Alaska Quake

Felt it in Fbks, nothing much but it did last a while (~45 seconds). My wife is in ANC, and even though she's been in a bunch of quakes, this one freaked her out a bit. She's OK and should drive back up tomorrow unless the alternate route out of ANC is closed by then.
 
My son happened to be in Anchorage this morning when the quake struck ... he was on the 5th floor of the PDC Engineering building ... he messaged my wife within minutes of it happening to let her know that he was okay and safe. He did say that it was pretty scary ... bookcases tipping over, computer monitors crashing to the floor, file cabinets flying open, everything shaking. He was able to fly out of Anchorage later on and go back up to Fairbanks.
 
crazy how much damage the soil liquefaction did. When we had the 6.9 in Hawai'i we barely had any damage.
But we have a lot of basaltic bedrock, so this helped.
These big quakes can be pretty scary. This one in Alaska was just a bit stronger than the ones we had this year but nothing you really wanna experience
 
I know that, we do the magnitude calculations and energy release formulas all the time.
But a lot has to do with soil and bedrock in certain areas.
A 7.0 in Alaska will always feel stronger than a 7.0 in Hawai'i and create more damage. The energy released in both areas will be about the same, but ground movement will be way different and therefore more damage in Alaska
 
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I would disagree. A 7.0 will feel like a 7.0 anywhere. Because it's measured by instruments that FEEL it. The damage it causes will be different because of liquefaction and such.
 
Magnitude and Intensity measure different characteristics of earthquakes. Magnitude measures the energy released at the source of the earthquake. Magnitude is determined from measurements on seismographs. Intensity measures the strength of shaking produced by the earthquake at a certain location. So you might feel a 7.0 differently in different areas the same distance from the epicenter, even though the magnitude is the same.

Intensity is also determined by reports from people as to what they felt. Very subjective, but valuable info. If you look on the USGS website, they always have a part asking people to report what they felt and observed during an earthquake. The name for this particular scale is the Modified Mercalli Intensity Scale, and the Richter measures the magnitude.

As for liquefaction, yes, Anchorage is going to see more intensity and damage from an earthquake because of that than would Hawaii. Incidentally, SLC is also at high risk for the same reason. In one of my geology classes, I asked the prof about how W. Colorado would fare if SLC had a big quake. He said a lot of E. Utah wouldn't see much damage, but when the waves got to the Grand Valley (Grand Junction), there could very well be some damage from liquefaction. (This was a prof at Utah State.)

Here's a quote from a USGS website:

The severity of an earthquake can be expressed in terms of both intensity and magnitude. However, the two terms are quite different, and they are often confused.
Intensity is based on the observed effects of ground shaking on people, buildings, and natural features. It varies from place to place within the disturbed region depending on the location of the observer with respect to the earthquake epicenter.

Magnitude is related to the amount of seismic energy released at the hypocenter of the earthquake. It is based on the amplitude of the earthquake waves recorded on instruments which have a common calibration. The magnitude of an earthquake is thus represented by a single, instrumentally determined value.

https://pubs.usgs.gov/gip/earthq4/severitygip.html
 
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Nick said:
I would disagree. A 7.0 will feel like a 7.0 anywhere. Because it's measured by instruments that FEEL it. The damage it causes will be different because of liquefaction and such.
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I can only speak of the 20,000 earthquakes I experienced this year. Hundreds of them where were 5.2 or bigger. Thousands were small, like 4.5ish
Some of the quakes I experienced in Hilo, they had the same strength as the ones I experienced in Volcano or at my place. They felt way stronger in Hilo because of different soil and bedrock. They even did more damage there.
I was surprised that a 6.9 quake did damage a lot of buildings there while I had just massive shaking and everything was tossed around.
And the epicenter was in both cases the same distance. Hilo had less bedrock, but more soil prone to liquefaction.

Heard similar stories from other people at different places as well. Especially some neighbors who had moved from California. There they felt a 6.9 did way more damage and it felt much stronger to them than the 6.9 they just experienced in Hawai'i. That was also because of liquefaction. So magnitude plays a major role as well as intensity.
 
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See my post above yours, @Yvonne. Magnitude is not subjective, intensity is, which I think is the same thing you're saying.
 
It’s interesting to follow the aftershocks.

https://earthquaketrack.com/recent

It used to be that seismologists thought aftershocks didn’t last too very long, but newer research shows otherwise. They’re finding evidence of aftershocks still happening from the Alaska quake of 64.
 
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Rockskipper said:
It’s interesting to follow the aftershocks.

https://earthquaketrack.com/recent
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they can go on for months.

When we started with our earthquake swarm, we had a quake every two minutes.
Then several foreshocks over a few days, the main quake and massive aftershocks. They were often between 3.5 and 5.6.
Day and night. Every two to three minutes. Your bed shakes continuously.
But after a week or so you'll get used to it. :-)
And then you wait for the daily 5+ quake
 
Yvonne said:
they can go on for months.

When we started with our earthquake swarm, we had a quake every two minutes.
Then several foreshocks over a few days, the main quake and massive aftershocks. They were often between 3.5 and 5.6.
Day and night. Every two to three minutes. Your bed shakes continuously.
But after a week or so you'll get used to it. :)
And then you wait for the daily 5+ quake
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I don't think I could ever get used to it. And I'm glad I'm not in a seismically active area, though I'll be up by Yellowstone soon. I think if the supervolcano were to blow, I would want to be right there so I wouldn't know what hit me. Yikes.

This guy's a geology prof and is so bad he's almost good. He puts out these vids for his classes where he sings as you learn. :)

 
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Not arguing with anyone here but as I learned in my Physical Geology class, and heard again from one of our earthquake trained engineers yesterday, the duration of the shaking is a really big determinant of the damage caused to infrastructure. We felt it in Fbks for nearly 45 seconds which is an eternity for a shaking building or highway.
 
Outdoor_Fool said:
Not arguing with anyone here but as I learned in my Physical Geology class, and heard again from one of our earthquake trained engineers yesterday, the duration of the shaking is a really big determinant of the damage caused to infrastructure. We felt it in Fbks for nearly 45 seconds which is an eternity for a shaking building or highway.
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45 seconds is crazy. NO wonder so much damage.
And I thought that 25 seconds were already weird and long
 
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