May 19, 2003
Contact: Dr. Charles Rubin (509-963-2827/fax 509-963-1109/e-mail charler@geology.cwu.edu)
ELLENSBURG, Wash. - The magnitude 7.9 earthquake along the
Denali fault in Alaska on Nov. 3, 2002, generated 210 miles of surface
rupture -- one of the largest ever recorded on U.S. soil, and was
similar to the 1906 San Francisco magnitude 7.8 earthquake on the San
Andreas Fault in California.
Investigations of the earthquake rupture, reported in the May
16 issue of “Science” in an article titled “The 2002 Denali Fault
Earthquake, Alaska: A Large Magnitude, Slip-Partitioned Event,”
indicate the success of earthquake hazard models while also shedding
light on the complex processes of large surface-rupturing earthquakes.
The earthquake caused more than $40 million in damage to
roads and airstrips, but with only a few scattered settlements in the
region, there was little building damage and no fatalities.
“It was a significant opportunity to understand the
consequences of a very large earthquake to prepare for the time when
one will happen in a much more densely populated area,” Dr. Charles
Rubin, CWU geological sciences department chair, says.
Rubin and two colleagues, Dr. Kerry Sieh, California
Institute of Technology geology professor, and Dr. George Plafker, a
researcher emeritus with the U.S. Geological Survey (USGS) Western
Region Western Earthquake Hazards Team, went to Alaska to assess the
extent of surface rupture caused by the quake. Their investigations
showed that the details of the rupture in space and time are key to
understanding damage.
To rapidly document this earthquake, Rubin, Sieh and Plafker
were aided by researchers from the University of Alaska Fairbanks,
Alaska Division of Geological and Geophysical Surveys, Humboldt State
University and University of California Berkeley in making observations
that will aid in understanding the genesis and effects of future large
earthquakes along the San Andreas Fault.
The Denali fault ruptured beneath the trans-Alaska pipeline,
and surveys indicate there was about 18 feet of horizontal offset at
the site. Fortunately, geological studies of the fault prior to
construction led to a special design that would have allowed for an
even greater shift without pipeline failure. The pipeline withstood
the 2002 earthquake with little damage and no oil spillage,
demonstrating the value of pre-construction geotechnical studies in
earthquake risk mitigation.
The large magnitude earthquake produced stronger ground
shaking and effects for locations in the direction of rupture, actually
causing damage to houseboats on Lake Union, in Seattle, from sloshing
caused by seismic surface waves.
The Denali Fault is a 700-km long fault, but only the central
section broke in 2002, increasing the stress on the adjacent faults,
bringing those segments closer to failure. The likelihood of rupture
depends upon previous earthquake history. The documentation of prior
events on those faults is now under way, according to Rubin.
