The two earthquakes that many residents of Los Angeles felt over the Fourth of July weekend were not just a source of excitement, curiosity, or fear. They also triggered frustration.
Residents received no prior warning about these earthquakes through an alert app introduced earlier in the year, which had been marketed as the country's first early earthquake warning system. This led to some expressing their anger on social media towards the city and the mayor, even though officials stated that the app had performed as intended.
Although the 7.1 and 6.4 magnitude quakes caused significant damage near their epicenter, roughly 100 miles away in Ridgecrest, the shaking in Los Angeles did not reach the app's alert threshold.
Now, city officials are making adjustments to the Shake Alert LA app to provide the public with more information when milder quakes, like those experienced during the recent events, occur.
These changes have broader implications for the role of technology in earthquake situations, and it highlights the need for public input and experimentation in perfecting earthquake warning apps.
You had ONE job, Shake Alert LA pic.twitter.com/RAasBHaiWg
— Dominic Burgess (@dominicburgess) July 4, 2019
You had ONE job, Shake Alert LA pic.twitter.com/RAasBHaiWg
— Dominic Burgess (@dominicburgess) July 4, 2019
When discussing earthquakes, people often refer to their magnitude. However, magnitude alone may not provide the best understanding of how an earthquake affects a particular location.
Seismologists use an "intensity" metric to describe how an earthquake is perceived at a given place, considering factors like the distance from the epicenter, the type of seismic waves, and more. This is quantified using the Modified Mercalli Intensity Scale, which ranges from 1 (barely detectable) to 10 (severe). Shake Alert LA operates based on this scale.
When designing Shake Alert LA, the city and the U.S. Geological Survey (USGS) agreed to send alerts for earthquakes with an estimated intensity of 4 or higher.
"The policy decision we made is that we didn't want to alert people unless they would experience potentially damaging shaking," explained Robert de Groot, the national coordinator of outreach and education for Shake Alert at the USGS. "Level 4 is where that level of shaking begins. At level 3, it's just minor light shaking. It doesn't do much."
This policy played out during the recent earthquakes, as they were too distant to qualify as a 4 in Los Angeles and were classified as level 3 with light shaking, which led to no notification. As Shake Alert stated on Twitter, it "performed as designed."
"Shake Alert is about shaking, it's about how the ground moves," de Groot emphasized. "We are concerned about the shaking that a magnitude 7.1 earthquake produces and where that shaking occurs."
However, negative feedback has spurred changes.
So the app did nothing during today's quake and therefore 'performed as designed.' Seems like a pretty low bar to achieve.
— Kyle Krupinski (@KyleKrupinski) July 4, 2019
So the app did nothing during today's quake and therefore 'performed as designed.' Seems like a pretty low bar to achieve.
— Kyle Krupinski (@KyleKrupinski) July 4, 2019
Over the weekend, the USGS and city officials agreed that Shake Alert would begin notifying users for level 3 intensity earthquakes or higher.
"The general sentiment from the public is that they would like to be informed about any seismic activity, even if it's only minor shaking," de Groot added.
A month earlier, the USGS had made another adjustment to the app unrelated to recent quakes. Shake Alert now provides information for magnitude 4.5 or higher events, whereas the previous threshold was magnitude 5. This change will not significantly affect operations, as magnitude and intensity differ. Instead, the more substantial change is the new intensity adjustment. Lowering the intensity threshold alters the app's purpose from delivering notifications about potential danger to sending alerts for both minor shakes and major events.
"If people want that, they should have it," stated John Vidale, director of the Southern California Earthquake Center. "Knowing quickly when you've felt an earthquake is reassuring. Knowing that it's not a severe earthquake is as valuable as knowing when a major one is happening."
However, changing the notification threshold from 4 to 3 carries certain risks, such as an increased number of notifications due to the more frequent occurrence of low-intensity events. It could potentially lead to annoyance or desensitization to notifications for significant events as the app becomes associated with minor occurrences.
"It's a bit tricky because people don't always know what's most beneficial during a dangerous situation like an earthquake," Vidale acknowledged. "We don't want unintended consequences to negatively impact the system. However, the desire to be informed about moderate shaking seems reasonable."
As the first of its kind in the U.S., Shake Alert's public response may influence the design of similar systems across the country. The goal is to expand such systems along the West Coast. With input from the public, scientists, and policymakers, the role of technology in earthquake response remains a work in progress.
"It's bound to evolve significantly in the coming years," Vidale predicted. "The potential is clear, but timely alerts will be improved in various ways as more people contribute to its development."