A minor earthquake that struck near Mount Hood on Saturday night triggered Oregon’s new ShakeAlert system for the first time. ShakeAlert is designed to give residents a momentary warning before a quake’s shock wave hits them.
Saturday’s quake, which measured magnitude 3.9, was too small to trigger regional emergency alert systems that are broadcast over TV, radio and to smartphones. So people didn’t receive warnings on their phones.
But the people who deployed the system were heartened that the ShakeAlert technology worked as designed Saturday.
“This is the first time that we have actually gone through this process in Oregon for an alert,” said U.S. Geological Survey scientist Robert de Groot. In a bigger quake, he said, alerts could have given people enough warning to get under a table or take other protective measures.
ShakeAlert operates in Oregon, California and Washington. California was first, in 2019; Oregon’s system went live in March, and Washington’s has been active since May.
The technology uses a network of regional sensors to detect an earthquake, then rapidly calculate a quake’s size and location, and where it is likely to generate shaking. ShakeAlert immediately sends alerts to phones and to other public safety networks within those areas.
Saturday’s quake hit about four miles northeast of Government Camp at 8:50 p.m. The staff at Charlie’s Mountain View restaurant reported feeling a gentle shaking, but didn’t immediately realize it was an earthquake. Even though the quake was small, de Groot said people reported feeling it as far away as Beaverton.
Initial calculations had indicated Saturday’s quake was a 4.0, just large enough to trigger emergency alerts in some automated safety systems close by. Those automated systems may slow trains or shut off gas valves. Larger quakes trigger wide alerts.
A 5.0 quake, which is 30 times more intense than Saturday’s, would produce alerts over the Wireless Emergency Alerts (WEA) system. WEA warnings reach every smartphone in areas close enough to feel significant impacts, unless the phone’s owner has disabled public safety emergency notifications.
“If it was a magnitude 5, that’s when alerts would be delivered,” de Groot said. “And it would be delivered to people who would feel a minimum level of shaking, which is considered to be a light level of shaking.”
That could reach a wide geographic range.
Because an earthquake’s vibrations move more slowly through the earth than radio signals travel over wireless networks, it’s possible to provide a warning that ranges from a couple seconds to a very significant advance notice.
Warnings about Saturday’s quake, for example, gave Hood River 1.9 seconds of warning, according to ShakeAlert metrics. However, de Groot cautioned that may overstate the amount of warning people actually had – he said it takes some period of time for ShakeAlert to process information before sending out the alerts.
Farther away, the warnings arrived long before any shaking. In Portland, 49 miles from Saturday’s epicenter, the alert provided 11.9 seconds of warning. In Eugene, 112 miles away, ShakeAlert gave 40.5 seconds of warning.
Saturday’s quake wasn’t large enough to trigger smartphone notifications. People who have smartphone apps that tap into the ShakeAlert network can customize their notifications to receive alerts at modest thresholds, for quakes of magnitude 4.5 or greater.
In Oregon, de Groot said there are two such apps available – MyShake and QuakeAlertUSA. Additionally, smartphones running Google’s Android operating system have ShakeAlert notifications built in. (Again, though, you don’t need these apps for notifications about larger quakes – the WEA system should notify smartphone owners automatically.)
The apps will provide additional information about a quake’s size, epicenter and intensity – but de Groot cautions that you should take protective measures before studying the data too closely.
“You can look at your phone while under the table,” he said, “but get under the table.”
