Chandri MacLeod (chandri) wrote,
Chandri MacLeod

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Earthquakes, and why here is a bad place to be if one happens.

The lecture today was basically the same as last semester's in Environmental Science: same Powerpoint, even. Did learn something new, though.

So there are three kinds of tectonic plate boundaries. Transform, Convergent, and Divergent. Transform is where the plates just move past each other (California). They have the least serious quakes, because they have fewer of the kinds of waves (think sound waves in the ground) that cause big damage. Divergent is where the plates are moving apart: that's usually where the cracks happen, 'cause, duh, plates moving apart. Convergent boundaries (like the one off the coast of BC) are where the plates are shoving into one another. These have the worst quakes, when they do have quakes, because they usually also have subduction zones, which is where one plate tilts and slips under the other, usually grinding everything off the top of the plate in the process. They also have practically every kind of seismic wave known to science, because they move the slowest, and the slower waves are more dangerous.

Okay. Anyway. The new thing. Our earthquakes, technically, are worse than California's. At least they would be if we *had* that many. They're potentially worse, anyway. 'Cause of us being on a subduction boundary (where one plate's sliding under another, in this case the Juan de Fuca plate is shoving under the North American Continental plate) whereas Cali's on a transform boundary. Which is why California would never fall into the sea: there's nowhere for it to go. We, on the other hand, would. A little. Well. Richmond/Delta would. *shrug*

Stupid disaster movies always have big cracks opening in the ground and sucking people in, then closing again. Okay, well, first of all, that's stupid: not only does that almost never happen, even at divergent boundaries, but the fractures do not close up again and trap/crush people. Sure, people fall in, but they're more likely to die from the impact at the bottom than by being crushed.

Actually, they're more likely to be crushed by falling buildings. "Earthquakes don't kill people. Buildings kill people."

Apparently the whole joke about fissures opening and swallowing people was started after a quake back in the early 1900s. A farmer found that one of his cows had had a heart attack during the quake and died. He also found that a fracture (just a little one) had opened on his property. He looked at the cow, he looked at the fracture, and since the cow had been dead too long to butcher, he dropped the cow into the fracture and started filling it with dirt.

Along came a city reporter. The reporter saw the fracture, the cow inside, looked at the farmer, all wide-eyed, and asked:

"Did that fracture catch/crush that cow?"

The farmer blinked, looked at the cow, looked at the reporter, and said: "Uh... yes."

So all this crap about fissures opening and sucking people into the ground and closing up again behind them all started because some farmer wanted to screw with the city-folk. ;)

The Richter Scale is funny. Geologists haven't used it for about ten years, because it's kind of inaccurate. But, Brett says: "we gave it to the media. Never give anything to the media."

Know what else is funny? The Modified Mercalli Intensity Scale. It's funny 'cause it's a qualitative, subjective scale based entirely on the level of human panic. It goes from "I: not felt except by a very few under especially favorable circumstances" to "IV: sets off car alarms" to "VII: Everybody runs outdoors." to "VIII: sand volcanoes" to "XI: giant fissures open" and goes from there. It's kind of amusing if you look at it from a scientific perspective. Brett thinks they should modify it to range from "I: everyone picks up the phone and asks 'did you *feel* that?'" to "XII: people stop trying to use the phone because the lines are down from everyone calling to ask 'did you *feel* that?'".

I really need to use the big earthquake at some point in the Paxverse. I even know what parts of the GVRD will be a metre deep in seawater. *nods*

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