By Fred Leeson
A major earthquake in Portland could raise havoc with the
network of bridges knitting the city's east and west sides.
Only two of 10 bridges spanning the Willamette River
the Marquam and portions of the Burnside have been
fitted with the easiest and cheapest seismic bracing.
State and county engineers have identified deficiencies that
could prove crippling in a major earthquake. But so far, there
is no timetable or budget for modifications that would run
into tens of millions of dollars.
"I think the risk is great," said Franz Rad, a
Portland State University civil engineering professor who
has spent a decade studying potential earthquake impacts on
buildings in the Portland region.
Although his work focuses on buildings, Rad has been concerned
enough about bridges to discuss seismic bracing with the Oregon
Department of Transportation as the state launches a major
bridge repair program. "I think we are not moving fast
enough," Rad said.
Improving the bridges involves the complex interplay of money,
geology and antiquated bridge designs. "The problems
are huge," said Sharon Wood Wortman, a Portland bridge
historian and author who has paid close attention to earthquake
Wortman said the nature of soil in the heart of Portland,
laid down over centuries by the Willamette River, is a key
danger. "Essentially, we have very large bridges sitting
on an alluvial bog," she said.
Five of the city's 10 bridges are owned and maintained by
Multnomah County: the Sellwood, Hawthorne, Morrison, Burnside
and Broadway. "All our bridges were designed before seismic
was an issue," said Ian Cannon, Multnomah County's engineering
As a result, he said it is difficult to estimate how powerful
a jolt they could survive.
The picture is similar with four state-owned bridges. No
seismic retrofits have been applied to the Fremont, Ross Island
or St. Johns bridges. Nor is there any earthquake bracing
on the Steel Bridge, which is owned by Union Pacific Railroad
and is the only east-west line for Portland's growing light-rail
Whether a major quake will occur in Portland seems to be
a question of when, not if. But scientists cannot predict
the timing or severity of earthquakes. "It could be tomorrow,"
The city's newest river crossing, the Fremont Bridge completed
in 1973, has a span that is expected to survive a major quake,
but the bridge approaches at both ends are considered vulnerable.
State and county officials have approved improvements ranging
from $12.5 million to $33 million each in recent years for
the Ross Island, Hawthorne, Broadway and St. Johns bridges.
But none of that work involves earthquake strengthening.
Cannon said the first priority is keeping the bridges functional
for users ranging from heavier trucks to more pedestrians
"California has a different philosophy," he added.
"Seismic is an imminent risk. Oregon doesn't see the
problem the same way."
California got the message in 1971 and again in 1989 after
quakes in the San Fernando Valley and the San Francisco vicinity,
respectively, severely damaged freeway bridges and overpasses.
The 1989 quake persuaded the Oregon Transportation Department
to apply "phase one" bracing techniques to the Marquam
Phase one improvements tie bridge decks to vertical supports
to keep decks from falling and protect the lives of people
on bridges when a quake occurs. But damage to columns could
still render a bridge useless. More expensive phase two repairs
not yet applied to any Portland bridges add
bracing to bridge piers under water.
The Oregon Legislature last year passed a $2.46 billion statewide
transportation package that includes $1.6 billion to repair
But it appears that only a small portion of that money will
be used for earthquake bracing. That's because earthquake
protection is required for new bridges, but not for the repair
of existing structures.
State transportation officials still are deciding which bridges
to repair and which to replace. "The money will fix some
seismically challenged bridges," said Dave Thompson,
a Transportation Department spokesman. "But it's a lucky
side effect, not the main issue."
Rad, the civil engineering professor, said the state is "looking
more at maintenance and crack control. They're not really
worrying about earthquakes."
The state funding package also includes $361 million to be
allocated to city and county bridges. Multnomah County hopes
to tap that fund to complete a $30 million Sauvie Island Bridge
replacement. That bridge also is considered highly vulnerable
County Commissioner Maria Rojo de Steffey, who has been lobbying
for the Sauvie Island project, also hopes some state money
will be available for replacing the Sellwood Bridge, a lightly
built structure that suffers from cracking prompted by shifting
earth at its west end.
"The cost for seismic work is just exorbitant,"
Rojo de Steffey said. "Unfortunately, the funding is
really hard to find. The issue is really about funding."
James Roddey, community education coordinator for the Oregon
Department of Geology, said Portland is vulnerable to comparatively
shallow crustal earthquakes, as well as to much stronger quakes
from the Cascadia subduction zone that runs for about 800
miles off the Pacific Northwest coast.
Roddey said Portland has experienced a few crustal earthquakes
of magnitude 5.5 in the past 50 years without suffering bridge
damage. Cannon said some of the older bridges, such as the
Steel, Broadway and Hawthorne, appear to have been more sturdily
built because they originally carried heavy streetcar traffic.
But a subduction quake could prove far more severe than any
recent quakes, perhaps hitting magnitude 8 or 9. On the logarithmic
severity scale, each full number represents a-tenfold increase
in earthquake strength.
A magnitude 7.2 subduction quake hit Kobe, Japan, in 1995,
killing 5,400 people, leaving 235,000 homeless and creating
losses estimated at $95 billion to $150 billion. Like Portland,
much of Kobe was built on alluvial soils.
"We will get one of those in Oregon sooner or later,"
said Rad, the PSU engineer.
The most recent subduction earthquake in the Portland region
is believed to have occurred in 1700. But the same type of
quake rocked the Alaska coast as recently as 1964.