Colorado earthquakes and active faults

Ninety two potentially active faults have been identified in Colorado since the 1960s with many areas of the state still unexamined. Five hundred and seventy Colorado earthquakes have been felt or have had magnitudes of 2.0 or greater between 1870 and 2005. Eighty four earthquakes have equaled or exceeded an MMI Scale of V. Colorado's largest historical earthquake, which occurred on November 7, 1882, had an MMI of VII to VIII and an estimated magnitude of 6.6 Mw. Colorado's MCE is estimated at 7.5 ML. Thirteen Quaternary faults have MCE's >= 6.25. Analysis of instrumentally measured independent earthquakes predicts that a 6.5 ML or larger earthquake has a mean recurrence interval of about 420 years. A 7.5 ML earthquake has a 2 percent Poisson's probability of exceedance in 50 years. The western two-thirds of Colorado, which includes the Front Range, have a significant potential for damaging earthquakes.