Application of a Bayesian approach to assess the probability of concealed active faults existing from multiple geological datasets

ベイズ推論を用いた未知の活断層の存在に関する確率論的評価

Martin, A. J.*; 浅森 浩一; 石丸 恒存 ; 梅田 浩司

Martin, A. J.*; Asamori, Koichi; Ishimaru, Tsuneari; Umeda, Koji

変動地形の明瞭でない活断層、いわゆる未知の活断層の存在を把握するための手法は、概要調査等において必要不可欠な技術である。これまで未知の活断層の存在の可能性については、すでに認識されている活断層の分布密度から評価されてきた。本研究では、2000年鳥取県西部地震の余震域を事例として、活断層の分布密度に加えて、未知の活断層に関連する複数の地球科学的情報(断層ガスのヘリウム同位体比や地殻応力の主軸方向)を、ベイズ推論により考慮した確率分布を計算した。

Assessing the stability of the geological environment including the spatio-temporal distribution of active faulting is of particular concern in the context of site selection of a radioactive waste repository. In order to assess the spatio-temporal distribution of active faults, one typically starts by looking at mapped active faults to estimate spatial frequencies and orientations. However, active faults listed in current databases do not represent a complete picture of active faulting, as not all active faults have a surface reputure, and their existence might be unknown. In this case, additional datasets are needed that may imply the existance of active faulting. The Bayesian approach can be used to construct probablistic models from mulitple datasets in order to assess the likelihood of given natural phenomena occuring over defined time periods. We have been developing such a Bayesian model for new active fault segment formation in the Western Tottori district as a case study.