Nodata
The database contains no known Quaternary faults (younger than 1.6 million years) in this region because geologists have not found any faults that young that are at the Earth's surface.
Earthquakes occur in every state, more frequently in some than in others. Many parts of the US have not been settled long enough for us to have developed a clear understanding of how often damaging earthquakes occur there. Accordingly, this database is part of a large effort to determine the frequency of large, prehistoric earthquakes, to supplement the short historical record of earthquakes and thereby to reduce the uncertainties in hazard assessments.
Earthquakes occur by sudden movement on faults deep in the Earth's crust. Earthquakes larger than about magnitude 6 can rupture from those depths upward to the surface. This database summarizes surficial geologic evidence of faults that have ruptured during the Quaternary.
The most common kinds of surficial evidence are (1) Quaternary geologic strata that are offset across faults, and (2) Quaternary liquefaction features formed when strong earthquake shaking caused water-saturated sand, a few meters below the surface, to liquefy and erupt upward onto the surface. Many faults older than Quaternary are known in this region, but young movement on them has not been proved. In some areas, particularly east of the Rocky Mountains, the evidence of young offsets and liquefaction might have been destroyed by erosion or glaciation, buried under younger deposits, or be equivocal. Thus, faults with Quaternary movement but not in the database are possible in the region, and, if future work provides the missing proof, they can be added to the database.
