In order to understand the earthquake hazard in an area, one must know what the earthquake history has been.
Because the interval between large earthquakes on any given fault is often in the neighborhood of hundreds or even thousands of years, it is necessary to study when large earthquakes have occurred on the faults themselves. These studies of faults fall under the category of paleoseismicity, or the study of ancient earthquakes.
By studying the geologic characteristics of faults, geoscientists can often determine when the fault last moved and estimate the magnitude of the earthquake that produced the last movement. In some cases, it is possible to evaluate how frequently large earthquakes occurred on a specific fault during the recent geological past.
Trenching is a common technique for investigating an active fault with a surface rupture, carefully excavating a series of trenches to reveal the structure and magnitude of the fault displacement.
Paleoseismic studies are most commonly performed when a critical facility is in the planning stages, such as a dam or a power plant. For example:
- The Ken Caryl fault and Kennedy fault trenches were excavated to study earthquake hazards that might affect the construction of the Two Forks Dam.
- The Golden fault was extensively studied as part of the due diligence for building the Rocky Flats Technology Site (the official name for the cleanup operation).
- The Rampart Range fault trench was excavated to determine risks associated with construction of the Air Force Academy water treatment plant.
Please use the Paleoseismic Studies Map to interactively select and locate information about paleoseismic research in the State of Colorado.
For additional information on the faults that have ruptured within the last 23 million years in Colorado visit the CGS Interactive Earthquake and Fault Mapserver.
Please Note: Blue lines on these two maps depict faults that offset Quaternary deposits (less than 2 million years) at a 1:250,000 scale. The location is approximate and should not be used to determine proximity to the actual fault.
Colorado Geological Survey