Seattle Earthquake

They said that the earthquake started 30 miles underneath Seattle. What is down there and what did it do?
Is there a well-known techtonic plate at that level, and was it parting or closing? 2) What is an epicenter? I looked it up and it says it is the center, but why call it epi, which means around? In other words why do they say the epicenter of an earthquake was at such and such a place if they meant the center? 3) If there is an earthquake, doesn’t the wave go around the globe and peak at the antipodes, thus causing a shock there, and then come bouncing back to produce another but weaker earthquake?

  1. Try these links for your general quetions:

  1. Not sure.

  2. No. Eartquakes only have so much energy (some more than others, obviously). They don’t have magic powers to send shocks around the world. As the shock wave moves through the earth, it bleeds off energy until it all dissipates.

(1) This Tectonic Plate Map shows the Juan De Fuca Plate and the North American Plate meeting near the coast of the American Northwest. Here you can see some topographic images of the spreading boundary between those two plates. I’m not sure of the relationship between the offshore plate boundary and the region that produced this particular quake… maybe someone else can fill in that gap. Just in case it helps, here’s the USGS hazard map for the area.

(2) I’m not sure why the epi- prefix is added to center when discussing the center of an earthquake. Maybe because the center can only be approximately determined?

(3) IIRC, the waves do go around the globe, but they get weaker and weaker the farther they travel, dissipating the force that caused the original earthquake, so by the time they reach the antipodes, they no longer contain sufficient energy to cause an earthquake. The Exploratorium page contains a good explanation of how earthquake waves are transmitted through the Earth.

Merriam-Webster says of the epicenter:

So the epicenter is not the center, it is the point on the Earths surface near the center.

What you have in the PNW is a convergent plate boundary; the Juan de Fuca plate is subducting beneath the North American plate. The subducting plate will go quite some distance beneath the overriding plate before it becomes hot enough to melt and be incorporated back into the mantle. Therefore, you have a plate scraping along on the bottom of another plate for a long way, causing all sorts of nasty things like earthquakes and volcanoes (the Cascades). The earthquakes tend to have a deeper focus the farther away from the plate boundary you are–draw a picture and you’ll see why this is.

Be grateful it was just an earthquake and not another exploding mountain like Mt. St. Helens–the Cascades are “andesitic” volcanoes, which refers to the type of magma they erupt. Andesite is an igneous rock of a composition a lot higher in silica than basalt, which is the rock type you find in Hawaiian volcanoes. Andesite is much more viscous than basalt due to this higher silica content and gives you much more violent eruptions than basaltic volcanoes.

The point directly above the center, to be more precise.

Another term to remember: hypocenter. This is the point under the surface where the earthquake actually happens, where those plates are actually moving and making contact.

What are the chances of Mt. Rainier erupting like Mt. St. Helens?

This site:

says that it is unknown when or if Mt. Rainier will erupt again. However, “a huge lahar - a fast-flowing river of mud, rocks and water - could cascade off the mountain with little if any warning.” This would be catastrophic for the thousands of people living nearby.

According to the Cascades Volcano Observatory:

Sounds like the risk is low, at least for now. Though if Rainier did blow, that would be very, very bad.

I happen to live at a university approximately 15 miles from said epicenter of said earthquake. This also means that I happen to be directly in the path of an eruption of said Mt. Rainier. As such, I am informed on a very regular basis, by amateurish geology students, that Mt. Rainier is long (read: a millenium) overdue for an eruption. I didn’t put much stock into that until my oceanography professor confirmed it. I still choose to disbelieve it though. Call it sheer hopefullness/stupidity. Not that there is a whole lot I could do even if I did believe it.

On a related note, our university does not, however, lie inside the path of a long past lahar or pyroclastic flow (don’t know which). So apparently, if Mt. Rainier were to spew anything, we might be safe. But again, this is all second hand info I’ve received from geology students who may not have any real grasp on what the professor is trying to tell them.

I don’t know about you all, but if I was living anywhere even close to something like a volcano, or in a place likely to have a large-scale earthquake sometime soon, I might consider moving my ass way the hell outta there.

But who am I to say? Maybe being consumed by highly-caustic burning ash and lava, or being dashed to pieces by falling debris, or even being swallowed up by the earth could turn out to be fun!
If any of you have that happen, be sure to come back and tell us how it was.

Did natives ever actually worship volcanos or the volcano god, as depicted in movies? I think Dorothy Lamour and possibly Hedy Lamarr and the beautiful actress who played Lily Munster may have been in these films. Also,wasn’t Hanuwele the Hawaiian Volcano Goddess?
t Hanuwele

But, it might not happen any time soon - or even in my lifetime - so it isn’t really something I worry about.

I feel the same about people in tornado country or along the southern east coast … where the hurricanes are coming. They will be there. They happen at least once a year. Why on earth are people still living there? Why do they keep going back disaster after disaster?

Yeah, but it might happen tomorrow…
Frankly, I’d prefer not to be there when it does, that’s all.
You might be right. It may not happen in your lifetime… But it is sure to happen in someone else’s.

Where you at SINsApple, Pacific Lutheran University? Of all the Universities in the Puget Sound region, I can think of none in the path of a rapidly moving mud flow from an erupting Mt. Rainier, you should be just fine.

Enumclaw, Orting, Puyallup… look out guys, you have maybe 20 minutes of warning prior to a less than relaxing mud bath courtesy of Mt. Rainier.

If it blows, it blows. St. Helens, slugs, and rain will never conquer us, neither will the Mountain of Rainier!

Consider the wonders of Geography, us Washingtonians are now 4 centimeters closer to Canada :slight_smile: Cool eh?

Re Mt. Rainier: As was discussed in some of the various Red Cross disaster preparedness trainings I’ve attended, Mt. Rainier is considered one of the worst (as in Top Ten) potential geological catastrophes waiting to happen. Huge volcano, proximity to large population centers, add to this the number of glaciers on the mountain that feed major rivers that will turn into gigantic mudslides rushing down toward most of the area’s biggest cities…

Stupendous man, where do you live?

Did you know that the most deadly natural phenomenon is heat? More Americans have been killed by extreme heat (or its side-effects of water and food shortages) than by earthquakes or any other weather phenomena. We can’t all live where it never gets extremely hot. The only places I can think of are all on the West Coast, where there are the aforementioned earthquakes and volcanoes. The rest of the country gets extremely cold in the winter.

All you can do is pick the natural phenomenon you’re willing and able to endure.