Pacific Northwest at risk for mega earthquake
Undersea fault behaves much like the one that broke
offshore in Chile
By Alicia Chang
updated 12:44 p.m. MT,
Tues., March. 2, 2010
ANGELES - The disaster in Chile has brought new
attention to an undersea fault along the Pacific
Northwest capable of producing the same type of mega
earthquake and inflicting heavy damage on bustling
cities like Seattle, Portland and Vancouver.
fault has been dormant for more than 300 years, but when
it awakens — tomorrow or decades from now — the
consequences could be devastating.
last rupture unleashed the largest known quake to hit
the Lower 48 — a magnitude-9 that sent tsunami waves
crashing into Japanese coastal villages.
computer simulations of a hypothetical magnitude-9 quake
found that shaking could last 2 to 5 minutes — strong
enough to potentially cause poorly constructed buildings
from British Columbia to Northern California to collapse
and severely damaging highways and bridges.
quake would also send powerful waves rushing to shore in
minutes. While big cities such as Portland and Seattle
would be protected from severe flooding, low-lying
seaside communities may not be as lucky.
Pacific Northwest "has a long geological history of
doing exactly what happened in Chile," said Brian
Atwater, a geologist with the U.S. Geological Survey and
University of Washington. "It's not a matter of if but
when the next one will happen."
Pacific Northwest fault behaves much like the one that
broke offshore Chile that triggered a magnitude-8.8
quake. Shaking lasted 2½ minutes and the temblor
destroyed or badly damaged 500,000 homes.
Located just 50 miles off the coast, the 680-mile-long
Cascadia fault is part of several seismic hotspots
around the globe where plates of the Earth's crust grind
and dive. These so-called subduction zones give rise to
mountain ranges, ocean trenches and volcanic arcs, but
also spawn the largest quakes on the planet.
There's an 80 percent chance the portion of the fault
off southern Oregon and Northern California would break
in the next 50 years and produce a megaquake.
odds of rupture are lower for the northern end, mainly
including Washington state and Vancouver island, with a
27 percent chance during the same time period, according
to calculations by Chris Goldfinger who heads the Active
Tectonics and Seafloor Mapping Laboratory at Oregon
Research presented last year at a seismology conference
found that Seattle's high-rises built before 1994 when
stricter building codes took effect were at high risk of
collapse during a megaquake.
Disaster managers in Oregon and Washington are aware of
the risks and work is ongoing to shore up schools,
hospitals and other buildings to withstand a seismic
definitely being proactive in trying to get those fixed,
but we have a long way to go," said Yumei Wang,
geohazards team leader with the Oregon Department of
Geology and Mineral Industries.
has 1,300 schools and public safety buildings that are
at high risk of collapse during a major quake. The state
recently doled out $15 million to two dozen schools and
emergency facilities to start the retrofit process.
State law requires that all poorly built public safety
buildings be upgraded by 2022 and public schools by
state is also helping its coastal communities — home to
100,000 residents — plan for vertical evacuation
buildings that could withstand giant tsunami waves.
Seattle plans to retrofit its 34 fire stations. The city
is also working on a plan to upgrade 600 buildings
considered most at risk.
have been preparing aggressively," said Barb Graff, who
heads the city's Office of Emergency Management.
Chilean quake occurred in an offshore region that was
under increased stress caused by a 1960 magnitude-9.5
quake — the largest recorded in history, according to
geologist Jian Lin of the Woods Hole Oceanographic
Similar tectonic forces are at play off the Pacific
Northwest where the Juan de Fuca plate is diving beneath
North America. At some point, centuries of pent-up
stress will cause the plates to slip. Scientists cannot
predict exactly when a quake will occur, only that one
region is all too familiar with violent earthquakes. In
2001, a 6.8-magnitude quake centered near Olympia,
Wash., rattled a swath of the Pacific Northwest, but
remarkably caused no deaths. While it was not the type
of quake that hit Chile, it was a reminder of how a big
disaster could strike at any time.
better understand megaquakes, a group of scientists
planned to travel to Chile in May for a conference on
giant earthquakes and their tsunamis. There are field
trips planned to commemorate the 50th anniversary of the
1960 Chile quake.