[S-EM13] 地磁気・古地磁気・岩石磁気

[SEM13-P05] トンガ王国産津波巨礫の地磁気を用いた移動年代推定

*佐藤 哲郎¹、中村 教博²、長濱 裕幸³、佐藤 雅彦⁴、後藤 和久⁴、渡部 真史⁵、池田 暁³、佐竹 健治¹、Kula Taaniela⁶ (1.東京大学地震研究所、2.東北大学高度教養教育・学生支援機構、3.東北大学大学院理学研究科地学専攻、4.東京大学大学院理学研究科地球惑星科学専攻、5.中央大学理工学部都市環境学科、6.トンガ王国国土天然資源省)

キーワード：津波石、年代測定、残留磁気

Viscous remanent magnetization partially overprints the natural remanent magnetization in reworked boulders. The magnitude of such magnetization depends on the time passed since reworking, as well as ambient temperature, for which there is a well-known theoretical time-temperature relationship of remanent magnetization. Most references used the paleomagnetic dating protocol, which is applicable to single-domain particle assemblages, while experimental data often disagree with other dating applications (e.g., radiocarbon and U-series dating). Here, we use modified time-temperature relationship based on a stretched exponential relaxation function that accounts for the complex magnetic structures. Samples of tsunami boulders from the Kingdom of Tonga have chemical-viscous remanent magnetization, and their non-exponential relaxation is well fitted by the stretched exponential relaxation function. Combining the modified time-temperature relationship of remanent magnetization, which considers the observed stretching exponent value, and sea level change data, we estimate the reworked age of the tsunami boulders.