Alaska Earthquake 7.9

[bing101]

https://www.cnn.com/2018/01/23/us/alaska-earthquake/index.html

There was a Tsunami warning for the Pacific rim but that's been called off.

[oscar]

Off-shore earthquake, apparently causing no significant damage (but some inconvenience) on-shore in Alaska.

[jakeroot]

I was browsing Google Maps around Aberdeen, WA last night, when the Tsunami warning popped up (the built-in warning that Google Maps displays in a grey box). When I read 8.0, I just about shit my pants. But the depth of 20 km eased my worries a bit. Heard there was some shaking in coastal Alaska, but otherwise, a non-event.

[Bruce]

Really fortunate this was a strike-slip event rather than a megathrust, which is what produces large tsunamis.

Also good that the alarms and alerts mostly worked, and residents in Alaska evacuated in a pretty calm and orderly manner, according to the Anchorage Daily News. We need to get good at evacuating the coasts.

[Hurricane Rex]

7.9 seems large but when you see the damage, I'm really grateful it wasn't worse.

[ET21]

Wasn't sure if these were true reports, but I heard a couple volcanoes erupted due to the quake in Alaska. I know that much of the Pacific Rim from Cali to AK was put on high alert for possible eruptions but haven't heard anything since.

[triplemultiplex]

I only see unrelated volcanic activity in the Aleutian chain at two places.

Interesting to look at the epicenter compared to most activity in the region; it's kind of an outlier so far south of the actual plate boundary.



An 8.0 is usually only strong enough to generate a local tsunami, if at all.  There isn't enough movement to displace enough water for the wave to propagate across an entire ocean basin.

When I was in Hawaii, there was a quake about this size in Chile and there was a brief tsunami watch while quake magnitude was being assessed.  It's standard practice to send out these alerts as soon as a quake of sufficient magnitude is detected.  Just in case.  Later as more data is received from other monitors and the nearest tsunami buoys, the alert can be upgraded or cancelled as circumstances dictate.  But at the time, as soon as the updated magnitude was reported, I knew there would be no danger where I was. 

[Bruce]

Wasn't sure if these were true reports, but I heard a couple volcanoes erupted due to the quake in Alaska. I know that much of the Pacific Rim from Cali to AK was put on high alert for possible eruptions but haven't heard anything since.

There hasn't been any volcanic activity in North America related to this earthquake. While some very large earthquakes can trigger volcanic activity, they are usually megathrust quakes that deform the subducting plate.

There has been some earthquake activity around Mount Rainier and Mount St. Helens recently, but the USGS and PSNS determined that it was just normal rumblings rather than a sign of impending doom.

[Bruce]

An 8.0 is usually only strong enough to generate a local tsunami, if at all.  There isn't enough movement to displace enough water for the wave to propagate across an entire ocean basin.

Tsunami generation is more dependent on the type of movement (a slip like this one won't generate enough vertical movement to trigger waves) than the size of the initial earthquake. There's been plenty of similar offshore earthquakes in the 7.5 ~ 8.0 range that create waves of over 30 feet (e.g. 1983 Akita and 1993 Hokkaido).

[triplemultiplex]

Exactly.  Those were local tsunamis.