October 18, 2002
Albany County Earthquakes- the rest of the story
According to Jim Case, head of the Geologic Hazards Section at the Wyoming State Geological Survey (WSGS), although Albany County is one of the most seismically active areas in the eastern two thirds of Wyoming, it doesn't begin to compare to Yellowstone National Park or Teton County. Albany County has a moderate seismic hazard, as stated in a Laramie Boomerang article on October 13, 2002, but its seismic history and future potential cannot be discounted. Historically, there have been a number of earthquakes in or near Albany County, some of which have caused damage. All of those earthquakes have occurred on deeply buried active faults.
Earthquakes generally occur when faults activate or move. In Albany County, there are no exposed active faults, such as the Teton fault at the base of the Teton Range, so the only evidence we have of active and potentially active faults is the historic earthquake record. As such, there are buried faults that have activated near Laramie in 1898, 1931, and 1935. In 1954, an earthquake occurred 12 miles north-northeast of Laramie. It is estimated that the earthquake was felt over 2000 square miles. In Laramie, buildings shook and dishes fell from tables. One Laramie resident thought that the earthquake was an explosion. At Fox Park, a slow motion was observed by all residents. Doors and dishes were rattled, and a post supporting the roof of one house was shifted. At the town of Albany, a rapid motion was felt, with furnishings shifted and windows rattled. The earthquake was reported to have been felt for two minutes at Albany and in Centennial, the earthquake was described as being similar to a heavy dynamite blast. In Jelm, a rapid motion that lasted for ten seconds was felt by all residents. In Cowdrey, Colorado, a rapid motion was felt for fifteen seconds, and hanging objects swung. A few aftershocks were reported in Fox Park and Jelm.
A number of earthquakes have occurred in the Woods Landing, Fox Park, and Jelm areas of Albany County. The largest were reported in 1954, 1955, 1958, and 1959. The 1959 event cracked a concrete block building under construction.
There has been a long history of earthquakes in northern Albany County. Many residents remember the damaging magnitude 5.5 earthquake that occurred in October, 1984. The event was felt in seven states, and cracked a number of buildings. Hundreds of earthquakes have occurred in this same area, with recorded activity ranging from 1938 to the present. Again, the activity is occurring on deeply buried (12 to 16 miles deep) active faults.
A model for what can occur in the region is tied to a magnitude 6.5 earthquake that occurred between Laramie and the Fort Collins area in 1882. While such a large earthquake does not occur often, it must be taken into account in any hazards analysis. If it were to occur closer to Laramie today, there would be damage to buildings. Unfortunately, no one can predict when such an event may occur near Laramie – it could happen next week or it may not happen for many hundreds of years.
An increased awareness of the hazards posed by earthquakes can only benefit residents. The Geologic Hazard Section at WSGS has just completed a seismological characterization of Albany County. A copy of this report is available at Albany County Library and at the WSGS. Residents are encouraged to directly read about the seismic history and future earthquake potential of Albany County.
from the Office of the Wyoming State Geologist
Ron Surdam, State Geologist