As Southern California recovers from two massive earthquakes, a magnitude 6.4 on July 4, and a 7.1 the following day, Oregonians are likely wondering when the Pacific Northwest will get its next big shake and what, if anything, they can do about it.

There are, of course, lots of ways to prepare for "The Big One.” Emergency kits can be prepped and stored away. Hot water tanks can be bolted down. Evacuation plans and meeting points can be arranged among family members. But what if your phone or computer could let you know that strong tremors were about to occur? What if you had 15 seconds or a minute or more to prepare.

Seismologists around the region are hoping that becomes reality soon with the full implementation of the ShakeAlert earthquake early warning system in the Pacific Northwest. But there are still a number of hurdles to clear before you can expect to see an alert for an impending earthquake on your phone, said Leland O’Driscoll, ShakeAlert project manager who works out of the University of Oregon.

“ShakeAlert is live and functional from Canada to the Mexican border,” O’Driscoll said. “We’re getting alerts today, but it’s not publicly available everywhere.”

We need more sensors, he said, and the money to pay for them.

An early warning, not a prediction

The Pacific Northwest is a hotbed of geologic activity. Volcanoes along the Cascade Range poke up like the vertebrae of the regions spinal column, most of them sitting dormant, for now at least. The Earth’s crust ceaselessly shifts, cracks and crumbles as one tectonic plate slides under another along the Cascadia Subduction Zone, which runs the length of Oregon, just off the coast from Northern California north to British Columbia.

That a massive earthquake will strike somewhere along the subduction zone is a given, but quakes elsewhere serve as a reminder that — maybe tomorrow, or maybe in 50 years — the Pacific Northwest is going to experience a seismic event that will be life-changing for millions of people.

Earthquakes happen when a fault in the earth’s crust slips and the land on either side of the fault moves relative to one another. The shaking is the result of waves of energy radiating out from the spot on the fault line where the rupture occurs.

Two types of energy travel outward from the epicenter: primary waves, or p-waves, and secondary waves, or s-waves. The p-waves travel faster and usually don't cause much shaking or destruction. Using those initial p-waves, sensors can detect the strength of a quake, relay the message to an earthquake alert center and create a warning, allowing seconds or even minutes for people to prepare before the stronger s-waves arrive.

Courtesy/University of Oregon

Depending on the intensity of the quake and the distance, that window of warning could allow transit agencies to stop or slow trains, for hospitals to fire up generators or for normal folks to find a place to take cover. O’Driscoll said that, if the Cascadia Subduction Zone were to rupture from its southern end, Portland could have more than two minutes to prepare.

Officials are still working out exactly when to send the alerts. Shaking caused by earthquakes is measured on something called the Modified Mercalli Intensity Scale, which goes from 1 to 10. In Los Angeles, neither of the recent earthquakes met the threshold for an alert and none was sent. That left some in the region wondering why and officials said they would look at modifying the criteria to lower the threshold.

O’Driscoll said all of that would inform how and when officials send an alert in the Pacific Northwest.

“People would rather have a warning without shaking than shaking without warning,” he said.

Where to put that threshold is a delicate balance, said Robert de Groot, of the U.S. Geological Survey.

"Imagine getting 10 ShakeAlerts on your phone for really small earthquakes that may not affect you," he told the Associated Press. "If people get saturated with these messages it's going to make people not care as much."

Close, but not quite there

To have a fully functional system, O’Driscoll said, Oregon needs to have 75 percent of the 238 state-wide sensors in place. By August, that number should be up 125, 59 percent, with more coming next year.

The ShakeAlert program gets most of its funding from the U.S Geological Survey in the form of federal grants, but O’Driscoll and other officials with the program were hopeful that the state would chip in. A bill introduced in the Oregon House would have provided enough money for the system to be fully operational by 2023.

The funding specific to the ShakeAlert program was stripped out in a late round of negotiations and ShakeAlert was left to rely on federal grant money, a disappointing development, O’Driscoll said.

That money would have not only funded the sensors themselves, but would have also allowed for systems to deliver warnings to the public. In Los Angeles, residents can download an app called ShakeAlert LA that will deliver warnings to their phones. A similar app is set to roll out in the Bay Area in the fall and that type of technology can be repurposed for any region, including Oregon.

Some institutional entities in Oregon — public transportation agencies, school districts and universities — already have the infrastructure in place to receive early warnings. They just need a fully operational system in place to deliver them.

Despite the lack of state funds in the most recent budget cycle, O’Driscoll said the work he and his colleagues put in trying to lobby lawmakers would not go to waste.

“We put in a ton of effort to get ready and responsibly spend the funds,” he said. O’Driscoll plans to bring the matter back before lawmakers in the next session.

-- Kale Williams

kwilliams@oregonian.com

503-294-4048

@sfkale

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