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Old 03-24-2016, 06:40 AM
 
Location: Sherman Oaks, CA
6,565 posts, read 16,482,569 times
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Perma Bear, look up videos on You Tube of tsunamis, especially Japan 2011 and the Indian Ocean 2004. The waves were so big and relentless, I'm not sure an artificial anything would have really protected the harbors. The footage is pretty incredible (and scary!).

Life is all about managing risk, and we make choices about the risks we're willing to take. I'd rather take my chances with an earthquake here in southern California than move to a place that is threatened by hurricanes, tornadoes, or snow and ice storms.

A tsunami threat is pretty easily dealt with. You have an emergency bag packed, and if there is a tsunami warning, you leave and immediately head to higher ground. The good news is that if Japan is hit with another 9+ earthquake, the tsunami will take hours to cross the Pacific Ocean and you'll have plenty of time to evacuate. If the earthquake is local, assuming your house is still standing, just leave as soon as the shaking stops. I wouldn't wait for sirens to go off; what if they were damaged by the earthquake? I'd also go a little further inland than the tsunami inundation map suggests, because it's always better to be safe than sorry.
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Old 03-24-2016, 11:30 AM
 
Location: McKinleyville, California
6,413 posts, read 9,791,565 times
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Quote:
Originally Posted by Perma Bear View Post
Can't they built an artificial peninsula to shield crescent city?
After the 64 tsunami a jetty system was built and it now generates a churning wave that enters the harbor. Crescent City has been hit by 38 tsunamis in the past 78 years, the topography of the ocean floor off the harbor contributes to its vulnerability. A fix would be to build a removable cofferdam to keep waves from entering the harbor. The tsunami is 2011 destroyed the harbor and nearly 40 boats.

An intra plate quake on the Gorda plate off the coast could be as high as the 8's, we wont feel it much here on the coast. In 2005 there was a 7.2 just 90 miles off shore from Crescent City, we felt it here in the Eureka area, but it did not feel like a 7.2 for us, just a bit of a shake. But an intra plate quake can cause a major mud slide on the shelf off shore and that could cause a large displacement of sediment, resulting in a tsunami. Those could generate a freakishly large and local wave of heights as high as 50 feet or more hitting just an area of the coastline. A full rip of the cascade subduction zone from Cape Mendocino to British Columbia causes the entire subduction zone that has been stuck to give way and part of the zone dives beneath the continental crust, which has also been stuck and like a rubber band, snaps back. It is called rebound. Some parts of the coast have been stuck on the diving plate and going down, they rebound and rise back up. All of the coast from Shelter Cove up to Canada is along this diving plate and are fractured into various blocks of North America. A full blown rip would cause a series of tsunami waves that would hit the entire Pacific with waves in Japan to nearly 20 feet and local waves to 30 feet or higher. We would all feel that quake from Los Angeles to Canada and inland to Denver hanging objects would rattle for the entire 4 minutes or more. The Gorda plate is like a rug being shoved beneath the edge of another rug with a crumple zone, the coastal mountains the result and the diving plate at its depth the Volcanoes inland from Mt. Lassen into Canada.


The 1992 Petrolia quakes were subduction quakes, largest a 7.2 not far from Shelter Cove, did major damage to Ferndale. It generated a small tsunami that was not noticed in Shelter Cove, partly because the entire coastline had risen nearly 4 feet from just south of Shelter Cove to Ferndale, and inland about 7 miles it tipped downwards, sort of like a big titter totter with the Kings Range on one side and the Eel River on the other. All of the Pacific north west coast is riddled with faults related to the subduction zone, they are not all strike slip faults, usually they are scarp faults where one plate rises and another falls. In a full blown cascadia earthquake, much of the coast from Humboldt county up to Canada could look like Anchorage with fractured plates of land broken apart. 30 years ago we barely knew that the subduction zone existed and had limited knowledge of even the volcano about 70 miles off shore from Crescent City. 40 years ago most books show the San Andreas fault continuing north from Shelter Cove and off coast tentatively to Canada. But the more we came to know about plate tectonics, we knew those volcanoes would not exist without a subduction zone. Just like in Alaska or in Sumatra, a long subduction zone and a long line of volcanoes related to it.

https://www.google.com/search?q=casc...SYhDz8QiR4IjAE
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Old 03-24-2016, 11:42 AM
 
Location: McKinleyville, California
6,413 posts, read 9,791,565 times
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Quote:
Originally Posted by SandyCo View Post
Perma Bear, look up videos on You Tube of tsunamis, especially Japan 2011 and the Indian Ocean 2004. The waves were so big and relentless, I'm not sure an artificial anything would have really protected the harbors. The footage is pretty incredible (and scary!).

Life is all about managing risk, and we make choices about the risks we're willing to take. I'd rather take my chances with an earthquake here in southern California than move to a place that is threatened by hurricanes, tornadoes, or snow and ice storms.

A tsunami threat is pretty easily dealt with. You have an emergency bag packed, and if there is a tsunami warning, you leave and immediately head to higher ground. The good news is that if Japan is hit with another 9+ earthquake, the tsunami will take hours to cross the Pacific Ocean and you'll have plenty of time to evacuate. If the earthquake is local, assuming your house is still standing, just leave as soon as the shaking stops. I wouldn't wait for sirens to go off; what if they were damaged by the earthquake? I'd also go a little further inland than the tsunami inundation map suggests, because it's always better to be safe than sorry.
I have gone on Google Earth to check out all the elevations in my town, fortunately everything is up hill from us if we head east from the coast and in less than half a mile we are at 120 feet, we are at 60 feet and I would not feel comfortable waiting to see if the waves hit us. For all I would not know, our land could be as much as 20 feet lower or 20 feet higher after a mega thrust quake. We are on a block of land that has a large scarp about 40 feet above ocean line and beyond us to the east is another one about 40 feet higher and another above it. I am trying to get my neighbors involved in conversations on our vulnerability to waves here and the presence of these fracture zones, many of them are self deluded into thinking they are strike slip zones when in reality they are up/down fracture zones between plates of land. I see these zones from here in McKinleyville all the way south to Fortuna. There is even Native tribe legends on how Indian Island in the bay off Eureka showed up after a huge shaking of the land. what it was was one of the plates of land tipping in a mega thrust quake. Geological evidence shows that the bay was not always in existence, that after multitudes of quakes, the seaward side of the land tipped upward and the land side dipped down, creating the bay.
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Old 03-24-2016, 01:36 PM
 
Location: Silicon Valley
18,817 posts, read 28,040,848 times
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Quote:
Originally Posted by TheDragonslayer View Post
I am trying to get my neighbors involved in conversations on our vulnerability to waves here and the presence of these fracture zones, many of them are self deluded into thinking they are strike slip zones when in reality they are up/down fracture zones between plates of land.
What good would a conversation like this be? They may not be deluded, but just don't want to focus on some giant event that may never happen. And if it ever did happen, what could they do about it now? Their land is where it is. You can't change the fracture zones, right?

I think the main point of the thread is that some people are okay with the risk, and others never would be.

The info you shared was really interesting, though.
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Old 03-24-2016, 02:02 PM
 
Location: McKinleyville, California
6,413 posts, read 9,791,565 times
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Quote:
Originally Posted by NoMoreSnowForMe View Post
What good would a conversation like this be? They may not be deluded, but just don't want to focus on some giant event that may never happen. And if it ever did happen, what could they do about it now? Their land is where it is. You can't change the fracture zones, right?

I think the main point of the thread is that some people are okay with the risk, and others never would be.

The info you shared was really interesting, though.
No, I really have neighbors that are deluded into thinking that because there are no tsunami zone signs in their neighborhood, that they are safe, yet just down the block from me is a sign saying on one side, entering tsunami zone and the flip side, exiting tsunami zone, a huge block of the area I live in is as much as 20 feet lower than those signs. I have asked them if they are aware of the potential, and most say they have not even heard of the subduction zone off the coast. How can they know to escape inland, if they do not even know that they should? I am at 65 feet above sea level, not enough as far as I am concerned and my level of knowledge on earthquakes and geology tells me so. I and many did not know about the cascadia subduction zones potential for a mega quake and huge tsunami when I moved here 16 years ago, I would not have bought a property below 100 feet knowing what I know now. I had seen all of these fault scarps since I moved here in 1992, did not equate them with scarps from fractured plates, but started reading about them, thinking of them as ordinary strike slip faults. Now I see them as they are, broken plates of land riding on top of a thrust zone.
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Old 03-24-2016, 08:59 PM
 
Location: McKinleyville, California
6,413 posts, read 9,791,565 times
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I saw this video today on Facebooks Humboldt Tsunami page. It shows how a subduction zone works.


https://www.youtube.com/watch?v=Wt_jJUnTFhg
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Old 03-25-2016, 08:13 AM
 
Location: Sherman Oaks, CA
6,565 posts, read 16,482,569 times
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Dragonslayer, all of your posts are so interesting. Thank you! I love that area of California, but I don't think I'd ever live there. The subduction zone is just one deterrent; the other is lack of good specialists and health care. I'll take an earthquake on the San Andreas or similar strike slip fault rather than a mega thrust earthquake! I was in Joshua Tree (the town) for the Landers earthquake in 1992, and although it was a big earthquake, it was a rolling motion. I was in Glendale for the Northridge quake, and even though I was further away (~20 miles), that motion was more vertical and a lot rougher. That earthquake occurred on a blind thrust fault, which basically means no one knew it was there until it ruptured. The Sylmar quake as on a similar fault.

I was listening to an interview with Lucy Jones (she's retiring from her job as a geologist), and she said you can tell how big an earthquake is by how long the shaking lasts, because the bigger ones last longer. So even if you're far away from the epicenter and the shaking is minimal, count off the seconds. If you keep going past thirty seconds, that earthquake is probably at least a 7.
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Old 03-29-2016, 02:52 PM
 
Location: Caverns measureless to man...
7,495 posts, read 5,653,641 times
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Yeah... roughly 30 seconds for a magnitude 7, a full minute in the mid to high 7s, 2 minutes about an 8, 3 minutes high 8s, and 4 minutes in the 9s. If you're on the beach in much of the Pacific Northwest and you feel a 4+ minute quake, you can pretty much assume that the quake occupied anywhere from a quarter to a third of the remainder of your life.
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Old 03-29-2016, 07:40 PM
 
Location: McKinleyville, California
6,413 posts, read 9,791,565 times
Reputation: 4269
Quote:
Originally Posted by Albert_The_Crocodile View Post
Yeah... roughly 30 seconds for a magnitude 7, a full minute in the mid to high 7s, 2 minutes about an 8, 3 minutes high 8s, and 4 minutes in the 9s. If you're on the beach in much of the Pacific Northwest and you feel a 4+ minute quake, you can pretty much assume that the quake occupied anywhere from a quarter to a third of the remainder of your life.
You are about right, they say the earliest we could get hit is 10 minutes if the quake was not far off shore. Where I live the subduction zone is 40 miles off shore, further south near Shelter Cove is a complicated triple fracture zone consisting of the San Andreas at it northern terminus, the Mendocino fracture zone at its eastern end and the beginning of the Cascadia subduction zone. This coming April 25th and 26th is the 24th anniversary of the Petrolia/Cape Mendocino earthquakes, the first one on the 25th was a 7.2 and was on the south end of the subduction zone, the following two in the upper 6's were intraplate quakes. Shelter Cove got hit by a small tsunami just minutes following the quake and by the next day everyone came to realize that the Lost Coast and Kings Range had been lifted nearly 4 feet and the next winter it was found that the Eel River bed had been tilted downwards. The subducting plate has bunched up the earth along the coastline and inland has snagged the earth and dragged it downwards. If and when that big 9 plus quake hits, all that tension that has built up, is released, much like a bent twig, it trys to snap back, it is called rebound. Earthquake experts tend to believe that the 1992 quake was a precursor to a bigger event on the subduction zone or on the Gorda plate. The San Andreas is trying to tear northward, the Mendocino fracture zone runs all the way to the Hawaiin Islands and the Cascadia subduction zone runs from Shelter Cove clear to British Columbia. The 1906 San Francisco quake ripped the San Andreas all the way to where it hits the triple junction. In the geological timeline of the earth, the time from the last great quake in 1700 that was likely greater than a 9 to the 1906 S F quake is not that long. All these plates and faults are shoving and pushing each other around.
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