Scientists assess potential earthquake hazards along known faults by studying past earthquakes that have occurred along those faults. Because earthquake recurrence intervals may be hundreds to thousands of years for any given fault, the number of earthquakes directly observed on that fault in recorded history is typically one or two at most. Paleoseismologists (geologists who study past earthquakes) can dig further back in time by looking at the geologic record of ancient earthquakes: evidence of past slip events that have disturbed rocks and sediment around the fault. This is an expensive and time-consuming process that involves excavating parts of a fault, mapping out geologic structures, and determining the absolute dates of materials disturbed by past ruptures. An alternative approach is to study indirect evidence of past earthquake ruptures preserved in the fractured and pulverized rocks surrounding faults in the so-called fault “damage zone”. A fundamental question in this research project is whether fault damage zones contain information about the maximum earthquake size a fault can host (Mmax) in terms of type, style, extent, width and degree of damage. This project will develop criteria to distinguish damage related to earthquake rupture from damage accrued over the longer-term growth of the fault, and to use these criteria to test the hypothesis that the style and intensity of damage on faults that experience earthquake magnitudes greater than ~Mw6.6 to 6.8 can