Earthquake

For planning purposes what constitutes "deep water"?

My front yard is the eastern portion of the Strait of Juan de Fuca and is home to a number of "Banks" where the bulk of the water is 25 fathoms or less deep. Even the main channel westward which appears to be a marine "canyon" is seldom more than 500 feet deep.

Sequim Bay is just a puddle+ deep.

Is any of this sufficient volume of water to limit the surface effects to waves less than 10 or 12 feet or so?

Paul Priest
Sequim
 
The C-Brat on Comfortably Numb wrote that there was little chance of a tsunami in Illinois -- and that is surely correct -- but there is a threat, in Illinois, from the earthquake itself. There was one this morning.

A quick summary of the geology of the area. This region is not on a present-day plate boundary (where earthquakes usually occur, such as the boundaries near the west coast). BUT, this WAS a plate boundary long ago (a rifting, or pull-apart, boundary) and so is still seismically active. There were huge quakes located at the southern tip of IL in the past -- the location of today's quake is ne of the huge quake location. A 5.4 quake happened at this current site in '68, and quakes of this magnitude strike at this site every decade or two, and small shakes are felt here once or twice a year. In the recent geologic past, much bigger quakes occurred here.

East of the Rockies a quake is felt over an area ten times larger than a similar magnitude quake in the west. A 5.5 eastern quake can be felt 300 miles away and cause damage in a wider area than in the west. (For instance, there has been a series of quakes in the past month off the OR coast of the same magnitude as this one in IL, and no Brats reported feeling the western quakes).

As the news reports come in, we'll see if there was damage from this quake.

What to do if you feel an earthquake (that could be a precursor of a bigger one, or you may feel the first arriving waves and the bigger one is en route)?

1. Get outside far away from all buildings if there is time. The shaking won't kill you, but a falling facade or wall sure can!

2. If quake catches you inside, get in a doorway or room corner (where ceiling is less likely to fall on you). Cover face and head with arms.

3. If no time to move far, drop to the floor, under a table if that's close.

4. Be away from glass (mirrors, windows) or things that might fall on you, if possible.

5. If in bed, and there's time, get under it. If not, get a pillow over your head.

6. If in a car, stop away from buildings, overpasses, or big trees.

7. After shaking stops, think fire! Could be electrical or gas line damage.

8. If trapped, cover face with something if you can -- if you survive the debris fall, dust often is the biggest danger! Don't shout (might inhale dust) except as last resort - tap tap if you hear rescuer, if you can. If pinned, don't try to move (might dislodge something that will fall on you, or create dust).

Chances are none of you Brats will ever be in this problem -- but forewarned is forearmed!

I've been through a number of quakes (in Vermont and California) -- and the worst, I was outdoors, in central Nevada -- the ground lifted and rolled in visible waves (like one sees from the wake of a boat) several feet high and maybe thirty feet apart -- terrible groaning noise as frozen ground shifted-- mountains in near distance shook like a dog, with rocks rolling down the mountainside leaving trails of dust. Stood with legs far apart to maintain balance (like in the boat hit by a wake). Awesome! And I don't use that word as teenagers do.
 
Bill,

I agree that there will probably not be an Illinois tsunami, but if there is a strong enough shake, there could be some ramifications on the rivers. I believe that the New Madrid earthquake in the early 1800s had rivers running backwards and created new channels and oxbows.

Steve
 
That is a great list to keep in mind. I had not thought about or heard of the danger from dust before.

It seems that we are not sure what type of list like this to make for a case of being in our boats cruising. If we are boating and see a large earthquake happening or hear a NOAA warning of a tsunami what would anyone do?

Getting a tsunami warning on VHF I think would give us a relative time frame. I think the warnings would be "Tsunami expected within 30 min" or "possibility of tsunami in the next 24 hrs" or " take immediate action". We do have the tsunami warning/monitoring system in the pacific.

In the immediate situations if I was within five minutes or so of shore with higher ground I think I would head for that. If more than 30 min. from a safer place I would try to identify the safest place on the water that I could reach quickly ( a lot of subject personal judgment at the time).

Obviously you immediately prepare as best you can for possibly being in the water with or without your boat. Life jackets, warm clothing, water proof VHF, EPIRB, remove camper canvas to make exiting the boat easier, etc.

Any other ideas?

Steve
 
Bill, your advice:

6. If in a car, stop away from buildings, overpasses, or big trees.

is GOOD! I was on Hwy 101 going from San Jose headed northbound when the quake hit in SF Bay area that collapsed (pancaked) the bridge into Oakland -- I felt it first (felt like semis going by and 'wind pushing' my Honda -- but there were NO semis), then saw light poles on the side swaying like palm trees in the wind and then realized it was an earthquake. I pulled to the shoulder, stopped, turned off the engine -- then realized I was really close to an overpass -- restarted my engine, pulled ahead another 100 feet, turned off the engine again -- they tried to tell us the quake only lasted 10 seconds -- I'm not all that speedy...it was still rocking the light poles -- very scary!

Caty
 
I have been at anchor or aboard the boat in a marina during several earth quakes. It feels like a giant shark has taken ahold of the boat and shaking it--even in a 30 ton vessel.

Marie's home in Corinth, Mississippi, was damaged by earthquakes on the New Madrid fault in the past. The situation was compounded by the subdivision being built on ground which not stable, and where there was some water intrusion--and new springs formed in the basement after the quake. Corinth is about 100 miles from St. Louis. We have a farm in central Illinois, where the quake was felt this morning, but not significant damage occured.
 
Standing in a doorway is no longer recommended because door openings are a weak point in the wall and people get crushed there when the wall collapses. Also, a swinging door can cause injury if one is holding onto the door jam. Even standing, itself, is not possible in a severe earthquake.

Taking shelter under a table or bed is also inadvisable in a severe earthquake where catastrophic damage occurs. Many people are crushed to death underneath collapsed tables when heavy debris falls on top of them, whereas there is often an open space right next to the object which is created by the fallen debris. If the person had been there instead, they would have survived. According to rescue workers who have seen many collapsed buildings, one should crouch directly next to a sturdy piece of furniture because there is a chance that falling debris will get propped up against the object, thereby creating an "open triangle of safety". The key to survival is figuring out where these open triangles of safety are likely to occur when a structure collapses. Typically these areas are created directly next to large objects in the center of a room. Just some food for thought; it's all a crapshoot anyway.
 
Some thoughts about safety on a boat, during a tsunami: (and remember, every location is unique and every wave comes from a unique direction so generalities are difficult - know your location!)

VHF Marine radio gives warnings. NOAA weather radio is usually the best choice but CH22Coast Guard will also broadcast if possible. Local radio stations may be helpful.

1. You are in deep water (over 600 fathoms) and you hear the tsunami warning on the VHF:

In deep water you are most likely not in any danger. Tsunamis travel very fast, at low wave height, in deep water. Their energy there is in their speed. You probably won't feel it or be aware of its passing.

Don't return to harbor or marina -- tsunami damage is near shore. Waves often come in sets, so stay at sea until you hear the all clear on the VHF.

2. You are at a marina:

Remember: Tsunamis often are heard near shore -- sounds like a loud roar from a train or plane. This warning is really important at night since you might miss visual signals. If you actually see the wave, you are potentially in immediate danger -- take action quickly!
Don't go in the marina buildings -- they will probably not be safe -- unless multistoried and reinforced concrete (and there's no time to run to safety).

Don't head to sea unless there is plenty of advance warning time (warnings are often hours in advance of the wave if the cause (earthquake, volcanic eruption, meteor impact) is very far away {tsunamis can cross the Pacific Ocean} and deep water is within that time frame. Consider there could be other traffic heading to sea that might slow you down.

If you felt the earthquake that generated the tsunami warning, leave the boat and head to high ground. The wave may be generated too close for you to 'outrun' it by trying to take your boat to deep water.

3. You are on the boat, in shallow water.

The warning gives you sufficient time before predicted wave arrival -- head for marina and then you head for high ground or run boat to deep water to protect you and your boat (your call).

Too little time to move to safety ( you felt the earthquake and then get the VHF tsunami warning or the warning's arrival time gives too little time or you observe unusual tidal actions along the shore (ups and downs) or current shifts at sea (sudden increase or decrease or reversal of current) --

either beach the boat and run fast for high ground or, if not possible --

slow boat, move toward deepest water available, stay alert with hand on throttle, face the expected direction of wave arrival, and be ready to power into the wave as you would any large wave at sea. Like any large wave, it increases height as it 'feels' bottom and approaches shore -- similar to a large swell breaking on the shore. You might be able to power through the approaching wave.

In a channel you will probably not have a breaking wave unless the tsunami is running against a tidal current or strong wind -- it will probably be a mound of water approaching fast and with a strong current behind the wave. You will probably have visual warning of the tsunami approach, since the water near you will rush toward the approaching wave (reversing tidal flow, or increasing its velocity if running with the tide).

In a channel, after the passing of the wave, there will possibly be a 'return wave' as the water piled on shore heads back to sea. This will again give a reversal of the current, so be aware of this possibility by turning your boat, after the wave passing, toward the new current direction.

Remember -- tsunamis come in sets!! The first wave may not be the highest. Be aware that a second, third (or more) wave will soon be arriving and be alert and ready. Getting through the first wave may not be half the battle! Wait for the all clear before heading to marina or dock.

Tsunamis can run up rivers like a tidal bore! You're not necessarily safe if you are near the mouth of a river.

Hope that these ideas (gleaned from many sources) will be helpful for Brats to consider. Forewarned is forearmed! If this site stays around for a few hundred years (remember, I'm a geologist and have a different sense of time than 'normal' folks) -- anyway, if around for a few hundred years, I can guarantee that some of us will have to survive a tsunami. Otherwise, the ideas might only be helpful if you're on the short end of the probablility curve.
 
Good info... one might ponder on the fact that if you where out in the deep, there may not be a port upon your return, arrrg.

I have often wondered what effect a large T. would have on the Columbia and how much damage upriver it would cause. I've found many T. models on the internet but never anything on the river.

A few years back we stayed at a condo at Ocean Shores that is located on the end of a long spit with but one access road. I asked the lady at the desk about tsunamies. She said the all the phones where tied into a computer that would ring your room in the event one should happen. She advised that if it was due to the fault farthest offshore, to grab the best Scotch and head for the top floor, if it was the fault closer to shore, grab the Scotch and head for the beach and get ready for a helluva site. :)
 
On the West coast, we have taken our boats to sea durning warnings everal times, but there the continental shelf drops off very rapidly. On the East Coast and Gulf Coast where the continental shelf is long and shallow, you would have to get much further to sea before you were safe.

There are also Tusanmi type of waves caused by atmospheric pressure and to some degree by tidal changes: The "La Rissaga" at Ciutadella Minorca is often accompanyied by a "roll cloud"--with sudden atmospheric pressure changes, localized Sieches which have been reported in Malta, the Great Lakes and some other areas are also isolated high wave events. We just missed a La Rissaga of about 3 meters height, at Minorca, yet were anchored only 60 miles away at Majorca, in a similar harbor and had no wave or current effect. That wave devistated the fishing boats in Ciutadella and took out most of the quay side buildings.

If we had a major Tusinami on the Gulf coast, I would be affected--since my house is only about 12 feet above sea level--up a large bay. The question is, does a narrow pass, with a 14 mile long bay attenuate the wave? In hurricanes it tends to accentuate the storm surge as a series of constant waves set up a resonate pattern in the upper bay systems, especially where they narrow and shoal.
 
Hi Bill,

A very good list of possible actions and what to expect if you are in the unlucky spot in time and location.

I have lived in California and mostly the SF Bay area for more than 30yrs and have never felt what I consider significant affects from a quake. I have felt many quakes but mostly as just a bump. I live about 40 miles from Oakland and during the last big one I was walking back across the street from the mailbox. I thought I was having trouble reading and walking at the same time - not even any thought of an earthquake. I realized it was a quake after going inside and I saw the lamp swinging.

So for any one of us the chance is very small. But I do feel better having some idea of actions to take. I might not of thought about the rebounding of the waves after you pass over one.

There were a few interesting stories about kayakers around Thailand that survived that tsunami because of their locations and actions. The waves were not as bad as we saw on TV in every location. In some places just a short distance from major damage there was very little damage.

Thanks Bill,

Steve
 
A new swarm of earthquakes under the Salton Sea on the San Andreas fault line gave me cause to bring this thread up front again. 40 quakes, from 4.8 on down since Saturday is giving the talking heads plenty of ammunition. That part of the San Andreas hasn't really moved in over 300 years and it certainly could be a precursor to "The Big One." SeaHawk might yet be able to launch from his back yard....

OAS, for Bill, I watched "How the Earth was made" the "Great Lakes" episode and it amazed me that the ice over that area was over a mile thick at one time and today buildings along some of the lakes are still rising 1" per year as the crust rebounds from that massive weight of long ago.

Don
 
Don -
The recent swarm of earthquakes in the area of the Salton Sea is not unusual - there have been several other periods of intense small-scall activity in the past ten years. This swarm seems concentrated between the southern end of the San Andreas fault and the Imperial fault - two north-south faults and the swarm seems to be mostly on the east-west trending small faults joining the major systems.

Seismologists often think in either of two ways about swarms of little faults:

1. Tis' Good - it is releasing pressure in small shakes rather than allowing the build-up of a big one.

2. Tis' Bad - this is evidence of pressure building up along the fault (or between the fault zones, in this case. The small shakes are precursors to the BIG one and a warning.

Guess we'll sit back and watch - I don't know of any quartz rods that measure pressure across the fault zones in this area - perhaps we'll hear of some. They are the best indication. Twist quartz and it generates piezoelectric energy, read on a meter. Increasing pressure means increasing probability of release with a major earthquake. I'll fall back on the geologist's favorite excuse: Time will tell.
 
Here's the map:

intensity.jpg


And it does indeed show the east end of the Seattle "hot" zone in Fall City and the Snoqualmie Valley. That is sort of the I-90 corridor. We had some damage in our area in the Nisqually earthquake, but in my memory, no buildings have come down!


El and Bill":2f6pmv53 said:
And here's a reference for Pat and Patty -- note the east end seems to start in your backyard!

http://earthquake.usgs.gov/eqcenter/shakemap/pn/shake/seattle_art_se/
Click to expand...
 
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