Abstract

In the National Seismic Hazard Maps, the U.S. Geological Survey (USGS) uses ground‐motion models (GMMs) appropriate for both the central and eastern United States (CEUS) and the western United States (WUS) for the Rocky Mountains and Colorado plateau, which includes much of Colorado and Wyoming, eastern Utah, northeastern Arizona, and northwestern and eastern New Mexico. Geologically and geophysically, much of this region is more similar to tectonically active regions to the west. To evaluate the validity of this approach, we analyzed earthquake source (stress parameter), path (frequency‐dependent Q), and site parameters (kappa) for 24 earthquakes of M 1.5–3.3 that have been recorded at 84 seismic stations in the southern Rocky Mountains (SRM) of central Colorado. Based on a broadband inversion methodology using the Levenberg–Marquardt algorithm, we obtain an average estimate of the stress parameter of 9.7 bars, an average Q0 of 196, and kappa estimates ranging from 0.005 to 0.03 s. These values are more consistent with typical values found in the WUS and not the CEUS. These results suggest that the use of GMMs for tectonically active regions such as the WUS is more appropriate for use in seismic hazard analyses in regions such as the SRM. Furthermore, our results coupled with several other studies argue that the boundary used by the USGS in the National Seismic Hazard Maps should be located further to the east to at least align with the traditional boundary separating the Rocky Mountains and the Great Plains.

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