Earthquake scenarios: a practical way to handle alternative solutions to historical earthquakes and to increase the transparency of seismic hazard assessment

Abstract

This study presents a way to handle historical earthquakes whose parameters are based on sparse documentary materials. It is recommended that discrete earthquake scenarios should be constructed in such cases. Scenarios are possible sets of parameters for a past earthquake, reconstructed on the basis of the macroseismic data available. A probability value is to be attached to each of them using expert judgment. This means that uncertainties associated with historical earthquakes become discrete instead of continuous. Assigning a probability value to each scenario and including alternative solutions in the catalogue makes decision-making more transparent. The current state of the art of the research on a given historical earthquake is documented. It is illustrated how seismic histories of a given place are altered when different scenarios of historical key earthquakes are taken into account. The seismic histories consequently have different probabilities. The choice of an appropriate seismic history could be governed by the need: For example, for a high-risk facility, the high-intensity histories have to be considered. Different earthquake scenarios included in the catalogue would permit to evaluate also the uncertainty of the activity rate and to construct the final logic tree.