed in the relation of the station anomalies with the station corrections of travel times and earthquake magnitude, and the Bouguer gravity anomaly. Regional differences of the attenuation of seismic waves seem to be consistent with the station anomalies of teleseismic travel times.
URI: http://hdl.handle.net/2261/12841
ISSN: 00408972


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