If you’re from Alaska (like me) then you’re no stranger to the rattling, window shaking quakes that jolt so many of us upright in the middle of the night. You’ve definitely felt earthquakes more times than you’ve seen the northern lights and, chances are, you’ve evacuated to higher ground on at least one occasion.
At 12:31 am thousands of Alaskans were woken up by a 7.9 magnitude earthquake that struck 181 miles southeast of Kodiak Island in the Gulf of Alaska. It prompted tsunami warnings all over Alaska, the US west coast and British Columbia. It’s just one of the 1,000 earthquakes the state will see just this month.
These earthquakes and volcanoes are the results of a process called subduction. It occurs along tectonic plates – divisions in the earth’s crust – and the Gulf of Alaska is located on the boundary of two of the largest.
Under most of Alaska, the Pacific Plate is being pushed under the North American Plate to form a subduction zone. The two can move smoothly over each other or become stuck. When stuck, they build up strain and eventually release the intense force that causes earthquakes.
Alaska is one of the most seismically active areas in the world and has more earthquakes than any other region. It also has big ones. On average, one “Great” earthquake – magnitude eight or larger – will rock the state every 13 years.
This earthquake was a big one, but not the big one geologists say will destroy a portion of the coastal Northwest.
It’s a game of tectonic roulette depending on where that pressure is accumulating. Tuesday’s earthquake was not generated where the Pacific Ocean seafloor slides under the North American plate, but rather farther out where the fault moves horizontally. It’s called a strike-slip earthquake and it’s less likely to trigger large tsunamis, which is is why Alaska saw waves of less than a foot.
Earthquakes on the subduction zone itself, however, move vertically on the seabed and cause devastating results – like the magnitude 9 earthquake in Japan that triggered 126 foot waves and killed 20,000 people in 2011, the 2004 quake off the coast of Indonesia that caused a tsunami that killed more then 200,000 people, or the 1964 9.2 magnitude Alaska quake that was the most powerful in the US and killed 100 people.
“I’ve been through earthquakes before so I kept my head on my pillow waiting for it to end,” said Kodiak resident Megan Roderick in an interview with IFLScience. “The intensity increased within seconds. My bed felt like a bad motel massage.”
The United States Geological Survey says little to no damage was caused by the quake, and some Alaskans were equally unfazed.
“It felt like any other earthquake, so I went back to sleep and didn’t think anything of it,” Anchorage middle school teacher Patrick McCormick told us. “I would have forgotten about it.”