DETERMINISTIC HAZUS DAMAGE ESTIMATES FOR EARTHQUAKES ON SELECTED FAULTS IN COLORADO AND THE IMPORTANCE OF Q (ATTENUATION FACTOR)

Because so little is known about earthquake hazard in Colorado, probabilistic evaluations give very low values for expected damage if an earthquake did occur somewhere in the state. This study looks at the actual damage that would be expected if earthquakes of varying magnitudes were to occur on selected Quaternary faults in the state. The results demonstrate that emergency managers across the state need to be aware of the consequences of an earthquake in their area and incorporate it into disaster planning.

An evaluation of a M 6.0 earthquake at the Rocky Mountain Arsenal provides an instructive tool for demonstrating the power of FEMA's HAZUS software in helping emergency managers plan for the consequences of an actual earthquake. The analysis indicates economic losses >$12 billion, 15,370 households displaced, and >4,000 casualties. Maps show the locations of damage to various types of facilities: bridges, hospitals, airports, schools, gas facilities, police and fire stations, etc. Acceleration maps for a repeat of the 1882 (Mw 6.5) earthquake agree quite well with the mapped intensities from the actual earthquake, thus supporting the conclusion that the epicenter was near Estes Park. A repeat of that earthquake would create $2.5 billion in economic losses.

These analyses emphasize the importance of gaining a better understanding of the attenuation factor (Q) in Colorado. The USGS hazard maps use both the western U.S. (WUS) and eastern U.S. (CEUS) Q factors for different parts of Colorado. Scenarios on each fault were run using both CEUS and WUS Q values supplied in HAZUS. The damage results are three to five times greater for the CEUS scenarios.