Overreaching tsunami warning dropped for upper Cook Inlet

Jul 21, 2020

Credit NOAA

A magnitude-7.8 earthquake activated the national Tsunami Warning System late Tuesday night. The epicenter was 8 miles deep, south of Perryville and Chignik on the Alaska Peninsula. It was initially estimated at magnitude 7.4 but was revised upward.

The U.S. Tsunami Warning System activated about five minutes later, issuing an alert across coastal Alaska, from Seward to Unalaska, sending text messages to cellphones and triggering tsunami warning sirens in Kodiak, on the Alaska Peninsula and Aleutian Islands, as well as in Homer and Seward. 

Mike West, a seismologist and director of the Alaska Earthquake Center, said this type of earthquake is the kind they worry about for tsunamis. 

“It is the style of earthquake which tends to generate tsunamis,” West said. “All early signs indicate that this is on what we refer to as the subduction zone. It’s the interface, the plate boundary between where the Pacific Plate thrusts underneath North America. A very standard type of earthquake in this area.” 

The initial tsunami alert included upper Cook Inlet, from Homer to Hope, in warning status. Warning means to evacuate to higher ground. People on the peninsula — in Kenai, Ninilchik, Clam Gulch, Nikiski, even Cooper Landing — got a text alert to evacuate. That was not accurate, said Dan Nelson, with the Kenai Peninsula Borough Office of Emergency Management.

“They do not have a tsunami danger. Based on how the Cook Inlet is and how the bathymetry works, there’s not generally a tsunami danger as you come up this far up Cook Inlet. It does just stay around that Kachemak Bay area,” Nelson said. “So that’s why there was information going out as an automated message. That happens as a limitation to the technology that’s used by the federal government to do their warnings. And then you may have received a KPB Alerts later that said that area was not in the warning. And that’s why there is a bit of a conflict. It is an automated system it is designed to get that messaging out quickly but it does have a very broad coverage area.”

A tsunami warning was in effect for communities in Kachemak Bay.

“That means if you are in a low-lying area, move to high ground. Evacuate from areas such as the Homer Spit and any other low-lying areas,” Nelson said. “Homer High School is a good area. We recommend do not go to South Peninsula Hospital or any of the health care facilities so they can continue to handle their medical needs as they come through. In the Seldovia area, the Seldovia School is a good place. Look for those two schools. If you are a visitor to the area, there’s generally signage to help you find those.”

In Homer, Tracy Crowley was in her hotel room not far from the Homer Spit when she got the tsunami warning on her phone. Crowley says the front desk wasn't much help.

“They said they had no idea what the protocols were, that she was looking into it and that her manager was on the way and we could call back,” Crowley said.

But then the sirens sounded. Crowley and her friend got nervous and decided to drive toward high ground. They ended up on Diamond Ridge Road, parked in their rental car for hours, scrolling for information on their phones. They felt they were in a good spot but debated going down for gas or to the shelter the high school. They eventually heard the all-clear.

The Tsunami Warning Center initially predicted that a first tidal wave could hit Kachemak Bay at 1:25 a.m. Seward and Resurrection Bay were under alert status, to be ready to evacuate if needed. 

“Because of some of the technology used in the automation, there were warnings played over the sirens when there was not a warning for that area. So that’s why there was confusion with the warning and advisory for Resurrection Bay,” Nelson said.

A possible tidal wave was initially predicted in that area at 12:30 a.m. The Resurrection Bay alert was lifted at 12:05 a.m. The warning in Kachemak Bay was lifted at 12:30 a.m. Sand Point on the Alaska Peninsula was the first community predicted to see a wave. But, by 11:30 p.m., the Tsunami Warning Center reported that the observed wave height was only about 25 centimeters.

As of 3 p.m. Wednesday, there were nearly 50 aftershocks from the main quake, ranging in magnitude from 1.9 to 5.9.

For more information on the quake, visit the Alaska Earthquake Center.

Visint the U.S. Tsunami Warning System for more information on alerts and warnings.

The Kenai Peninsula Borough Office of Emergency Management posts updates on its Facebook page, KPB Alerts. To register to get KPB Alerts to your phone, visit kpboem.com and click the Register Here for KPB Alerts link on the left side of the homepage.  

Alaska Public Media’s Liz Ruskin and Lex Treinen contributed to this story.

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