Why cellphones in Anchorage keep getting emergency tsunami alerts when there’s no danger after faraway quakes

Some cellphones in Anchorage beeped and vibrated with an emergency tsunami warning Monday afternoon.

“You are in danger. Get away from coastal waters. Move to high ground or inland now,” the alert said.

But there was no danger in Anchorage, which was more than 500 miles from the site where a magnitude 7.6 earthquake shook communities along the Alaska Peninsula coastline and subsequently triggered a tsunami wave.

The alert was intended only to reach communities within the tsunami warning zone, which stretched more than 500 miles from the Kennedy Entrance, 40 miles southwest of Homer, to Unimak Pass, 80 miles northeast of Unalaska, said tsunami warning coordinator Dave Snider. But somewhere in the chain of the emergency alert system, Snider said, overlapping boundaries caused alerts to show up on some Anchorage phones.

It wasn’t the first time this scenario played out in Anchorage after a big earthquake occurred hundreds of miles away, with no tsunami threat to the city. But the alert system that pushes emergency notifications to smartphones is complicated, said Jeremy Zidek, a public information officer with the Alaska Division of Homeland Security and Emergency Management.

The warning is first generated by the National Weather Service and then passed on to FEMA’s Integrated Public Alert and Warning System platform, which then works to pass the information to cellphone providers. Notifications are generated based on location, so the cell providers will ping users within a certain boundary or area from a specific cellphone tower.

“Basically, the wireless alert zones don’t necessarily match with the weather service alert zones, which don’t match with state and federal alert zones,” Snider said. “And when you mash it all together, especially in that one spot, you get alerts going to many more people than are intended.”

GCI customers who were in South Anchorage or even along the Turnagain Arm toward Girdwood likely received the emergency alert because the company has a cellphone tower near Anchorage that reaches customers along the Kenai Peninsula, GCI spokeswoman Heather Handyside said. Since the alert was intended to reach people on the Kenai Peninsula — the Homer area was part of the tsunami warning zone — any phones connecting to that cellphone tower would have received the warning.

Some people throughout Anchorage were similarly alerted of a tsunami warning in July, after a magnitude 7.8 earthquake in the same part of the Alaska Peninsula. (Monday’s earthquake was an aftershock of the July quake.) Snider said this is a known problem and the weather service is working with other agencies and systems to find a solution, but the different layers of the transmission system make it challenging.

An additional challenge lies in the vast remote areas of Alaska because some of the zones are much larger than they would be in more densely populated areas, like many states in the Lower 48.

“Tsunamis don’t happen often enough, like winter weather, for us to practice and rehearse and know what we’re dealing with — like when we get our snow tires on,” Snider said. “It’s tricky stuff and it’s a constantly evolving process, and we are certainly trying to get it right for everybody with the main mission of keeping everybody safe the first time.”

Zidek said that it’s better to warn too many people rather than too few.

“There may have been people in the tsunami area that were serviced by some of those towers that needed to receive that message,” he said.

He noted that it’s important for people to know the risks that are possible within their communities. Cook Inlet is deep and narrow, making it nearly impossible for a tsunami to hit Anchorage. Zidek said that people along the coastline, however, should be aware of tsunami danger and other threats that could arise from living so close to the ocean.

Immediately after the 7.6 earthquake Monday afternoon, aftershocks began to rumble through the region, causing additional temblors but not amplifying any tsunami risk. By Wednesday morning, there were more than 50 aftershocks recorded in the area, some as big as magnitude 5.7, according to the Alaska Earthquake Center.

Since the original magnitude 7.8 quake in July, there have been more than 400 aftershocks of magnitude 3 or higher, with 30 being bigger than magnitude 5, which are strong enough to cause damage, according to the U.S. Geological Survey.

A tsunami did form after Monday’s earthquake, but it wasn’t large enough to cause any damage. The highest wave was 2.3 feet above the tide, according to the National Tsunami Warning Center. Communities along the coastline evacuated to higher ground as they waited to see how severe the tsunami wave would be.

Earthquakes in that region of the Alaska Peninsula are common, according to a tectonic summary from USGS. In the last 120 years, eight quakes larger than magnitude 7 have occurred within 155 miles of Monday’s quake.

Snider said officials are still investigating how to improve the emergency alert notifications so that next time, they’ll only be received by people who are actually in danger.