While no major damage was reported Tuesday night in the Santa Clarita Valley from the magnitude-5.2 earthquake that hit the unincorporated area of Mettler, California, 60 miles northwest of the city, it was felt by many.
That seemed to become apparent a little faster than usual this time around.
Thanks to the U.S. Geological Survey data and ShakeAlert program, social media was flooded with posts by those who received a heads-up before the earthquake even happened.
While the ShakeAlert program isn’t new, a relatively quiet period for earthquakes combined with a recently lowered threshold for alerts meant more people might start to notice the alerts, according to experts.
USGS seismologist Robert DeGroot said someone’s location could impact whether they received an alert and how early the alert came before shaking was felt.
Some reported hearing the loud Amber Alert-style alarm go off on their digital devices up to 10 seconds before a major earthquake, he said, which is the idea — while some reported getting an alert after the main event.
Renowned seismologist Lucy Jones, who worked on the creation of the ShakeAlert program, said the threshold for when people get an alert was lowered after the Ridgecrest earthquake almost five years ago, about two hours east of Mettler.
When the Ridgecrest quake hit, Jones said in an interview with The Signal on Wednesday, many didn’t receive the alert because the intensity had to be a level 4 for when the USGS would release its data to the notification apps.
The situation made many question the efficacy of the app, Jones said, which led to further study, discussion and a lower threshold.
“So, the decision has to be made — ‘Where do you do it?’” she said, referring to when people should be notified, “given that this level of shaking some people feel strongly and some people don’t notice.”
The intensity scale is a 1-to-10 scale, she said, and 10 represents severe damage and 1 is not really felt at all.
DeGroot said under the current system, most people received an alert if their cellphones were in an area where the seismic activity was forecast at level 3 intensity — a scale separate from magnitude that focuses on how the activity is felt as opposed to its measurement. He likened a 3 to the rumbling feeling one might experience on the first floor of a home if a very large truck drove past.
To put it to scale for the Mettler earthquake, the highest recorded intensity from Tuesday’s earthquake was an intensity of 7, closer to the epicenter, Jones said.
In Santa Clarita, the intensity levels registered at a 4 on most of the readings, she said, which is why so many people probably received alerts.
How it works
USGS officials on Wednesday made it clear that they do not issue any of the actual alerts, but they do collect the data for the apps that do, like MyShake, as well as the automated emergency alerts that iPhones and most Android phones have, DeGroot said.
“The USGS puts out a signal and leaves it up to other developers to create a phone app or have some way of delivering it to people,” Jones said, who added that while she worked on the app’s development, she’s no longer a part of the program.
DeGroot said cellular service providers manage their own proprietary means for how the information is delivered to the phone, with most having opt-out options for those who don’t want to receive the alerts.
The early numbers indicated that about 500,000 people received the alerts during Tuesday’s shakeup in Mettler.
“There were a lot of folks that felt the earthquake, that also got alerts on their phones, and also many that spoke to the fact that there was a lot of time inbetween when they got the alert and when they felt shaking,” DeGroot said.
But there are always wrinkles to work out after an incident, too, he said.
“And some people were saying, ‘Well, my wife got an alert on her phone, but I didn’t get an alert on my phone,’” DeGroot said, “and so we’re always trying to troubleshoot those sort of issues around different phones, and it’s a whole bunch of factors.”
He added that there’s an opt-out ability for Android phone users, and for iPhone users, in their notifications settings, scrolling to the bottom shows “government alerts,” and he recommended for those who want to be in the know on alerts to select “emergency alerts,” and turn on “local awareness,” which is supposed to improve a phone’s ability to register alerts from notifications.
Evolving alerts
Developed about 12 years ago, the ShakeAlert program’s engagement and widespread usage have been a process.
So many factors go into the release of the data and the process behind it, said Jones, adding that data scientists benefited from the analysis provided by social scientists with respect to how the numbers can be utilized and shared.
“I do know that one of the big issues is, ‘When do you send an alert?’” she said, referring to the discussion that took place in response to Ridgecrest.
“And so, there was this decision made, and this was true at the time of the Ridgecrest earthquake, to not warn, because it wasn’t going to be dangerous shaking in LA — but of course, everybody in L.A. felt it, and nobody got a warning,” she added. The backlash is part of what prompted the change.
And there is some degree of subjectivity when people talk about the alerts and what they’re feeling, Jones said.
“Earthquakes put out shaking at a wide range of frequencies,” she said. “High frequencies die off more quickly than low frequencies — so when you’re farther away, it’s a rolling motion, when you’re nearby, it’s a jerking motion.”
A phone’s location can impact the timeliness of when a phone receives an alert, she added, and a person who’s on the third floor of a well-constructed building is going to feel it less than someone on the first floor due to how seismic energy moves.
As the area’s seismic activity increases, which is expected because the last decade or so has been relatively quiet, Jones said, technology that helps with future warnings could play an important role in saving lives.
“We’re trying to develop trust in this application,” Jones said, “so when we really do need it, people will have seen it before, be a little bit more alert, know what to do with it.”
