ÇorUani» ffibeem r
July 21,1999
Focus
Page 3
$ M ia i J10
And that’s not the only fault in
By J. L. Clark and Yumei Wang
the
area. There’s also the East Bank
Contributing Writers from Oregon
fault
(running along the east bank of
Dept. Of Geology and Mineral
the Willamette River in north Port
Industries
land, the Oatfield fault (crossing from
ere you shaken up by the ‘Spring Milwaukie to the west slopes of the
Break Quake’ in 1993? Maybe West Hills), the Lacamas fault (think
Lacamas Lake in Vancouver), and
you were in town onjuly 15'h and July
2"d and felt these earthquakes. If you the Mt. Angel fault (which triggered
were in just the right place, you might the magnitude 5.6 Spring Break
have felt a very small one last Febru Quake).
T hat doesn’t even count the
ary'. As you can tell, feeling an earth
Cascadia
subduction zone, a fault
quake in Portland isn’t exactly com
that
runs
off
the Oregon coast that
mon, but it’s certainly not rare.
“If you know what you’re look could produce a magnitude 8 to 9
ing for, there’s a lot of evidence earthquake. This fault runs from
around town," says \u m e i Wang, Northern California to British Co
the Director of Earthquake Pro lumbia. “When we have a subduc
grams for the Oregon Department tion quake, it will be much worse
of Geology and Mineral Industries than anything we’ve seen in Or
(DOGANI). “Look at how the West egon,” warns Wang. “There could
Hills rise so dramatically from the be damage in three states and
nearly flat area along Highway 30. Canada, so it may take a while for
T hat’s a fault running essentially supplies to reach us.”
“In addition, we expect a tsu
through downtown Portland.
W
nami to hit the coast within a few
minutes of the earthquake.” A tsu
nami, or tidal wave, is actually a
series of waves over several hours
that can devastate coastal commu
nities. “If you go to the beach, you
need to know that you should head
up hill or inland as soon as you feel
an earthquake. Don’t wait for a warn-
ing siren,** she cautions.
Subduction zone earthquakes oc-
cur every 200 to 1,000 years. The
last one was in January 1700, s o ils
possible we’ll have another one soon.
It’s also possible that it won t hap
pen for 500 years.
All those potential earthquakes
keep Wang busy. She’s an ex-Cali
fornian with degrees in geology and
engineering who’s been in several
earth q u ak es and re
searched many more.
Her current project is to
let Oregonians know
what the risk from fu
ture earthquakes might be.
“We’ve taken information about
Oregon’s geology and put it together
with general information about
population and buildings and come
up with some estimates of what
could happen,” explains Wang. “If
we have a subduction zone earth
quake, our most current estimate is
that more than 5,000 people could
die, along with billions of dollars of
damage across the state.”
Most injuries and damage comes
from buildings that can’t withstand
the shaking of a quake. “Some of
the most dangerous buildings are
old brick buildings without any steel
reinforcement,” says Wang. “There
are 1,500 of these in Portland, and
in a major earthquake, many of them
would be heavily damaged or com
pletely destroyed.” Although old
buildings in Portland have already
withstood several small to moder
ate earthquakes, that s not neces
sarily a comfort. “Each time a build
ing goes through an earthquake, it
loses some of it’s ability to absorb
another shock. For example, the
Grays Harbor Courthouse was seri
ously damaged in the July 2 earth
quake, even though it had gone
through larger earthquakes before.
On the other hand, a typical house
made out of wood rarely collapses
in a quake, though it can still suffer
substantial damage."
Wang and co-worker, Lou Clark,
recently published a study detailing
Continued on next page
S ummer E vents
F latlan d s
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The Earthquake Hazards: Amplification of earthquake waves, liquefaction of soil,
and landslides triggered from shaking relate to the geologic settings of the valley,
near the river and in the hills.
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