Uncertainty of faulting for long-term safety assessment in geological disposal

Abstract

We classified the uncertainties in the mechanism and timescale of faulting for long-term safety assessment of the geological disposal of radioactive waste. We categorized faulting into three phenomena: (1) rupture of main active faults; (2) formation of splay faults; and (3) reactivation of existing faults. The reactivation of existing faults is classified into three types: (1) faults induced by earthquakes around the ones; (2) faults reactivated by the change of stress regimes from the large trench type earthquakes; and (3) faults reactivated by the change of regional stresses. The uncertainty in the frequency of faulting in the Kyushu-Ryukyu arc was classified into five different timescales: (a) <100 years; (b) a few hundred to a few thousand years; (c) a few thousand years to 1 Myr; (d) 1-2 Myr; and (e) >2 Myr. Identifying the temporal and spatial heterogeneities and factors in faulting are the keys to evaluating the uncertainty of faulting for safe, long-term disposal of radioactive waste.