A powerful earthquake in Alaska didn’t trigger a big tsunami — here’s why
Last night, a magnitude 7.9 earthquake struck southeast of Kodiak Island in the Gulf of Alaska, prompting a tsunami warning that forced people to flee to higher grounds in the middle of the night. Fortunately, the tsunami waves were less than a foot high, and the advisories were canceled a little after 4AM local time. So why was Alaska so lucky?
“Alaska is no stranger to these kinds of quakes,” says Don Blakeman, a geophysicist with the US Geological Survey (USGS).
Last night’s earthquake generated because of all the strain building up on the subduction zone, but it did not occur exactly on a fault where the Pacific Ocean seafloor is sliding under the North American plate, Blakeman says. Instead, the quake occurred a little farther out, in a place where the fault is moving horizontally. This type of quake, called a strike-slip earthquake, is less likely to trigger large tsunamis, and this is probably why Alaska only saw waves of less than a foot, according to Blakeman.
When earthquakes happen on the subduction zone itself, where one plate is pushing down while the other is going up, then high waves form. “To get a tsunami, you have to have substantial vertical movement on the seabed,” Blakeman says. Those types of earthquakes were responsible for the massive tsunamis in Japan and Indonesia.
https://www.theverge.com/2018/1/23/16922914/alaska-earthquake-tsunami-pacific-north-america-plate-boundary
= new reply since forum marked as read
