Statistics play an increasing part in the role of forecasting the probabilities of where and when future hazards such as volcanic events may occur. Spatio-temporal models allow forecasts of where volcanoes are most likely to form over designated timescales in specific regions. Owing to the long performance periods required of geological repositories for radioactive wastes (see Chapman et al., Chapter 1, this volume), this type of forecasting is especially relevant in repository siting projects in regions that are clearly prone to volcanism. This chapter looks at a key component of forecasting the spatio-temporal likelihood of volcanism in Japan where a site for a geological repository for high-level waste is being sought, using an open volunteer process that potentially opens up large parts of the country for consideration. The constraints on siting a repository are that it should have an extremely low probability of being directly impacted by future magma intrusion in the next 10 ka, with the probability of such events over a 100 ka timescale (possibly out to 1 Ma) being an important aspect of the safety assessment of potential sites.

The context of the work reported in this chapter is a case study of the Tohoku region of northeast Japan. Our aim is to develop a generic methodology to assist with the definition of spatio-temporal probabilities of future volcanism and associated magmatic disruption of a repository. The choice of this area for a case study is illustrative.