Many faults and a few mostly modest quakes have long been known around New York City, but the research casts them in a new light. The scientists say the insight comes from sophisticated analysis of past quakes, plus 34 years of new data on tremors, most of them perceptible only by modern seismic instruments. The evidence charts unseen but potentially powerful structures whose layout and dynamics are only now coming clearer, say the scientists. [snip] The researchers found concrete evidence for one significant previously unknown structure: an active seismic zone running at least 25 miles from Stamford, Conn., to the Hudson Valley town of Peekskill, N.Y., where it passes less than a mile north of the Indian Point nuclear power plant. The Stamford-Peekskill line stands out sharply on the researchers' earthquake map, with small events clustered along its length, and to its immediate southwest.
Unless you're a fan of disaster flicks, "New York City" and "earthquake" probably don't occur to you in the same sentence frequently. But the Earth is full o' faults. They pop up in rather surprising places, like the center of the United States, and do astonishing things, like make the Mississippi River flow backwards for a time. Seriously, it happened.
When we think of earthquakes, I think most of us think of the devastation. We don't really think so much about what earthquakes are telling us about how our world works. And we don't think about their landscaping skills. They're really fascinating things, especially if you don't have to worry much about being hit by one.
Let's have a look at where that's likely to be.
If you know anything about plate tectonics, you're noticing a pattern about now: earthquakes mark out the boundaries of the plates pretty well. And the types of earthquakes tell us a lot about the type of boundary we're seeing. For instance, shallow-depth, low-intensity earthquakes occur at mid-ocean ridges, while areas demonstrating a continuum of shallow, intermediate or deep quakes - a Wadati-Benioff zone - shows us we've got a subduction zone.
Earthquakes have taught us things as diverse as what the interior of the world might look like and whether some absolute bastard's exploded a nuclear bomb on the sly. That's because you can learn a lot from a seismic wave. Different types of waves travel differently depending on what caused them and what they're traveling through:
The mechanical properties of the rocks that seismic waves travel through quickly organize the waves into two types. Compressional waves, also known as primary or P waves, travel fastest, at speeds between 1.5 and 8 kilometers per second in the Earth's crust. Shear waves, also known as secondary or S waves, travel more slowly, usually at 60% to 70% of the speed of P waves.
P waves shake the ground in the direction they are propagating, while S waves shake perpendicularly or transverse to the direction of propagation.
All of this is fascinating and informative stuff, but it may not have a personal meaning for you. Unless you live in volcano country, that is. If that's the case, harmonic tremors become your dearest friends. Harmonic tremors alert scientists to the movement of magma beneath a volcano, and a swarm of them lets you know that it's maybe kinda sorta time to run like hell.
This is good information to have when you live next to a volcano.Earthquakes don't just destroy and warn: they sculpt. Some pretty amazing landscapes have been created by them.
On our left, we have a canyon in Jordan created by water eroding an earthquake fissure.
And to our right, an earthquake fissure in California that, with enough time and running water, could become a rather spectacular gorge.
Here's Earthquake Lake in Montana, created one day in 1959 when an earthquake triggered a landslide that formed a natural dam. Bet you the beavers were jealous.
I hope this whirlwind tour of earthquakes has given you at least some sense that they do far more than just make things shake and knock cities down. They're pretty fantastic things, quite useful, and even wonderful. As long as you don't have to meet one in person... good luck on that, New York.