No Tsunami Associated with Sizable Aleutian Earthquake


Annie Ropeik/KUCB
A powerful underwater earthquake in the Western Aleutians triggered tsunami alerts for the Aleutian and Pribilof islands Monday afternoon.
No damages were reported after the magnitude 8.0 quake, recorded just before 1 p.m. on Monday. It happened about 30 miles northwest of Amchitka, about 60 miles underwater.
Residents in the Western Aleutians reported feeling shaking during the quake, according to the Alaska Earthquake Information Center. And the quake has set off a series of aftershocks, some as strong as a magnitude 6.
The earthquake also generated a tsunami warning from Attu to Nikolski and in the Pribilof Islands for about two hours Monday. It was then downgraded to an advisory.
The Unalaska area, from Nikolski to Unimak Pass, was also under an advisory for part of Monday afternoon. It ended around 4 p.m.
The tsunami alerts stemmed from the force of the quake. But the Earthquake Center’s Natasha Ruppert says tremors at such a depth don’t often create tsunamis.
“Well, based on its magnitude, there is definitely potential for tsunami in the Aleutian Islands. But based on its depth, I do not expect that there will be a significant tsunami from this earthquake.”
The National Oceanic and Atmospheric Administration observed tsunami waves about a foot in height or less in Unalaska, Adak and other islands in the region. Those waves are measured at the highest water level above the tide level. They weren’t high enough to do any damage.
Unalaska’s Department of Public Safety told residents to avoid beaches and harbors during the advisory, but there was no full-scale evacuation to high ground.
Monday’s earthquake was near an active volcanic island in the Western Aleutians. Semisopochnoi Island has been undergoing a series of small quakes – most around magnitude 2.0 – for the past couple of weeks. But the AEIC’s Ruppert says the activity isn’t connected.
"All earthquakes that are related to volcanoes, they are very shallow, right beneath the surface, and this one is about 100 kilometers deep.”
It was a busy day for earthquakes in the Pacific, though — another one with a magnitude 7.2 was recorded in the South Pacific, off New Zealand, about an hour and half before the quake in the Aleutians. Ruppert says it’s possible that one triggered the other – but they don’t know for sure.

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