Probabilistic Seismic Hazard Mapping Of IcelandProposed seismic zoning and de-aggregation mapping for EUROCODE 8

摘要

A few attempts of producing seismic zoning maps of Iceland have been carried out during the last fewdecades. The earlier efforts were mostly intuitive and based on iso-seismal maps produced from pastearthquakes. In the mid 1990s, an attempt was made to produce an iso-acceleration map based oncalculated peak acceleration from past earthquakes, using standard attenuation formulae. This map,which was wrought with many discrepancies, was produced as a National application document (NAD) inconjunction with adoption of Eurocode 8. It was clear, however, that the seismic zoning of the countrywas inadequate and much more research work was needed to provide a reliable earthquake risk map in theform of peak accelerations. The South Iceland earthquakes of the year 2000 provided a wealth ofinformation regarding measured peak accelerations, earthquake source mechanism and attenuation ofseismic waves. Moreover, an intensive study of past historical earthquakes has recently been carried outresulting in an upgraded earthquake catalogue for the whole country. Thus all the ingredients forproducing a reliable earthquake risk map for Iceland are in place.In this study, the earthquake catalogue has been extended by generation of future earthquake events inorder to prevent historical bias. Based on a new attenuation model for seismic waves, the peakaccelerations for the whole country have been calculated for a selected subset of the extended cataloguebased on Brune's source spectrum. Thus a fairly stable earthquake zoning map for the whole country hasbeen produced with 475-year peak accelerations. In addition, de-aggregation of this map has been carriedout to produce a magnitude and a distance map describing the dominating 475-year event. These maps canbe used as a basis for simulation of earthquake time histories at a certain site in concord with therequirements of the Eurocode 8.