A magnitude 7.9 earthquake struck about 170 miles southeast of Kodiak, Alaska early Tuesday morning, sending residents of the picturesque island fleeing to higher ground to avoid tsunami waves. The quake also prompted tsunami alerts along the West Coast of the U.S. and Hawaii, but those were canceled after data showed damaging waves were not expected.
Since the first quake hit there have been several aftershocks, some of which have been strong earthquakes themselves, with a magnitude of up to 5.3 on the Richter Scale. Reports indicated water fluctuating by up to 1 foot in a channel that feeds into Kodiak Harbor, but no large, damaging waves.
Tsunamis are caused by earthquakes, when sudden shifts in the seafloor displace enough water to set in motion waves at the surface that can travel across an ocean in a matter of hours.
The magnitude 7.9 earthquake occurred along a "strike-slip" fault, where two plates grind past one another. These earthquakes don't typically give rise to large tsunamis, since they tend to involve horizontal, rather than vertical, motion.
This morning's 7.9 earthquake occurred along a strike-slip fault. The horizontal movement of the two plates in a strike-slip fault, typically limits the threat of tsunami's pic.twitter.com/o7kgwNHqxS
— Greg Diamond (@gdimeweather) January 23, 2018
Alaska has a long history of powerful earthquakes and tsunamis.
People who live along the coast are well aware of the need to get to higher ground during a tsunami threat.
So far we are ok and sheltering together, listening to radio - sirens still going and warning in effect. Stay safe out there peeps, and get to higher ground. #earthquake #alaska #kodiak pic.twitter.com/E6gCWegvWq
— Lisa Hupp (@LisaHupp) January 23, 2018
Experts are warning of the continued threat of aftershocks, some of which could be as strong as magnitude 6.0.
Alaska's Kodiak Police Department told residents in a video posted 20 minutes ago to evacuate their homes and move to ground at least 100 ft or higher amid tsunami alert. pic.twitter.com/biU8XaEnr3
— NBC Nightly News with Lester Holt (@NBCNightlyNews) January 23, 2018
This quake was on the stronger side, but was not the strongest earthquake on record to strike the state.
In 1964, Alaska was hit by an earthquake of magnitude 9.2 intensity. This remains the most powerful earthquake in North American history, and it caused widespread damage in south-central Alaska, along with about 140 deaths.