Patterns in seismology and palaeoseismology, and their application in long-term hazard assessments – the Swedish case in view of nuclear waste management

Abstract

Seismic events are recorded by instruments, historical notes and observational criteria in geology and archaeology. Those records form a pattern of events. From these patterns, we may assess the future seismic hazard. The time window of a recorded pattern and its completeness set the frames of the assessments. Whilst instrumental records in seismology only cover decades up to a century, archaeoseismology covers thousands of years and palaeoseismology tens of thousands of years. In Sweden, covered by ice during the Last Ice Age, the palaeoseismic data cover some 13 000 yr. The nuclear industries in Sweden and Finland claim that the high-level nuclear waste can be buried in the bedrock under full safety for, at least, 100 000 yr. It seems hard, if on the whole possible, to make such assessments from the short periods of pattern recognition in seismology (< 100 yr) and palaeoseismology (∼ 13 000 yr). All assessments seem to become meaningless, maybe even misleading. In this situation, we must restrict ourselves from making too optimistic an assessment. As some sort of minimum level of the seismic hazard, one may multiply the recorded seismic hazard over the past 10 000 yr by 10, in order to cover the required minimum time of isolation of the toxic waste from the biosphere of 100 000 yr.