Earth stress and seismic hazard from the size-frequency distribution of seismic events

An important component of being able to assess the hazard associated with naturally-occurring or induced earthquakes, is a prediction of the likelihood and size of the largest earthquake that could occur in a region. The size-frequency distribution of seismic events, also known as the b value is found to be consistent globally since the seismology community has been measuring and maintaining earthquake data; for this general population of earthquakes b=1. The fact that the b value can vary when earthquake population subsets are made by time, location, and method of occurrence, has led workers to seek a causal relationship to explain that variability by suggesting parameters related to earth stress, hypocenter depth, fluid pumping rate (in the case of induced earthquakes), for example. This paper uses three case studies to propose that the main determinant of the b value is the pre-existing fault and fracture character of the regional geology. Showing this relationship to be true allows the use of surface and subsurface geological mapping to serve as a proxy for earthquake occurrence and prediction of seismic hazard.