Seattle Fault Zone -- 900-930 AD earthquake larger than previously thought

May 30, 2012

A fresh look at sedimentary evidence suggests the 900-930 AD rupture of the Seattle fault possibly produced a larger earthquake than previously recognized. The Seattle fault zone, a series of active-east-west trending thrust faults, poses seismic threat to the Puget Sound region.

The 900-930 AD rupture is the only known large earthquake along the Seattle Fault, making geological records of prehistoric events the only clues to the earthquake potential of the fault.

While a graduate student at the University of Washington, Maria Arcos looked at tsunami and debris flow deposits – both evidence of a paleo-quake – in the coastal marsh at Gorst, Washington. She also identified evidence of at least three meters of uplift that preceded a , which was followed by a sandy debris flow from Gorst Creek, and suggests that the 900-930 AD quake covered a greater geographic area than previous fault interpretations.

The revised height and width of deformation caused by the quake may influence current interpretations of the Seattle fault's structure. This study found a minimum of three meters of uplift at Gorst, which is double the amount of previous fault models for the same location. A broader zone of deformation, says Arcos, may indicate either a wider zone of slip along the dip of the , a shallower dip or splay faults farther to the south.

Explore further: Research gives glimpse of tectonic history on Puget Sound-region fault zones

More information: "The A.D. 900 – 930 Seattle Fault Zone Earthquake with a Wider Coseismic Rupture Patch and Postseismic Submergence: Inferences from New Sedimentary Evidence," published in BSSA, Vol 102:3; DOI:10.1785/0120110123

Related Stories

Why do earthquakes stop?

February 6, 2008

The underlying structure of a fault determines whether an earthquake rupture will jump from one fault to another, magnifying its size and potential devastation. Understanding why some earthquakes terminate along a fault, ...

Loma Prieta fault not so weak?

December 19, 2007

A new study adds to evidence that the fault responsible for the 1989 Loma Prieta earthquake is not as unusually weak as had been thought.

NASA study of Haiti quake yields surprising results

October 14, 2010

(PhysOrg.com) -- The magnitude 7.0 earthquake that caused more than 200,000 casualties and devastated Haiti's economy in January resulted not from the Enriquillo fault, as previously believed, but from slip on multiple faults ...

Recommended for you

Sea ice extent sinks to record lows at both poles

March 22, 2017

Arctic sea ice appears to have reached on March 7 a record low wintertime maximum extent, according to scientists at NASA and the NASA-supported National Snow and Ice Data Center (NSIDC) in Boulder, Colorado. And on the opposite ...

Under the dead sea, warnings of dire drought

March 22, 2017

Nearly 1,000 feet below the bed of the Dead Sea, scientists have found evidence that during past warm periods, the Mideast has suffered drought on scales never recorded by humans—a possible warning for current times. Thick ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.