An Assessment of Colorado Seismicity from a Statewide Temporary Seismic Station Network

Abstract

Knowledge of the seismic hazard in Colorado is limited due to the short historical record of seismicity, the lack of permanent seismographic coverage, and the existence of human-induced earthquakes (Matthews 2003). The rate of seismicity in Colorado is characterized as low to moderate (Kirkham and Rogers 1981), yet the state has a history of occasional large-magnitude events (M > 5.5) (Talley and Cloud 1962; Kirkham and Rogers 2000), including an earthquake with estimated moment magnitude of 6.6 in north-central Colorado in 1882 (McGuire et al. 1982; Spence et al. 1996). Perhaps the best-known earthquakes in Colorado have been those induced by the disposal of waste fluids at the Rocky Mountain Arsenal near Denver (Evans 1966; Healy et al. 1968; Herrmann et al. 1981) and secondary oil recovery in western Colorado at the Rangely oil field (Gibbs et al. 1973). Earthquake swarms in Colorado are not uncommon: a swarm of earthquakes occurred in August and September 1986 near Crested Butte, with at least 200 events and a maximum magnitude ( ML ) of 3.5 (Bott and Wong 1995); another swarm of earthquakes occurred in the fall of 2001 near Trinidad, with a maximum magnitude of 4.6 (Meremonte et al. 2002). There is evidence of Quaternary tectonic activity of faults throughout Colorado ( e.g. , McCalpin 1986), with 14 faults with an assigned Maximum Credible Earthquake magnitude of M 6.25–7.5 (Widmann et al. 1998). These faults indicate potential for much larger earthquakes than those recorded to date (Matthews 2003). The occurrence of earthquakes has been documented in a variety of areas in Colorado, but in most cases the seismograph station coverage has been spatially limited to specific regions (see, e.g. , Goter and Presgrave 1986; Keller and Adams 1976; Bott and Wong 1995; Sheehan 2000; …