Twice during her childhood, Jessica Gourley experienced historic earthquakes in California — the magnitude 6.9 Loma Prieta earthquake that shook the San Francisco Bay Area in 1989 and the magnitude 6.7 Northridge earthquake in 1994.

Gourley was 7 at the time of the Loma Prieta quake and remembers being cut by broken glass in the home of a family friend. Gourley, who grew up in Oregon, was 12 and on a family trip to Disneyland when the Northridge quake struck. She was on the top floor of a high-rise hotel and remembers the building swaying.

"My mom said twice, 'It's going to fall over. It's going to fall over,'" she said. The hotel withstood the earthquake, but Gourley was left with an appreciation of the Earth's power and how a seismic event can damage a city.

Her own earthquake experiences echo in her work as an emergency management analyst for the city of Eugene and as she and her colleagues prepare Eugene and Springfield for the potential of a much more massive temblor: a magnitude 9.0 Cascadia earthquake.

The two California earthquakes lasted seconds, said Gourley, now 36. The Cascadia earthquake might last as long as five minutes and will be hundreds of times stronger.

Earthquake experts say the Cascadia subduction zone, where one plate of the Earth's crust is sliding under another plate below the Pacific Ocean, is due for a major earthquake. Saturday was the 319th anniversary of a magnitude 9-plus earthquake along the Cascadia zone. The Jan. 26, 1700, temblor was a full rupture of the zone, splitting along the seam from northern California to southern British Columbia in Canada.

The huge earthquake unleashed a tsunami that slammed into Japan, where the event — and the date — was recorded. Earthquake experts, calculating how long it would take a wave to roll across the Pacific, say the earthquake happened around 9 p.m.

The city of Eugene and the University of Oregon held events Saturday to not only mark the date, but also to review the looming danger of the Cascadia earthquake and what people living in the southern Willamette Valley can do to prepare for it.

For Gourley and other local emergency management officials, the Cascadia earthquake is a constant thought. The Cascadia has been quiet for hundreds of years, but it could rumble again relatively soon.

"As times goes on there's more strain build up on the subduction zone," University of Oregon professor Doug Toomey has said.

There's a 10 to 20 percent chance of a magnitude 9 or greater earthquake along the Cascadia subduction zone in the next 50 years, said Toomey, a seismologist.

"We believe it will happen," said Ken Vogeney, emergency manager for the city of Springfield. "We just don't know when."

When it does happen the disaster will be unlike any wildfire, severe storm or other localized disaster Lane County residents have experienced. The earthquake will cause destruction in northern California, Oregon, Washington and parts of Canada, Gourley said. So help from neighboring communities — that cities such as Eugene and Springfield rely on — won't be there.

"This is going to be a regional issue," Gourley said.

State-produced maps detailing the expected severity of shaking show that Eugene and Springfield won't experience as strong as shaking as the surrounding area. But Vogeney said that shouldn't give residents a sense of security. The shaking will still be strong.

"(It will be) strong enough that you may get knocked off your feet," Vogeney said. "You may have difficulty standing. Things will fall. Structures will be damaged. Bridges will be damaged."

People living in the Eugene-Springfield area should prepare to be on their own for at least two weeks after the earthquake hits, said city of Eugene Emergency Manager Kevin Holman.

Damage to the two cities will be drastic, Holman and Vogeney said, with many residents left isolated. Toppled buildings in the downtown of each city and collapsed bridges on the Willamette River will add to the difficulty of navigating Eugene and Springfield after the Cascadia earthquake.

Holman and Vogeney warn that people should expect the electricity to be out, sewer lines broken and emergency services taxed. Food and gas also will be in short supply for an extended period.

"The word I use is chaos," Holman said. "It is going to be very chaotic."

Recovering from the Cascadia earthquake will take a long time. A week after the earthquake there will still be aftershocks, large magnitude quakes in their own right, Vogeney said. Given the scale of the expected disaster, it could take weeks and months for federal aid to reach the southern Willamette Valley.

"If there is any outside help getting to us it will be very minimal in a week," Vogeney said. "It might actually be noticeable in a month."

So, now is the time for city workers and residents to prepare.

Eugene and Springfield have a combined command center at Eugene Springfield Fire Station 6 on Willakenzie Road, next to Sheldon High School, ready for the Cascadia earthquake or another major disaster. Caches of water are stacked under desks. A closet holds dehydrated food to sustain 20 emergency workers for weeks.

How well prepared Eugene and Springfield are depends on how well individual residents prepare.

"Because of the catastrophic nature and the size and the scope of what we think is going to happen here (city governments) need to have some time to react," Holman said. "It's not realistic for us to stockpile a lot of supplies (for individuals) and things like that for financial reasons."

The Willamette River flows through Eugene and emergency managers have reviewed scenarios where an earthquake busts bridges and divides the city in two, potentially cutting people off from their homes and families.

The city of Eugene also has some high-tech equipment ready for the earthquake, including a mobile unit capable of linking cell phones and radios to satellites and drones — one equipped to allow visual inspection of the underside of bridges.

Local emergency managers used to ask people to be ready to go on their own for three days. But the Cascadia earthquake prompted city officials to join state emergency managers in asking Oregonians to be prepared to be self-sufficient for two weeks. Food and water top the list of necessities, Gourley said.

"You really are going to be on your own for a few weeks," Holman said.

People who have been in major quakes in California often tell local emergency managers that they feel ready for the Cascadia earthquake because they've been in earthquakes before. But Gourley said Cascadia will be so much bigger than even the historic earthquakes she experienced as a kid, and so Eugene and Springfield residents must do more now to prepare.

"Having our people prepared will decrease the time of recovery (from the Cascadia earthquake)," Gourley said.

Follow Dylan Darling on Twitter @DylanJDarling. Email dd@registerguard.com.