A magnitude 7.3 earthquake struck about 55 miles south of Sand Point, about 300 miles from Dillingham, just after 12:30 p.m. yesterday. The quake shook communities across Bristol Bay and prompted a Tsunami warning in areas to the east of the bay.
“So the strongest shaking was felt close by in Sand point, King Cove, areas like that,” Michael West, a state seismologist with the Alaska Earthquake Center at UAF, said. “As you go further away as you start to get to Bristol Bay, Dillingham, or out to the east in the Kenai Peninsula, you will feel moderate shaking because you're further away, but for a large earthquake like this there is a bit more of a rolling motion to the ground.”
West says the impact of the earthquake likely took several minutes to travel from the epicenter to Bristol Bay. And he says the shaking may have lasted much longer than people realized.
“An Earthquake of this size takes probably 10 or 20 seconds for the actual rupture at the epicenter to happen,” West said. “You add on top of that waves bouncing around in the earth, though you might have only felt this earthquake for several seconds, the ground around you at some distance was surely gently swaying, perhaps unperceptively, for many, many tens of seconds.”
The earthquake happened at a fault line where two tectonic plates meet. West says that, in the big picture, an earthquake like this is geologically expected. He says Alaska is responsible for four out of five of the earthquakes in the United States, and most of Alaska’s earthquakes originate in the southern part of the state.
However, West says scientists are puzzled by an uptick in large earthquakes at this specific location along the fault line.
“What has our attention right now is that this is the 5th large earthquake, magnitude seven or above, in a very short area. Just over a couple of hundred miles in the last five years. So, compared to this whole two thousand miles of conduction zone along the Aleutians, this spot, kind of that sand point, Chignik area, appears to be going through an area of unrest right now.”
The largest earthquake at this spot in the last five years was a magnitude 8.2 in 2021. West says they currently don’t know what’s causing this surge in activity.
Soon after yesterday’s earthquake, the National Oceanic and Atmospheric Administration issued a tsunami warning in areas east of Bristol Bay. The warning was for the southern part of the Aleutian Chain and the eastern coast of the Alaska Peninsula, including Kodiak and the western Kenai Peninsula. Bristol Bay was outside of the inundation zone and never entered a Tsunami warning.
No significant waves were reported in any communities under warning; however, he says that for the areas within range, the warning was prudent.
“A magnitude 7.3 earthquake is absolutely capable of causing a harmful tsunami,” West said. “Now, that didn't happen, but the time available to communities close to this earthquake before a Tsunami would have reached them is really just a couple of minutes.”
The warning was downgraded to an advisory in the hours following the initial alert and was canceled roughly two hours after it was issued.
Although not the case yesterday, if a Tsunami warning is ever issued for Bristol Bay, guidance on tsunami evacuation zones for Dillingham can be found at Tsunami.alaska.edu.
