Coastal towns would be inundated. Schools, buildings and bridges would collapse, and economic damage could hit $32 billion.
The chilling report by the Oregon Seismic Safety Policy Advisory Commission was presented Thursday to Oregon legislators.
In 2011, the Legislature authorized the study of what would happen if a quake and tsunami such as the one that devastated Japan hit the Pacific Northwest.
The Cascadia Subduction Zone, just off the regional coastline, produced a megaquake in the year 1700. Seismic experts say another monster quake and tsunami are overdue.
"This earthquake will hit us again," Kent Yu, an engineer and chair of the commission, told legislators. "It's just a matter of how soon."
When it hits, the report says, there will be devastation and death from Northern California to British Columbia.
Many Oregon communities will be left without water, power, heat and telephone service. Gasoline supplies will be disrupted.
The 2011 Japan quake and tsunami were a wake-up call for the Pacific Northwest. Governments have been taking a closer look at whether the region is prepared for something similar and discovering it is not.
Oregon legislators requested the study so they could better inform themselves about what needs to be done to prepare and recover from such a giant natural disaster.
The report says that geologically, Oregon and Japan are mirror images. Despite the devastation in Japan, that country was more prepared than Oregon because it had spent billions on technology to reduce the damage, the report says.
Jay Wilson, who works for the Clackamas County emergency management department and is vice chair of the commission, visited Japan and said he was profoundly affected as he walked through villages ravaged by the tsunami.
"It was just as if these communities were ghost towns and for the most part there was nothing left," he said.
Wilson told legislators that there was a similar event 313 years ago in the Pacific Northwest, and "we're well within the window for it to happen again"