Much of downtown Medford could become a pile of rubble if a massive Cascadia subduction zone earthquake unleashes its fury on Southern Oregon.

Historic Main Street, where it intersects with Central and Riverside avenues, would shake for up to five minutes, releasing the energy equivalent of multiple hydrogen bombs from two tectonic plates grinding and slipping along a 600-mile stretch in the Pacific Ocean.

City officials have identified 192 buildings in or near the downtown that are constructed of unreinforced masonry, which means facades could fall on sidewalks and roadways, or the building could just collapse entirely if it hasn’t been seismically retrofitted.

The danger from these downtown buildings is just the beginning. The valley likely would see blocked roads, no power, no running water, failed sewer systems and largely be cut off from the rest of the world. Nearby Jacksonville also has a downtown filled with historic buildings, which likely would collapse, endangering people both inside and outside as debris rains down on the street.

The last time the 600-mile-long Cascadia subduction zone unleashed its power was on Jan. 26, 1700, and experts say that according to the historical record, we’re about due for another one.

Scientists have been monitoring the subduction zone for more than 20 years, and they know it’s active, but whether it’s going to release tomorrow or decades from now is open for debate.

“There’s a bomb with a fuse on it, but we don’t know how long the fuse is,” said Chris Goldfinger, a leading seismology and subduction zone expert at Oregon State University.

The subduction zone is an area where the North American plate and the Pacific plate collide, moving a few inches each year in opposite directions. The Pacific plate is moving to the northwest, and the North American plate is moving southwest.

An earthquake there could release 10 times the energy of the Loma Prieta quake that rocked the Bay Area in 1989, killing 63 people, injuring more than 3,000 and causing an estimated $7.4 billion in direct damage. The power of a subduction zone quake may register a magnitude 9 near the epicenter at the coast and possibly an 8 by the time it reaches the valley.

The destructive force of this impending quake has come into focus for geologists and for emergency service providers, who are ratcheting up plans to alert the public to be prepared for an unprecedented disaster.

From 9 a.m. to 5 p.m. Sept. 26 and 27, local and state officials will talk about the subduction zone quake during a Southern Cascadia Earthquake Symposium at the Asante Smullin Education Center, 2825 E. Barnett Road. If you're interested in a less technical presentation for the general public that will be held from 7 to 8:30 p.m. at the same location on Sept. 26, go to http://www.redcross.org/news/event/local/oregon/Prepare-Out-Loud-Medford.

Chris Goldfinger, a geology professor at Oregon State University who will be one of the speakers at the event, said the good news for Medford area residents is that they will have about one minute of less intense shaking before the real force of the quake is felt.

This one minute should give most people the time to either dive under a desk in a building designed to withstand a quake or allow people to leave an unreinforced masonry building and find a spot where no debris might fall down.

Because the Rogue Valley is so far from the epicenter, the sharp, jackhammer motions shouldn’t as much of a problem here.

Goldfinger said his mother lived in the Bay Area when the Loma Prieta quake hit.

“My mom lived at the epicenter,” he said. “She was at the sink doing dishes near a 500-pound woodstove. The next thing, she and the woodstove were in the living room and the shelves rolled over.”

His mother didn’t suffer any major injuries.

Goldfinger said the subduction zone quake shouldn’t knock you off your feet as much as the one his mom experienced.

“It will not take you by surprise,” he said. “You’ll have a little bit of time to decide what to do.”

In downtown Medford, he said people should be aware that they need to find a safe place that isn’t near any structures that might collapse, or where chunks of masonry could fall off.

“You should have in mind a response plan,” he said.

Many local residents might wonder what to expect if a subduction zone quake hit off the coast of Oregon.

Goldfinger actually rode out a subduction zone quake in Tohoku, Japan, in 2011, and he said the movement such a quake generates is predictable but still devastating.

For the first minute, it will send out smaller intensity pressure waves, or p-waves, which should make it somewhat easier for many residents to find a safe place to ride out the four-minute roller coaster of shear waves, or s-waves.

The s-waves are the part of the quake that causes the most damage.

In Goldfinger’s office in Corvallis, it is unreinforced masonry, and he plans to walk out of the building to a spot that’s safe.

“We’ve got 100 people in the office, and we should all be able to get out in a minute,” he said.

While there is plenty of generic advice on what to do if an earthquake strikes, Goldfinger said you need to quickly size up your situation and determine whether you need to evacuate a building or just dive under a desk for cover.

Many Medford area residents likely are not prepared for an earthquake, but Marino Rossi is. He works in an unreinforced masonry building that also houses Howiee’s on Front restaurant and bar.

He’s got two weeks' worth of water and food at home as well as other provisions, such as multiple propane tanks for cooking, and he’s prepared to exit his office building or take more extreme steps to flee to safety.

“If everything is crumbling, I’d probably go out the window into Howiee’s patio,” he said.

Rossi is also a broker at Henselman Realty and Management LLC, which specializes in leasing downtown buildings, many of which are made out of unreinforced masonry. Some of the buildings he handles, including the Sparta at the corner of Main Street and Riverside, have been retrofitted with steel bracing and other improvements to keep it standing in a quake so people can safely leave the building.

City Hall also has been reinforced seismically, but only to the extent that it will stay standing so that workers can get out of the building. City officials don't expect the building to be so damaged by a Cascadia quake that it would have to be rebuilt.

The Medford City Council recently expressed an interest in getting grants to help stabilize downtown buildings so they are safer, an expensive proposition.

Rossi said many of the owners he represents are concerned about tenant safety and have expressed interest in applying for the grants through the city.

When the shaking stops, the disaster is far from over.

Water and food supplies might be limited, so experts recommend having at least two weeks' worth on hand.

Larry Masterman, emergency management coordinator for Medford, said when Japan had its subduction zone quake, it was better prepared than most countries.

“Even as robust as Japan standards are, they got clobbered,” he said.

In Japan, 22,000 people lost their lives and 300,000 buildings were destroyed. Six years later, critical buildings such as hospitals are just being completed and 30 percent of the residents who were displaced still live in temporary housing.

In this valley, residents should be prepared to go weeks or months without power, and cellphones may work only as long as emergency generators keep running.

As a result, Masterman suggested residents devise a plan for family members to meet at a designated place after a quake.

If markets reopen, expect residents to deplete shelves quickly. Also, because internet service might be knocked out, many stores likely would take only cash. Residents who need medications could find their supplies cut off.

With so many services in jeopardy, the state is developing various resilience plans, anticipating coastal areas could be isolated for 12 to 18 months. Medford’s only link to the outside world might be the airport, if it’s still operational, which could limit the amount of supplies being brought in for an area with a population of about 200,000. Coastal areas might receive shipments only via the sea because roads could be impassable.

Masterman said east and west Medford could see the viaduct and bridges over Bear Creek collapse. Since the hospitals are on the east side, that will be a problem for west Medford residents. Driving around town might be difficult, so bikes may become one of the best temporary ways to get around.

“Cargo bikes are going to be gold, or bikes with trailers,” he said.

Masterman suggested residents obtain a filter used by hikers and back-country campers that can make various sources of water fit for human consumption. In a pinch, residents can run creek water through a coffee filter and add a bit of chlorine bleach and let it sit for a while to kill off bacteria. When you drink the water, it should have a slight taste of chlorine.

During the Loma Prieta quake, power was disrupted for three days, said Masterman, who worked in the Bay Area at the time. There was no water for firefighters, buildings swayed like dancers and the power plant wouldn’t start up. Buildings crumbled, and power poles and trees fell over. Two sections of the Cypress freeway and a portion of the Bay Bridge collapsed in Oakland, and in San Francisco, the upper decks of the Central and the Embarcadero freeways collapsed.

For the Medford area, a subduction zone quake could result in even more damage.

“Imagine 10 times that magnitude in a place with less resources,” Masterman said. “It’s going to be a scary time.” 

— Reach reporter Damian Mann at 541-776-4476 or dmann@mailtribune.com. Follow him on www.twitter.com/reporterdm.

Medford Earthquake Map

 

 

Cascadia Subduction Zone