A tsunami alert has just been issued for the western coast of north America.
TSUNAMI MESSAGE NUMBER 2
NWS PACIFIC TSUNAMI WARNING CENTER EWA BEACH HI
1220 AM HST TUE JAN 23 2018
TO - EMERGENCY MANAGEMENT IN THE STATE OF HAWAII
SUBJECT - TSUNAMI WATCH SUPPLEMENT
A TSUNAMI WATCH CONTINUES IN EFFECT FOR THE STATE OF HAWAII.
AN EARTHQUAKE HAS OCCURRED WITH THESE PRELIMINARY PARAMETERS
ORIGIN TIME - 1132 PM HST 22 JAN 2018
COORDINATES - 56.0 NORTH 149.2 WEST
LOCATION - GULF OF ALASKA
MAGNITUDE - 8.2 MOMENT
BASED ON ALL AVAILABLE DATA A TSUNAMI MAY HAVE BEEN GENERATED BY
THIS EARTHQUAKE THAT COULD BE DESTRUCTIVE ON COASTAL AREAS EVEN
FAR FROM THE EPICENTER. AN INVESTIGATION IS UNDERWAY TO DETERMINE
IF THERE IS A TSUNAMI THREAT TO HAWAII.
IF TSUNAMI WAVES IMPACT HAWAII THE ESTIMATED EARLIEST ARRIVAL OF
THE FIRST TSUNAMI WAVE IS
0423 AM HST TUE 23 JAN 2018
Thinks that's been revised to 7.9 magnitude
It seems that there might be no tsunamis after all.
Warnings are still in place but the time has passed now that any effects would have shown up in Kodiak.
Kodiak is near to the epicentre of the earthquake.
A scary warning to wake up to in the middle of the night none the less
According to Twitter a lot of people slept through the warnings.
News reports here state that most people heeded the tsunami warning sirens and went to higher ground (this would be mostly in outer coastal areas of Vancouver Island and further north), but after they arrived the tsunami alert was cancelled and nothing happened, so all good.
Any idea as to how many alerts have been issued since the system went into operation and how many were eventually validated?
No idea, will try to find out. I don't think they sound these sirens (in B.C.) very often, seems that it was automatic on receipt of earthquake in given location and magnitude, then later it was realized by earthquake analysts that it was of the wrong sort to create a tsunami but the cancellation was about the same time that the wave was supposed to arrive.
We haven't had many large quakes that distant in recent years, the only test cases have been almost immediate local warnings that have generally been on such a short time cycle that people just ran for higher ground when they felt the shaking but those turned out to be too small in magnitude to create big tsunamis even where the quake was felt.
There has not been anything very actionable here since a large tsunami with the March 1964 earthquake (believe that was 9.2) near Valdez AK, and that one did considerable damage on west coast of Vancouver Island with some drownings, hence the warning system.
I think people out on the "outer" coast are very aware of these warning systems, but if one ever went off in the more sheltered inner coasts near bigger cities, I doubt that people would necessarily respond, in fact I don't even know what parts of the inner coast have that system in place. A quake in just the right spot in Puget Sound or the Strait of Juan de Fuca might cause a tsunami further inland but it has never happened in the two centuries of our recorded history, some archaeological indications that a big quake in Japan in 1700 sent a devastating tidal wave across the Pacific and did enormous damage to coastal native settlements.
Generally speaking this whole region (BC, WA) is living in the expectation that we are long overdue for something large-scale, Mount Rainier going volcanic being the most significant worry, then a damaging earthquake off the west coast or in Puget Sound. We had a rather minor one in Feb 2002 that still did quite a bit of damage in Seattle, and they get 5-6 on Richter scale tremors all the time near the coast. I've felt two myself in the 22 years we lived there. But it's "tick tock" on the Big One.
Astonishing amount of aftershocks in the region, plate is very active
Something Shocking Happened in Florida After the Alaska Earthquake: Well Water Levels Changed
What Are Seismic Waves? - -> http://www.geo.mtu.edu/UPSeis/waves.html
The response of well-aquifer systems to seismic waves - -> http://onlinelibrary.wiley.com/doi/10.1029/JZ070i016p03915/abstract
Here is an example from a well in Virginia, note the spike on Jan 23