Earthquake

[El and Bill]

Any of you Brats feel the 5.9 quake 112 miles off the coast of Brookings (and depth 6 miles) this morning? It was on the East Pacific Rise, where two major tectonic plates are spreading apart -- the eastern plate is 'scrunching' under the continent along the Oregon Coast (quakes at that collision zone are often larger, shallower, more damaging, and more prone to cause tsunamis).

Quakes at the spreading center are usually not so bad, but there have been some massive exceptions to that statement.

[SeaSpray]

Hi Bill,

From what I can find on the web it was basically an non-event for residents.

I know that over the years that area has had many earthquakes that have been felt. Last year there was a wave that came into Crescent City marina and broke some docks loose and caused some damage after a quake.

Steve

[TyBoo]

We didn't feel a thing on the north OR coast. One of these days, though.....

[El and Bill]

Thought we'd repost this info we put up on the Brat site some years ago. Those of you living in the PacNW might know all this, but we'd hate to lose any friends from the pub when perhaps they aren't aware of this hazard(particularly) along the west coast from Crescent City, CA to AK:

As one of the site's resident geologists, I simply must make some comments about tsunami. Could there be tsunamis on our cruising coasts? The geological answer is YES! And, not only could happen, but has happened many times in the geologic past along the Atlantic, Pacific and Gulf coasts. They are rare along any one shore, in spans of human lifetimes, but possible.

Along the California coast, the Pacific plate is grinding northwesterly beside the western edge of the America's plate, which itself is moving westerly about as fast as your fingernail is growing. The San Andreas is the most obvious of these major faults, side-slipping along the plate boundaries. Ordinarily, side-slipping (or lateral) faults rarely generate tsunamis, although they are famous for major temblors. However, the tsunami in the Indian Ocean was generated by fault slippage along a zone of strong lateral motion. Could a major quake in CA generate a tsunami? Definitely, and most likely from the subsea "landslides," generated by the earthquake, creating large oceanic waves.

Along the Oregon/Washington coast, the Juan de Fuca plate is grinding its way easterly, shoving itself under the westerly moving Americas plate. This is a head-on collision between plates, and the type most often associated with tsunamis. Large tsunamis have drowned the coastlines of these states in recent geologic time, and small tsunamis in the memories of some C-Brats who have grown up on these coasts.

Alaska is seismically active and has, in this century suffered a number of tsunamis, the most recent in Lituya Bay where an earthquake caused the collapse of a mountain into the Bay, generating massive waves.

Our (and Canada's) entire Pacific coast could suffer tsunamis generated as far away as Japan -- Hawaii has been nailed by such events.

The East Coast has in recent geologic times had tsunamis hundreds of feet high, with water flooding inland hundreds of miles across the coastal plain from New York to Florida. These tsunamis were likely generated by earthquakes, and subsequent landslides, in the Canary and Azore Islands.

The Gulf Coast is less likely to suffer tsunami, but earthquakes generated along the island arcs of the Caribbean could cause a seismic wave.

A tsunami travels at hundreds of miles an hour across deep ocean, and may be no more than a foot or two high – virtually undistinguished from normal ocean waves. But the energy incorporated in that speed is transformed into building a lofty wave when the tsunami is slowed by friction against the shallowing sea floor as it approaches land. So, a distant earthquake may, and does, have a devastating effect within a few hours of an earthquake thousands of miles from your shore. Hence, warning time is reduced and only those areas that have an in-place set of sirens, clearly marked tsunami escape routes, and an informed populace have a chance to escape the waves.

What about us on the coast or on our boats? Be aware, that any major earthquake with a near-shore or submarine epicenter can generate a tsunami. If you live on a coast, know the best route inland. And, most importantly, three simple bits of knowledge that might have saved thousands of lives last week:

1. As the seismic sea wave approaches a coast, and builds to lofty heights, the sea will withdraw from the shore! To build the wave, water flows out from land and in from sea. If you are near the shore or on the beach, and suddenly the water level begins to drop (obviously not just the normal tide drop), git outa there. Head up hill as fast as your car or feet can carry you. Many of victims run to the shore – in curiosity or to pick up the flopping fish in what had been a bay. Some are even securing their boats. Most are then swept away by the tsunami.

2. If you are on your boat, say fishing just off shore, and you either hear the alert about a tsunami’s imminent approach or see the sudden lowering of sea level along the shore, head immediately to deep water. That will be outside the wave-buildup zone and be safe. Those along the Gulf, and large areas of the Atlantic coast, won’t have this option since shallow water may extend well offshore down the continental shelf. But, in New England, and most all the west coast, you can in our C-Dorys get into water thousands of feet deep in short order by simply heading seaward at top speed. Some tourists were saved last week when their fishing trips departed just before the tsunami and they were already in deep water.

3. Tsunamis come in multiples! The first wave is seldom the largest, and there may be significant time (hours) between the arrival of waves. The second and third are usually the largest (by far) and a sequence of waves may be a dozen or more. Many of the dead, from tsunamis, survive the first wave, run back to the shore to look for survivors, and are swept away themselves by the following larger waves.

Sorry to be so lengthy, but assume those not interested, would skip ahead and the others who might not have known how to protect themselves and others from tsunamis might benefit.
_________________

[Comfortably Numb]

No skipping ahead here! Not much chance of a tsunami here in Southern Illinois (all bets are off for everyone if otherwise), but this was just fascinating reading. Thanks a lot. I'll keep these things in mind as we visit the coasts.

A long time ago, this region had an earthquake that changed the course of the Mississippi, even causing it to flow backwards for a while. The New Madrid Fault is one of the "meanest" ones around...we have to worry about rumbles a bunch here. A lot of folks here have trouble getting new earthquake insurance policies. Is that an issue on the coasts? Is there such a thing as tsumani insurance?

Sounds silly to ask, but it's slow waiting on the family to get ready to go see Grandma.

[hardee]

El and Bill, Thanks for reposting the tsunami information. Great info for us on the coasts, either on the water or on the shore. Good to know and keep on file in the emergency procedures section.

I'm thinking the original posting was in response to the Thailand disaster. We have a lady who works with us who, along with her family, survived that one. Quit a miracle.

Wonder if NOAA, (or Coast Guard on Ch-16) provides tsunami warnings on the weather channels, like they do for tornado or severe weather. Might be a way to reach folks who are not within ear shot of the sirens.

Harvey
SleepyC

[CatyMae n Steve]

[Salmon Slayer]

Bill,

Lituya Bay indeed experienced a massive Tsunami caused by an earthquake that collapsed a mountainside as you state but it occurred in 1958 and is not the most recent. There have been many since then including the 1964 Good Friday earthquake and Tsunami that killed 106 people in Alaska alone and was deadly as far away as Crescent City California where 8 people died.

I was just a small child when that occurred but I remember my mother being afraid of earthquakes for years after. We physically feel earthquakes several times a year and there are usually several that happen but we dont notice. Thankfully being this far into the inside passage our threat of Tsunamis are almost nil.

Since we have built up all along the coast including places that were literally wiped out in the 1964 quake and Tsunami, the next one will likely be far worse.

[Sneaks]

New Madrid I would be afraid of if I lived anywhere within 500 miles. Been some new research pointing to "anytime now." Otherwise the big fault in CA seems to be east of us here in San Diego. Personally, I think LA is gonna get hammered next....




Don

[SeaSpray]

Here is a question.

I can see that being on the west coast of Vancouver Island could put you in danger for one of these. But, what would happen on the inside? Would large waves lose their energy before getting to the San Jauns or the Gulf Islands? Would Friday Harbor be safe? I would think that Desolation Sound would be a fairly safe place unless there was a local Tsunami.

Would local Tsunami's such as generated on the east side of Vancouver Island be smaller and less dangerous?

Steve

[SeaSpray]

Thought I would bring this up again.

Basiclly I was woundering if you hear a Tsunami warning for the west coast of Washington (comparable to the Thiland tsunami) and you are in the San Juans or Gulf Islands should you run for high ground?

I think it would depend on where you are. On the west side of San Juan Island (Roch and mosquito pass) could be in danger but I am not so sure about Friday harbor or Prevost on Stuart.

Any opinions?

Steve

[thataway]

The NOAA weather site indicates that tsunami warnings are issued on the VHF marine and other NOAA weather channels, plus the all hazard warning is activated on the automatic recievers.

I took my boat to sea in Long Beach several times when there were tsunami wanings. (For example in 1964) Back in the late 40's or early 50's there was some tsunami activity in Long Beach Harbor, we were on my father's boat in the Ceritos channel and there was radical tidal activity.

Bill, good point about the Gulf Coast--Now I have one more thing to worry about--better up my Flood insurance! Even though I live 14 miles from the Gulf, judging from the Storm surges, there would be significant risk--at least of rising water--hopefully not over 12 feet....but...

[DaveS]

[El and Bill]

Steve and Dave --
Some information about the San Juan Islands, and their vulnerability to tsunami:

Indeed, San Juan County is vulnerable to tsunami after a large Cascadia subduction zone earthquake. (This is the major plate boundary lying just off-shore from OR/WA - the Pacific Plate is shoving under our North American Plate generating earthquakes. - bill) Computer modeling completed by the State Department of Natural Resources for the Puget Sound region suggest a maximum wave height on the order of 3 meters, or about 10 feet. This would be higher at the head of an inlet, possibly 20 or more feet. Areas affected by such a surge would be waterfront with low, or no bank. The closer to the high tide level that you are, the more you might be affected by a tsunami.

Geologists believe that if a Tsunami entered our waters through the Juan de Fuca strait it would be no more than 12 feet high. They also believe that a Tsunami from that direction would primarily endanger only the low-lying shorelines on the southwest coasts of San Juan and Lopez Islands, such as the areas around False Bay and Mackaye Harbor. Remember-the Tsunami's height is added to whatever height the tide is.

Also, our islands do not break up a Tsunami. The water has to find a way through, and some of the channels between our islands actually cause the wave to get higher. A computer model shows Bellingham receiving extensive damage after the Tsunamis pass through the San Juans.

They also have a concern for the town of Eastsound if an upthrust quake occurred in the Puget Sound although there have been no studies completed yet on this possibility.

Generally speaking, if your home is above 60 feet elevation, and you are on high-bank waterfront, you should be safe. If your home is on no bank waterfront or on a gentle slope to the water, you need to be prepared for the possibility of a Tsunami.

(Info from San Juan Islander)

[jstates]

Bill and El

Thanks for the information
One local Tribe and clinic south of Aberdeen has taken this seriously and had the state geologists out several times to develop a plan.-


They now have siren, warning system, many alert NOAA radios in the clinic, block captains to empty homes, large number of first responders trained in community, 12 or so new Ham operators, supplies stored in safe area. And they practice the drill where the whole clinic and tribe get up the hill in 15 minutes. "One of The most prepared communities on the WA coast" as I understand. WA state was very helpful in supporting community preparation. They say not if but when - about every 300 to 500 years for last 3000 years just off WA coast - Bill please correct any of this. The theory I was told is the first event is for the Aberdeen coastal area to sink about 6-8 feet - as part of the subduction process - that brings in water - but the big waves follow shortly.

I make a point on the way to work [100 miles] at the above clinic - to note the Tsunami escape routes marked by signs. I have driven the most likely ones so they are no mystery in the dark. Last big Tsunami as I understand here was 1700's recorded in Japan - deposits from the last big one 30' I was told are found all over this area.

There is native legend about the big wave - that
"left canoes [very large carved out cedar logs] in the tops of trees."

I carry combination - LED light /knife /whistle / flint fire starter [Tool Logic] in pocket so I can find my way in dark - headlamp by bed and clothes/shoes readied nearby in one place for escape when I sleep at hotel at water line - on the coast. I tend to think shoes and light are the key elements in the first 30 minutes.

Question for Bill - what do you know about the fault and earthquake risk than runs along the Bremerton - Seattle Ferry route? - what is the likely size / effect in PUget Sound if earthquake occurs here vs the coast -


There are some excellent videos of Tsunamis - will try to find the links another night - - key point about survival from the videos- many that died went back for something material - and were caught by the next wave.


Thanks

Jim