23. Surface Wave Polarization Anisotropy in the West Pacific as Revealed from Group Velocities and Synthetic Waves
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Multi-mode Love waves across the west Pacific have been analyzed in detail, to investigate the surface wave polarization anisotropy. From the inversions of group velocities and wave forms of observed and theoretical seismograms, it is found that the shear wave velocity in the low velocity zone under the regions corresponding to the ocean-floor age of 90～150m.y. is 4.43km/sec, which is 2～3% higher than values estimated from Rayleigh waves. This discrepancy is caused by the existence of partially molten materials and by the preferred orientation of crystal axes of olivines within the asthenosphere. From the wave form analyses two types are found in the wave forms of Love waves. One forms isolated waves and the other merely oscillated waves showing no clear normal or anomalous dispersions. The latter type presents a few peculiar dispersion curves with exceptionally high and low group velocities of 4.9 and 4.1km/sec respectively around a period of 70 seconds.表面波異方1生を研究する為に,西太平洋を伝播した基本及び高次モードラブ波を詳しく解析した.観測された波と理論記象の波形,及び群速度のイソバージョンから次の事が明らかになった。即ち,海底年代が九千万年から一億五千万年に相当する地域の低速度層のS波速度は4.43km/secであり,これはレイリー波から求められている値より2～3%高い.この食い違いはアセノスフェア内における部分溶融相の存在と橄欖石等の結晶軸の定向性によって生じている.波形解析よりラブ波の波形には二つの形状がある事が見い出された.一つは孤立波であり,他の一つは正分散も逆分散もせず単に振動している波群である.後者のタイプでは,周期70秒付近で群速度が4.9km/secとか4.1km/secとか例外的に高い値や低い値をもつ異常な分散曲線を示すものが若干みられた.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,Earthquake Research Instituteの論文
- 1984-01-14
東京大学地震研究所,Earthquake Research Institute, University of Tokyo,Earthquake Research Institute | 論文
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