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: A 5.3-million-year record of sea level and temperature

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

add to favorites email to friend print save as pdf

Related Stories

Why do earthquakes stop?

Feb 06, 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?

Dec 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

Oct 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 ...

Recommended for you

Image: Grand Canyon geology lessons on view

2 hours ago

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of ...

First radar vision for Copernicus

3 hours ago

Launched on 3 April, ESA's Sentinel-1A satellite has already delivered its first radar images of Earth. They offer a tantalising glimpse of the kind of operational imagery that this new mission will provide ...

User comments : 0

More news stories

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

First radar vision for Copernicus

Launched on 3 April, ESA's Sentinel-1A satellite has already delivered its first radar images of Earth. They offer a tantalising glimpse of the kind of operational imagery that this new mission will provide ...

Image: Grand Canyon geology lessons on view

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of ...

Book offers simplified guide to shale gas extraction

The new book, "Science Beneath the Surface: A Very Short Guide to the Marcellus Shale," attempts to offer a reader-friendly, unbiased, scientific guide needed to make well-informed decisions regarding energy ...

Net neutrality balancing act

Researchers in Italy, writing in the International Journal of Technology, Policy and Management have demonstrated that net neutrality benefits content creator and consumers without compromising provider innovation nor pr ...