Biggest Alaska quake in years, but no tsunami? Here's why
Tuesday, January 23, 2018, 12:35 - On March 11, 2011, a magnitude-9 earthquake shook northeastern Japan, triggering a devastating tsunami.
In 2004, the Banda Aceh earthquake, a magnitude-9.1 tremor that triggered a tsunami in Sumatra, killed more than 230,000 people.
So, with these relatively recent disasters in mind, when a magnitude-7.9 earthquake struck off the coast of Alaska early on January 23, 2018, it had people running for their lives, fleeing in their cars and getting to higher ground.
In the end, nothing happened. No wave, no tsunami. Great outcome, but why did it happen that way? We explore below.
Why do earthquakes occur in this area?
The Pacific Ring of Fire is to blame for tectonic plate movement in Alaska and in Asia. The Pacific Plate, and how it interacts with other plates, has created movement in our Earth's crust over millions of years helping to create the tallest mountains on our planet.
The Alaska area sits on an important subduction zone, an area where one plate slides beneath another into the mantle, the hotter layer beneath the Earth’s crust. In this case, the Pacific Plate is subducting beneath the North American Plate, and the great plates are rough and stick together, building up energy that is released as earthquakes. However, there are different types of quakes that can happen along the boundaries of these subduction zones.
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This earthquake was different, and that was a good thing
According to the United States Geological Survey: "The deepest earthquakes occur within the core of subducting slabs - oceanic plates that descend into the Earth's mantle from convergent plate boundaries, where a dense oceanic plate collides with a less dense continental plate and the former sinks beneath the latter."
These types of earthquakes are the most intense and usually the deadliest. This was the type of earthquake in Japan in 2011 and in Sumatra in 2004.
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Fortunately, the earthquake in Alaska on January 23, 2018 was a different type of quake known as a strike-slip earthquake. You can think about it as a sliding motion of a person brushing by your arm on a subway car, only on a tectonic scale, and strike-slip quakes are not nearly as dangerous as the kinds of earthquakes that struck in Japan and Sumatra.
The source of many of the earthquakes in the Alaska area is the Denali Fault System, extending for 745 miles along the boundary between the Pacific and North American plates.
It is here where we see movement in more of a side-to-side nature rather than vertical earth movement. Strike-slip faults with left-lateral motion are also known as sinistral faults. Those with right-lateral motion are also known as dextral faults. A strike slip earthquake is what occurred in Alaska, and as a result did not trigger major tsunami.
When was the last major quake in Alaska?
On March 28, 1964, the Gulf of Alaska was devastated by the Prince William Sound earthquake which measured magnitude-9.2 on the Moment Magnitude Scale.
It caused landslides in Anchorage and raised parts of outlying islands by as much as 36 feet. The resulting tsunami reached heights of 200 feet as it swept into the shallow Valdez Inlet. 128 people died in this event, which also caused $311 million worth of damage.
Unlike this week’s quake, this tremor was a “megathrust” earthquake, occurring where the oceanic plate descends underneath a continental plate in southern Alaska.
Warning time was enough to get people prepared
The good news is that through social media, many people were able to get a to a safe spot quickly. People were broadcasting live on Facebook, allowing the world to watch in real time as, as far as anyone knew, a potential tsunami hammed. In the end, there was no such tsunami, thank goodness, and people along the West Coast of North America were able to put their minds at ease and return to their homes very soon after.
For continued coverage and updates on this developing story stay tuned to The Weather Network.