[Alaska] Largest Earthquake Since 1964 (1 Viewer)

[Glitch]

Magnitude 8.2 Earthquake in Alaska

A magnitude 8.2 earthquake struck 50 miles south of the Alaska Peninsula on July 28, 2021 at 10:15 pm local time (July 29, 2021 06:15 UTC). Seismic instruments indicate the earthquake originated at a depth of 20 miles (32.2 kilometers).

www.usgs.gov

As some may be aware, there was a rather large earthquake just off the coast of Alaska July 28, 2021. With a magnitude of 8.2 that makes it the largest earthquake since the 9.2 earthquake on Good Friday in 1964. There have already been three magnitude 7.9 earthquakes since 2000, but nothing bigger until Wednesday.

The earthquake occurred very close to where the Pacific tectonic plate is subducting under the North American tectonic plate, and often the location of the bigger earthquakes. In January 2018 there was a 7.9 earthquake ~250 miles due east of this more recent earthquake, also very close the subduction trench.

Neither this earthquake nor the one in 2018 produced much of a tsunami. In both cases the tsunami warning was issued, but when the tsunami wave measured less than one foot tall at its peak, the warning was canceled. That is the key difference between this 2021/2018 earthquakes and the 1964 earthquake. In 1964 as much as 12,000 square miles of the earth's surface was lifted from three to eight feet. Which is what created the devastating tsunami in 1964. The 2021 and 2018 earthquakes appear to have shifted horizontally rather than vertically.

 

[bongsaway]

Blinded by science it's the end of the world as we know it.

 

[venice_ca]

In 1964 as much as 12,000 square miles of the earth's surface was lifted from three to eight feet. Which is what created the devastating tsunami in 1964.

My family was at our beach house in Oxnard, and while we children slept through the tsunami warning, my parents were debating whether or not to evacuate inland -- meaning go back to our home in an inland valley. They stayed, and Crescent City was hit be a tsunami.

Within a week or so, we could see the activity at the Port Hueneme Navy Construction Battalion Base -- the SeaBees were going to Alaska to help with the quake relief and repair.

We've had our share of major quakes in Southern California, but not one lasting anywhere near four minutes (must seem like an eternity!) and nothing as strong as 8+ in more recent times.

I'm in a designated tsunami zone, but because of local conditions in the Santa Monica Bay, the expectations of one reaching here is small. Not so for other beaches on the So Cal coast.

Chile has suffered a number of devastating earthquakes in this century, the worst registering 8.8, 8.3, and 8.2 respectively.

The Pacific Rim makes life exciting, not necessarily in a good way.

 

[Roadvirus]

That'll rattle the dishes for sure.

 

[Roadvirus]

Blinded by science it's the end of the world as we know it.

But i feel fine

 

[EMNofSeattle]

My family was at our beach house in Oxnard, and while we children slept through the tsunami warning, my parents were debating whether or not to evacuate inland -- meaning go back to our home in an inland valley. They stayed, and Crescent City was hit be a tsunami.

Within a week or so, we could see the activity at the Port Hueneme Navy Construction Battalion Base -- the SeaBees were going to Alaska to help with the quake relief and repair.

We've had our share of major quakes in Southern California, but not one lasting anywhere near four minutes (must seem like an eternity!) and nothing as strong as 8+ in more recent times.

I'm in a designated tsunami zone, but because of local conditions in the Santa Monica Bay, the expectations of one reaching here is small. Not so for other beaches on the So Cal coast.

Chile has suffered a number of devastating earthquakes in this century, the worst registering 8.8, 8.3, and 8.2 respectively.

The Pacific Rim makes life exciting, not necessarily in a good way.

I visited Chile three years ago and visited Valdivia several years ago where the giant earthquake hit in the early 1960s. There is still ruins in Valdivia from the earth quake.

there’s a several parking lots (a rarity in Chile) in Valdivia that were city blocks destroyed by the quake. Also the old Spanish forts there where Lord Thomas Cochrane “the sea wolf” conquered to win Chile’s independence from Spain are ruins. The parapets remain but the Spanish architecture were destroyed

 

[Court Jester]

In the mid 90s we were on vacation in Hawaii (north shore Oahu) and there was a tsunami warning due to large quake off the coast of Japan. I was amazed as one growing up in SoCal near the beach how seriously they take tsunami warning in Hawaii. There was a knock on our hotel door with an employee advising us of the warning with instructions, and where to evacuate to until there was an all clear. They offered help with transportation if needed, but we were required to evacuate. Where we were told to go was a nearby elementary school on higher ground, but it didn't look too appealing, so I grabbed a phone book and found a map showing other evacuation spots, and I chose the Mormon Birgham Young University a few miles away as they had more space, and some nice shady green spots to hang out.

We hunkered down for about 4 hours until "the wave" arrived, which turned out to be less than a foot. But they do take it seriously, I don't blame them. Other tsunamis have been devastating around the world.

 

[swing_voter]

I talked to a guy who was in Alaska for the 1964 quake. He said it looked just like the movies with crevasses opening up in the ground. Him and his mom clung to a tree in the yard until it was over.


.

 

[joko104]

I'm hoping for an earthquake in my bed soon. Hopefully she'll be back in the next few days.

 

[Colin Norris]

Blinded by science it's the end of the world as we know it.

Really?
How so?

 

[bongsaway]

Really?
How so?

It's a joke, two songs combined into one sentence.

 

[Glitch]

I talked to a guy who was in Alaska for the 1964 quake. He said it looked just like the movies with crevasses opening up in the ground. Him and his mom clung to a tree in the yard until it was over.

The ground opening up with crevasses during an earthquake is a common occurrence in Alaska. This was from the November 30, 2018 magnitude 7.1 earthquake whose epicenter was just three miles from my home:

M7.1 November 30, 2018 Anchorage Earthquake | U.S. Geological Survey

A magnitude 7.1 earthquake struck north of Anchorage, Alaska, on November 30, 2018, at 8:29 a.m. local time (17:29:28 UTC).

www.usgs.gov

 

[venice_ca]

The ground opening up with crevasses during an earthquake is a common occurrence in Alaska.

Is there a reason for this? Does this depend on a certain type of soil?

Our nightmare is liquefaction, not crevasses.

 

[Glitch]

Is there a reason for this? Does this depend on a certain type of soil?

Our nightmare is liquefaction, not crevasses.

The Susitna and Matanuska Valleys are filled with several hundred feet of glacial silt and clay. So liquification is a factor, and the reason behind the large cracks. The last photograph in my post above is a good example of the ground radiating out in all directions, like a ripple on a pond that was frozen in time just a few seconds after being created, and the ground dropping by about six feet in the center.

All the earthquakes I've experienced since moving to the valley have been rolling, like waves. Whereas, when I was living in Anchorage, near the base of the Chugach mountain range on bedrock, every earthquake felt like a sudden jolt with more violent shaking.

 

[venice_ca]

The Susitna and Matanuska Valleys are filled with several hundred feet of glacial silt and clay. So liquification is a factor, and the reason behind the large cracks.

All the quakes that I have experienced have been while living in an area with alluvial soil, but no crevasses, perhaps because the quakes were not in the 8+ range. (There was wide-spread damage to water, gas, and sewer lines.) Also, in the 1994 Northridge quake, the San Fernando Valley floor only rose a few inches, instead of feet.

All the earthquakes I've experienced since moving to the valley have been rolling

Same here until 1994, when there was vertical thrusting instead of horizontal waves. I distinctly remember standing in a doorway and having the floor coming up to hit my bare feet. The majority of Los Angeles area seismic reinforcements had been done to protect against lateral shaking, and consequently an overpass of a major freeway collapsed. Local building codes were updated, and CalTrans started more retrofitting of freeways.

Thanks for the discussion.

 

[Glitch]

All the quakes that I have experienced have been while living in an area with alluvial soil, but no crevasses, perhaps because the quakes were not in the 8+ range. (There was wide-spread damage to water, gas, and sewer lines.) Also, in the 1994 Northridge quake, the San Fernando Valley floor only rose a few inches, instead of feet.



Same here until 1994, when there was vertical thrusting instead of horizontal waves. I distinctly remember standing in a doorway and having the floor coming up to hit my bare feet. The majority of Los Angeles area seismic reinforcements had been done to protect against lateral shaking, and consequently an overpass of a major freeway collapsed. Local building codes were updated, and CalTrans started more retrofitting of freeways.

Thanks for the discussion.

I moved to Alaska from Reseda in 1991, so I missed out on the Northridge quake, but I was living in Palmdale during the 1971 6.5 magnitude Silmar quake. I remember watching the streets of Palmdale rippling like waves during the aftershocks.

I read somewhere that the San Andreas was not capable of generating an 8.0 magnitude or better quake, but I do not understand how they can make such a claim. Just because it hasn't produced an 8.0 quake in recorded history does not necessarily mean that it is incapable of producing such large quakes.

I'm a bit jaded these days. A magnitude 6.0 quake use to be a big deal to me. Now, not so much. We get a magnitude 6.0+ quakes every few months, and magnitude 7.0+ quakes every other year at least.

A lot of that has to do with the 70+ active volcanoes in Alaska. Most of them are located in the Aleutian Islands, with a few of the bigger volcanoes located in the Alaskan Peninsula, ~250 miles from my home. The Iliamna volcano, for example, had 44 quakes this past week with the largest being a magnitude 6.5, so they have increased the threat level.

The Iliamna volcano sits next door to the Mount Redoubt and Mount Spurr volcanoes. I have been covered in ash by both Mount Redoubt and Mount Spurr eruptions in the last 30 years. All three are located next to Novarupta (a.k.a. Valley of Ten Thousand Smokes), which was the location of the largest eruption of the 20th Century in 1912. The eruption was 30 times the size of the 1980 Mount St. Hellens eruption and 2.5 times bigger than the 1991 Pinatubo eruption.

Novarupta - The Most Powerful Volcanic Eruption of the 20th Century

The story of Novarupta - sometimes referred to as the Katmai eruption - which occurred in 1912 and was the most powerful volcanic eruption of the 20th century.

geology.com

 

[venice_ca]

I moved to Alaska from Reseda in 1991, so I missed out on the Northridge quake, but I was living in Palmdale during the 1971 6.5 magnitude Silmar quake. I remember watching the streets of Palmdale rippling like waves during the aftershocks.

I was in the SF Valley for the Sylmar quake (went to Birmingham High School) -- so much water sloshed out of my parents' pool. Trying to get news on the radio about what had happened, I found a San Diego station. The announcer was in a panic saying that a major quake had hit Los Angeles and knocked the radio stations off the air. I fell apart hearing the announcement -- I was OK until I heard what I had experienced put into words.

A lot of that has to do with the 70+ active volcanoes in Alaska. Most of them are located in the Aleutian Islands

I periodically check the US Geological Service for latest quakes, especially after we've had one locally. I notice that something nearly always shows up for Alaska, usually around the Aleutian Islands.

The Iliamna volcano, for example, had 44 quakes this past week with the largest being a magnitude 6.5, so they have increased the threat level.

Like in Pompeii before Vesuvius erupted . . .

I have been covered in ash by both Mount Redoubt and Mount Spurr eruptions in the last 30 years.

The ash we have here is from wildfires in the Santa Monica Mountains. None so far this year - knock wood.

Thanks for the information on the 1912 eruption. So much power and destruction unleashed.

 

[Glitch]

I periodically check the US Geological Service for latest quakes, especially after we've had one locally. I notice that something nearly always shows up for Alaska, usually around the Aleutian Islands.

Since I live in a forest, my primary concern are wildfires. So I regularly check their status during the Summer. Volcanoes are low on my list of concerns, but I do check to see if threat levels have changed periodically. I can't really do anything about earthquakes, other than hope if they are bigger than 7.0M the epicenter is more than 100 miles away.

I had my home custom built in 2003, just after the November 2002 7.9M Denali quake that shook the ground for almost two minutes continuously. So I made certain that every corner of the home was well braced for quakes, and I used 2x6 studs instead of 2x4. I have fire insurance for my home, but no earthquake insurance. So far it has withstood a 7.1M quake with an epicenter that was only 3 miles away without damage. Not even a crack in the drywall.

 

[Roadvirus]

The ground opening up with crevasses during an earthquake is a common occurrence in Alaska. This was from the November 30, 2018 magnitude 7.1 earthquake whose epicenter was just three miles from my home:

View attachment 67345745View attachment 67345746View attachment 67345747

M7.1 November 30, 2018 Anchorage Earthquake | U.S. Geological Survey

A magnitude 7.1 earthquake struck north of Anchorage, Alaska, on November 30, 2018, at 8:29 a.m. local time (17:29:28 UTC).

www.usgs.gov

ADOT must've been pissed.

 

[Glitch]

ADOT must've been pissed.

It is just part of the job. Fixing pot-holes, frost-heaves, and fissures cause by earthquakes. They have gotten very good at it as well. All the damage to the roads in the photos above were repaired and being used by regular traffic within 72 hours. It was fortunate that no bridges collapsed, or it would have taken a great deal longer.