SEISMIC GAPS IN SPACE AND TIME

Abstract

Large, shallow earthquakes along plate boundaries account for the largest release of seismic energy worldwide. Studies of seismic gaps provide valuable insight into this process and are also the cornerstone of earthquake prediction research. Not only have the locations and sizes of earthquakes been successfully identified prior to their occurrence, but these same locations have also provided a focus for fundamental research regarding the earthquake process. In addition, the identification of seismic gaps provides an opportunity for public planning to mitigate future disasters caused by earthquakes. The concept of seismic gap originated with empirical observations in Japan in the 1920s, and was later provided with a physical basis by the theory of plate tectonics in the 1960s. Today, studies of seismic gaps involve detailed analyses of the sizes and source rupture processes of earthquakes, as well as the characteristics of fault zones (e.g. fault geometry, inferred heterogeneities, seismic vs aseismic slip along fault zones) and detailed geologic studies documenting the repeat times of fault rupture in recent geologic history. One of the simplest and clearest definitions of a seismic gap is given by Aki (1978):