ポータブル蛍光エックス線分析装置による津波堆積物の簡易判別手法の検討

Abstract

To improve a method for geochemically discriminating paleotsunami deposits, a quantitative analysis of major and trace elements in boring cores from the Shizuoka plain on the Pacific coast of central Japan was performed using a portable energy dispersive X-ray fluorescence spectrometry system (portable XRF). Geochemical approaches using a portable XRF contribute to studies on simple and rapid methods for detecting paleotsunami deposits. Calibration curves for quantitative analyses were prepared using 25 geochemical standard samples. Geochemical characteristics of paleotsunami deposits (ca. 1000, 3500, and 4000 cal BP) from the Shizuoka plain were obtained. Most of the quantitative data collected with the portable XRF were good agreement with reported values measured with stationary-type energy dispersive XRF in previous studies. Therefore, a portable XRF was applied in geochemical studies of samples from the Shizuoka plain. Relatively high Si/Ti, Ca/Ti, and Sr/Ti atomic ratios were observed in paleotsunami deposits from layers aged ca. 1000, 3500, and 4000 cal BP. Moreover, relatively high Cr/Ti ratios were found in lower paleotsunami deposits (ca. 4000 cal BP). Fe/Ti and S/Ti ratios increased in peaty clay layers just below the paleotsunami deposits in the core. On the other hand, Cl was not detected in the cores. Most of the paleotsunami deposits were distinguished from other layers in the cores using a cluster analysis with the portable XRF data. Therefore, a portable XRF is useful for characterizing paleotsunami deposits from the Shizuoka plain.