June 3, 2004

Boise State Scientist Conducts Geophysical Studies On Seattle Fault

Geophysical experiments that could lead to a better understanding of the earthquake hazards associated with a fault in the Seattle area will be conducted this month by researchers from Boise State University and the U.S. Geological Survey. Lee Liberty, a geophysicist with the university’s Center for Geophysical Investigation of the Shallow Subsurface (CGISS), received a $90,000 grant from the USGS’s National Earthquake Hazards Reduction Program for the project. He will collaborate with Thomas Pratt of the USGS. Boise State University students, geosciences students from the University of Washington, and community volunteers will assist with the work. “We hope to answer fundamental questions about the geometry of the Seattle Fault to assess the potential for earthquake hazards in the region,” said Liberty. “We also hope to better understand past earthquakes related to this fault.” The Seattle Fault bisects the Seattle, Bellevue and Lake Sammamish, Wash. areas and may extend further east and west. Recent research has revealed that at least one major earthquake occurred along the fault about 1,000 years ago — a short time span in geological terms. Faults that have moved in the past 10,000 years are classified as active, Liberty said. “The potential [for an earthquake] is real,” said Liberty. “If we can understand the hazards, we will be better able to assess whether building codes and other infrastructure in the area are adequate.” The Seattle Fault is a crustal fault and depending on its length, damage from an earthquake may be localized over a small area or widespread, Liberty said. His project should provide new information about how far the fault extends to the east, and also how fault segments may interact with each other. The experiments will take place June 7-29 along residential streets, private property and rights of way in the Bellevue, Sammamish and Issaquah areas. They will involve using a seismic vibrator truck and ground-listening microphones called geophones to obtain a subsurface image of the fault, said Liberty. Although the truck generates some noise and a very small ground motion can be felt up to a few feet away, no damage will occur from either the truck or the geophone sensors, Liberty said. The work will not interrupt traffic flow or interfere with routine business operations. The 12,000-pound vibrator truck is a scaled-down version of vehicles used in oil exploration. The vibrator truck and geophones will travel approximately one mile each day along road sections in the area. Researchers will plant the geophones in the ground with 3-inch spikes, and will then connect each geophone with a cable and vibrate the ground surface with the vibrator truck along the adjacent roadway. The experiments will yield seismic data that researchers can interpret to better understand the fault characteristics and the potential earthquake hazards, Liberty said. Liberty has used similar seismic reflection techniques on other research projects, including ongoing projects in Portland, Ore. and Boise. More information on the experiments, including maps and updated information can be found on the Web at http://cgiss.boisestate.edu Contact Lee Liberty Boise State University lml@cgiss.boisestate.edu 208 426-1166 Media contact Janelle Brown communications and marketing jbrown2@boisestate.edu 208-426-1790