Nov. 20, 2008
Seismometers Spy Under Rockies
Over the last year, nearly 60 earthquake recording instruments, called seismometers, have been installed throughout Colorado as part of a national experiment to learn more about the structure of the Earth beneath North America. The instruments will remain in place for two years before being removed and then re-deployed in another state.
The instruments installed in Colorado are part of EarthScope, a program funded by the National Science Foundation to explore the structure and evolution of the North American continent and the physical processes controlling earthquakes and volcanoes.
Anne Sheehan, a professor of geophysics at the University of Colorado at Boulder and an active participant in this nationwide experiment says that "scientists can make seismic tomographic images of the subsurface using the data recorded by these instruments." Similar in concept to a medical CT scan, the seismic images can see miles and miles into the Earth. These images sometimes reveal faults and other structures that were previously unknown. In Colorado, the images will help scientists understand the structure beneath the Rocky Mountains and the Rio Grande Rift.
Although earthquakes in Colorado are not very frequent, a magnitude 6.5 event occurred in north-central Colorado in 1882, and fault scarps near the Great Sand Dunes provide evidence that large earthquakes in Colorado have occurred in the geologic past. The highly sensitive seismometers will record ground motion from earthquakes in Colorado - even earthquakes so small they cannot be felt by people - and from many earthquakes that occur around the world over the next two years. These data will help scientists determine the background levels of seismicity, including which faults might be active, so an assessment of seismic hazard near the faults can be made.
The earthquake recording stations in Colorado are part of a 400-station array that is gradually rolling across the United States from west to east over a 10-year period. The instruments are placed 70-km (~43 miles) apart in a grid-like fashion and will occupy more than 1600 sites before moving to Alaska.