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タイトル: Upper Mantle Structure from Apparent Velocities of P Waves Recorded at Wakayama Micro-Earthquake Observatory.
その他のタイトル: 和歌山微小地震観測所で観測されたP波のみかけの速さとマントル上部の構造
著者: Kanamori, Hiroo
著者(別言語): 金森, 博雄
発行日: 1967年11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45冊第3号, 1967.11.30, pp. 657-678
抄録: Direct measurements of apparent velocities, d⊿/dt, of P waves are made for about fifty earthquakes recorded at Wakayama Micro-Earthquake Observatories for the distance range 5° to 55°. The main features of the variation of d⊿/dt are as follows. d⊿/dt≒8.0 km/sec (5°<⊿<12°), d⊿/dt≒8.8 km/sec (15°<⊿<19°), d⊿/dt≒12.8 to 13.0km/sec (27°<⊿<40°). The transition from the 8km/sec branch to the 8.8km/sec branch is relatively abrupt. A clear discontinuous change of d⊿/dt is observed at ⊿=19.3°, followed by a rapid increase from 9.8 to 12.5km/sec up to ⊿=25°. Amplitude becomes very small around ⊿=15°, and at 16°<⊿<22° a large later phase is observed. To explain the observed apparent velocity data, a preliminary velocity-depth model with the following major features is derived. The velocity is almost constant, about 7.9km/sec, down to 150km depth where it rapidly increases to 8.3km/sec. Another rapid velocity increase starts at the depth of 375km. Below 430km the velocity variation with depth is midway between those of the Jeffreys and the CIT11CS3 models. Travel-time residual from the Jeffreys-Bullen Table for the preliminary model is consistent with those determined by explosion and earthquake studies. The velocity increase at the depth of 150km is difficult to explain by a simple pressure and temperature effect on a homogeneous mantle. Compositional change or partial melting or both may have to be invoked. The rapid velocity increase at the depth of 375km is in good harmony with the idea of the olivine-spinel transition of (Mg,Fe)2SiO4. The temperature at this level can be estimated as 1300 to 1500℃ for a reasonable composition of the mantle. Earthquake energy release which takes a maximum value at this level in the Japan region may be attributed to the same cause and may have an important bearing on island arc tectonics.
1965年1月から6月の間に和歌山微小地震観測所網で観測されたP波のみかけの速さ, C,を調べた.用いた地震は和歌山からの距離5°<⊿<55°のもので,次の結果が得られた.
URI: http://hdl.handle.net/2261/12351
ISSN: 00408972
出現カテゴリ:東京大学地震研究所彙報
東京大学地震研究所彙報

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