Reanalysis of seismic low velocity zones based on a pre-melting model.

2020 Fiscal Year Final Research Report

• Project/Area Number: 17H02951
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Solid earth and planetary physics
• Research Institution: The University of Tokyo
• Principal Investigator: Takei Yasuko 東京大学, 地震研究所, 教授 (30323653)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: premelting / 粘弾性 / 非弾性 / 地震波減衰 / 地震波低速度域 / アセノスフェア

Outline of Final Research Achievements

Thermodynamic model of grain boundary developed for binary eutectic system predicts shows that the pre-melting occurrence can be expected in the Earth’s upper mantle. Based on the realistic volatile distribution and solidus profile obtained from a model of fractional decompression melting, we have shown that even when the oceanic upper mantle is melt free, geotherm sufficiently approaches the solidus at various plate ages, causing the lithosphere-asthenosphere system. We further clarified the quantitative effects of melt on anelasticity and developed a new anelasticity model which can be applied to a region with relatively large melt fraction (several percent). We also measured the impurity effects on anelasticity, and examined the similarities and differences between impurity effects and pre-melting effects.

Free Research Field

固体地球科学

Academic Significance and Societal Importance of the Research Achievements

本研究により、メルトが全くなくてもプレメルティングによってリソスフェアアセノスフェア構造が作られることが示された。この成果は、上部マントルにおける地震波低速度域の存在を、僅かな量のメルトしか存在しないとする地球化学的観測結果と整合的に理解することを可能にするという点で非常に大きな意義がある。また、地震波特性という高周波域から、粘性という長いタイムスケールまでの超広帯域での岩石物性を、室内実験データに基づいて予測した点にも、大きな学術的進歩がある。