A catastrophic earthquake in Oregon could leave the Medford area economically isolated under a scenario that describes months or years of effort to rebuild Interstate 5.
In planning for "the big one," the Oregon Department of Transportation has identified Highway 97 through Klamath Falls rather than I-5 as the "seismic lifeline" route through the southern portion of the state. That means repair efforts would first be focused east of the Cascade Mountains instead of on I-5.
Scientists say the ocean floor offshore Oregon — referred to as the Cascadia Subduction Zone — is subject to major shifts about every 500 years, producing magnitude-9.0 quakes. That's the same magnitude as Japan's devastating March 2011 earthquake.
An Oregon State University research report also suggests that the southern end of the fault — a portion that skirts approximately the southern third of the Oregon Coast — slips far more frequently, producing earthquakes in the lower magnitude-8s about every 240 years.
In comparison, the Loma Prieta earthquake in the San Francisco Bay Area in 1989 was a magnitude-6.9 quake. An 8.0-magnitude quake would be more than 10 times as powerful.
Under a seismic report prepared by the Oregon Department of Transportation, repairing I-5 quickly after a major earthquake would be difficult because of the large number of bridges it passes over, including the viaduct through Medford. Instead, ODOT would focus on Highway 97 and then link back to I-5 via Highway 58, which leads to Eugene.
The ODOT scenario has troubled local officials, prompting them to seek a long-term solution to avoid economic chaos for the region.
"Cost is no object for the Columbia River Crossing, but it appears to be for the Interstate 5 West Coast corridor," said Medford Councilor Al Densmore, referring to a proposed I-5 bridge over the Columbia. "From an emergency perspective, we know we will be on our own for a while."
In its seismic lifeline scenario, ODOT is planning for the worst, identifying a route in Oregon that would allow north-south freight traffic to continue to roll through the state.
If the big one strikes, the easiest route to get back up and running is Highway 97 through Klamath Falls and Bend, ODOT officials say. The route has fewer bridges and runs through relatively flat terrain.
ODOT plans to release a report in the next few weeks that recommends investing in the Highway 97 corridor to create a link through the state that could weather a powerful earthquake.
Under the ODOT scenario, bridges in Western Oregon would sustain serious damage or be destroyed, and dozens of landslides are expected to block roads.
U.S. Highway 101 on the coast would have bridge failures and would be largely impassible. Existing highways connecting Highway 101 to I-5 would be impassable because of bridge failures, landslides, fallen trees and washouts.
ODOT projects damage to the state's highway system would result in an economic loss of $350 billion over an eight to 10-year period.
ODOT prepared a March 14 letter to legislative committees on emergency preparedness to explain the potential impacts. The letter describes how California and Washington have made big investments in bridges to avoid the kind of catastrophic destruction to their road systems.
Under the ODOT proposal, which will be the subject of a full report in a few weeks, the primary route through the state after a quake would be Highway 97. In addition to the Highway 58 connection to Eugene, it would connect to Portland via Interstate 84, which runs through the Columbia Gorge.
So-called second-tier routes through the state would be Interstate 5 south of Eugene and highways 38, 22 and 30 to the coast.
Gary Leaming, spokesman for ODOT, said ODOT has attempted to identify the most cost-effective routes to move traffic through the state as it attempts to prepare for a major quake.
He said the hardest-hit area from a major quake likely would be Southern Oregon, especially areas along U.S. 101 south of Coos Bay. He said that coastal area would be particularly isolated by a big quake.
"It will be so catastrophic," Leaming said. "We'll be hard-pressed to get goods and services into that area for a while. It will be a regionwide crisis."
Services such as water, sewer, gas and electricity could all be disrupted. Because the roads would be knocked out, gasoline would be in short supply in Southern Oregon.
The I-5 viaduct through Medford has been improved in recent years, but may suffer so much damage that it couldn't be used after a significant quake, Leaming said. Even if the viaduct managed to survive, there are so many other bridges in Southern Oregon that could crumble along the interstate, he said.
Transportation will be the key to bringing in supplies, so ODOT is trying to identify potential routes that could be improved at a reasonable cost to keep freight moving through the state, he said.
Densmore said the ODOT report has raised concerns among local officials who want to discuss some kind of emergency preparedness in case the interstate is shut down and Medford is isolated from the rest of the state.
He said the city has been preparing more for disasters in recent years, and he expects more planning in the future.
Densmore said there has been some discussion about turning North Phoenix and Foothill roads into an alternative route in the event I-5 is shut down through Medford.
The city would like to enter into discussions with the state about improving the viaduct or finding a replacement route around the city in the future, he said.
"We don't know what the answer is," he said. "It's time to start this planning process."
Reach reporter Damian Mann at 541-776-4476, or email email@example.com.