Abstract Large earthquakes leave telltale geological evidence that can be identified and used to provide a better understanding of local and regional seismic risk. This evidence complements the instrumented record of earthquakes. In regions such as western Canada, which have only a brief history of settlement, the geological record may provide evidence of larger or different types of earthquakes than have occurred historically. The geological signature of even strong earthquakes, however, is subtle. Primary evidence of past earthquakes is geomorphic or stratigraphic in nature and is produced directly by ground rupture or coseismic land-level change.
Secondary evidence is a product of ground shaking or tsunamis.
These features have been used successfully to identify and map active and potentially active faults in many areas, for example California and Japan. However, caution is required in inferring a seismic origin for scarps in areas of moderate and high relief, as they may be produced by gravitational movements rather than earthquakes. Faults that experience only rare earthquakes may not have a particularly strong surface expression due to surface weathering and erosion. Some of these limitations are overcome by searching for offset strata in sediment fills that extend across faults. The common approach is to dig trenches at sites where faults are draped by geologically young, stratified sediments.