Instantaneous Instrumental Seismic Intensity and Evacuation

The earthquake that occurred on October 6, 2000 in western Tottori, Japan is an interesting event because residents living in houses that completely collapsed had time to evacuate. The period which people had time to escape from collapsing buildings was due to the particular aspect of ground shaking. Escape time is another important variable besides building resistance, indoor environment, hour of the day, type of human activity at the time of the earthquake, that must be taken into account. To measure this new variable, a measure and a model that indicate the time available for evacuation are proposed. The measure of transitional characteristics of ground motion is presented as Instantaneous Instrumental Seismic Intensity (IISI). The duration of ground motion is modeled for several periods, which characterize human behavior and the surrounding situation. The evacuation time available defined as the period from when people start to feel the shaking until they cannot move at all, is measured by the IISI. An application that indicates the threshold of the time available to evacuate is examined together with the hypocentral distance and the earthquake ’ s magnitude for practical future use.