Surface Wave Polarization Anisotropy near the East Pacific Rise as Revealed from Group Velocities and Synthetic Waves
スポンサーリンク
概要
- 論文の詳細を見る
Anomalous dispersion curves of Rayleigh waves with group velocity maxima of 3.9 to 4.0km/sec at a period of 25 sec, near the East Pacific Rise, can be well explained by the upper mantle structure consisting of a very thin oceanic plate with a thickness of about 30 km and a low velocity zone with an extremely low shear velocity of 4.13km/sec. The Love wave response for the upper mantle structure is signigicantly different, namely group velocities of 4.30km/sec observed for periods from 20 to 110 seconds can be finely explained by a high shear velocity of 4.25km/sec in the low velocity zone. A surface wave polarization anisotropy of 3% in shear velocity is clearly present in the youngest region in the Pacific. If a volume fraction of involved molten pockets of 0.05 to 0.10 in the low velocity zone is assumed, the ratio of the minor to the major axes of an oblate spheriod of the molten pockets is estimated to be about one half. The surface wave polarization anisotropy in this region is inferred to be caused by the alignment of these partially molten pockets.東太平洋海膨付近に於ける周期25秒でレイリー波群速度の最大値3.9から4.0km/secを示す異状な分散曲線は,厚さおよそ30kmの非常に薄い海洋レプートと4.13km/secという非常に遅いS波速度からなる低速度層で構成される上部マントル構造によって良く説明される.このような構造に対するラブ波の応答は著しく異なる.即ち,周期20秒から110秒に於いて観測された群速度4.3km/secは低速度層における高いS波速度4.25km/secによって見事に説明される.水平と上下方向のS波速度の食い違いが3%という表面波のpolarization anisotropyは太平洋の最も若い地域で明瞭に存在する.低速度層における部分溶融状態のマグマポケットのvolume fractionの割合を0.05から0.10に仮定すると,部分溶融したポケットの扁球体の短軸と長軸の長さの比は約0.5と見積られる.このマグマポケットの配列が表面波のpolarization anisotropyを生成させていると推定される.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,Earthquake Research Instituteの論文
- 1984-12-25
東京大学地震研究所,Earthquake Research Institute, University of Tokyo,Earthquake Research Institute | 論文
- 16. Local Phenomena of Tsunami (Part 1)
- 20. Hydrated Aluminium-Sulphate Minerals from New Fumaroles on Volcano Yakeyama, Niigata Prefecture
- 24. Gases and Deposits from Fumaroles on the New Dome "Showa-Shinzan", Volcano Usu, Hokkaido, Japan
- 23. Surface Wave Polarization Anisotropy in the West Pacific as Revealed from Group Velocities and Synthetic Waves
- Surface Wave Polarization Anisotropy near the East Pacific Rise as Revealed from Group Velocities and Synthetic Waves