Alaska rocked by 7.1 magnitude earthquake. Is that normal?

Residents living in the Cook Inlet region of Alaska were jolted awake by a 7.1 magnitude earthquake early Sunday morning, leaving many without power.

Vincent Nusunginya via the AP
Boxes of cereal and bottles of juice lie on the floor of a Safeway grocery store following a magnitude 6.8 earthquake on the Kenai Peninsula on Sunday Jan. 24, 2016, in south-central Alaska. The quake knocked items off shelves and walls in south-central Alaska and jolted the nerves of residents in this earthquake prone region, but there were no immediate reports of injuries.

A magnitude 6.8 earthquake woke up sleeping residents of southern Alaska at 1:30 am Sunday morning. 

In its initial report, the US Geological Survey (USGS) registered the earthquake as a magnitude 7.1, downgraded it to 6.8, and then raised it back to 7.1. There are no deaths or serious injuries reported. The USGS also says Alaska is not in danger of a subsequent tsunami.

Everything was flying off the shelves,” Bob Candopolous of Seward told 2KTUU News. “It was tough to get to the front door to get out of the house.” 

The epicenter was located about 162 miles southwest of Anchorage, in the Cook Inlet region. 

“My husband came into the bedroom forcefully saying, ‘Get up! Get up!’ said,” Associated Press reporter Mark Thiessen. “But I was already awake, trying to figure out what was happening.” 

The earthquake may have surprised sleeping homeowners, but quakes are common in Alaska, particularly of this magnitude. The US Geological Survey (USGS) reports a magnitude 7 or greater earthquake someone in or offshore Alaska every one to two years on average

“This is a common type of event for this region and depth,” the University of Alaska Earthquake Center reports. “Earthquakes of similar sizes occurred in the Lower Cook Inlet in 1912 and 1933, but we do not have precise magnitudes and locations for that time period.” 

Of the almost 23,000 Alaskans who power their homes through Homer Electric Association, almost 5,000 are without power Sunday after the quake. The Matanuska Electric Association and Chugach Electric Association also reported 4,900 and 4,600 outages respectively, but by around 6:30 am Sunday morning the number of outages had been reduced to a little more than 100 each. 

2KTUU News also reports more than 20 homes in Kenai have been evacuated due to a possible gas leak.

“When it hit, it was just soft at first, and it just kept getting bigger,” Joshua Veldstra, a professional photographer who lives in Homer, told CNN. “It was one of those moments where you didn’t know if it was going to get worse or if it was going to calm down.” 

The Alaska Earthquake Center recorded about 30 aftershocks in the first two and half hours after the quake, including a 4.3 magnitude earthquake at 3:37 am local time. 

Earthquakes occur in Alaska because of stresses between two tectonic plates: the Pacific Plate and the North American Plate. The Pacific Plate moves about two inches northward each year and it is pushed below, or “subducts,” beneath the North American Plate. The Yakutat block, an irregularity on the top of the Pacific Plate, prevents a smooth subduction. 

While Sunday morning’s earthquake was damaging, it was far less destructive than the 1964 Great Alaska Earthquake, the second largest global earthquake ever recorded. Noted as the largest earthquake in Alaska by the USGS, the Great Quake occurred on March 27 with a magnitude of 9.2. The quake triggered a tsunami that destroyed many towns along the Gulf of Alaska. One hundred thirty-one people were killed by the 1964 quake, 9 from the earthquake itself and another 122 from the ensuing tsunami.   

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