Time-Decreasing Hazard and Increasing Time until the Next Earthquake

Abstract

Contrary to common belief, as the time since the last earthquake in a certain region increases, the risk of occurrence of another earthquake diminishes. As a consequence, the expected waiting time to the next event increases with the elapsed time, in other words, the event moves away to the future faster than we move. This paradoxical phenomenon is found in regions as diverse (from a tectonic point of view) as California, Japan, New Zealand, Spain or the British Islands, as well as in worldwide scales. This behaviour shows a surprising regularity, since in all the cases it is well described by the same universal scaling functions. This universality suggests the existence of a common simple physical mechanism in the earthquake generation process.