日本地球惑星科学連合2015年大会

講演情報

インターナショナルセッション(口頭発表)

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT03] Structure and dynamics of Earth and Planetary deep interiors

2015年5月26日(火) 11:00 〜 12:45 106 (1F)

コンビーナ:*芳野 極(岡山大学地球物質科学研究センター)、田中 聡(海洋研究開発機構 地球深部ダイナミクス研究分野)、趙 大鵬(東北大学大学院理学研究科附属地震・噴火予知研究観測センター)、亀山 真典(国立大学法人愛媛大学地球深部ダイナミクス研究センター)、John Hernlund(Earth-Life Science Institute, Tokyo Institute of Technology)、座長:田中 聡(海洋研究開発機構 地球深部ダイナミクス研究分野)、河合 研志(東京大学大学院総合文化研究科広域科学専攻)

12:09 〜 12:12

[SIT03-P07] フレンチポリネシア下のP波速度異常

ポスター講演3分口頭発表枠

*大林 政行1吉光 淳子1杉岡 裕子1伊藤 亜妃1一瀬 建日2塩原 肇2末次 大輔1 (1.D-EARTH, JAMSTEC、2.ERI, Univ. Tokyo)

キーワード:トモグラフィ, プルーム, マントル, フレンチポリネシア

The French Polynesian region is characterized by positive topographic anomalies of 700 m, a concentration of hotspot chains. Many seismic tomography results show a broad low-velocity anomaly in the lower mantle continued from the base of the mantle. These observations suggest that a large-scale mantle flow rises from the bottom of the mantle beneath the region. Joint Japanese-French broadband seismological observations were performed from 2001 to 2005 with 10 island stations from the Polynesian PLUME project (Barruol et al. 2002) and 10 broadband ocean bottom seismometers (BBOBSs) from the Polynesian BBOBS project (Suetsugu et al. 2005). A P-wave
tomography using the data from these projects revealed that large-scale low-velocity anomalies (on the order of 1000 km in diameter) from the bottom of the mantle become smaller-scale low-velocity anomalies (on the order of 100 km in diameter) at the depth of about 1000 km. However the connection of the small-scale low-velocity anomalies to the surface hotspots was not unrevealed because of the poor resolution in the upper mantle.
A new P-wave tomography with better resolution in the upper mantle was obtained by adding data from BBOSBSs around Society Islands deployed along the TIARES project during 2009 - 2010 (Suetsugu et al. 2012) and by taking the finite frequency effect into account for the frequency-depended differential travel times. The frequencydepended differential travel times were measured by multi-band cross correlating P waveforms. The new P-wave tomography shows strong low-velocity anomalies beneath the Society Islands and Pitcairn in the upper mantle although they do not extend to the 660-km discontinuity. This model also shows that small-scale low-velocity anomalies in the uppermost lower mantle. The low-velocity anomalies in the depth range about 550 - 900 km are smaller both in lateral area and amplitude than those in most of the upper mantle and the lower mantle. The velocity patterns are well correlated each other in the depth range but are not correlated with the patterns above and below, indicating the mantle beneath the French polynesia can be divided into 3 layers in terns of radial correlation.