4 anni di rilevazioni sismiche sul piccolo lago di Yellowstone

27/04/2013 1677

Da 4 anni dei sensori sismici rilevano l'azione delle onde sul piccolo lago di Yellowstone

L'installazione di potenti sensori sismici nel Parco Nazionale di Yellowstone nel corso degli ultimi quattro anni per tenere traccia dormire vulcano della zona ha fornito una serie interessante di informazioni.

"E 'molto emozionante", ha detto Karen Luttrell, un geofisico Geological Survey statunitense, "Ed è sorprendente quanto abbiamo rilevato nello Yellowstone".

Segue articolo da fonte:  http://missoulian.com/

The installation of powerful seismic sensors in Yellowstone National Park over the past four years to track the area’s sleeping volcano has incidentally provided insight into rhythmic wave events on Yellowstone Lake.

“It’s pretty exciting,” said Karen Luttrell, a U.S. Geological Survey research geophysicist based in Menlo Park, Calif., who co-authored a paper on the seiche waves – pronounced saysh. “It’s a little surprising we detected it at all.”

In Yellowstone, the sensitive sensors were picking up the wave pattern up to 19 miles away from the lake. The reason the seismic sensors were detecting the lake waves is that the waves were displacing so much water within the lake that the weight of the water was actually deforming the thinner Earth crust over the volcano’s caldera, propagating the wave through the Earth’s molten layer, located about 2 to 4 miles below, to the delicate sensors miles away.

“So the crust kind of bends to get out of the way,” Luttrell said.

The deformation is very small, only 1 to 2 nano strains – equal to about 1 or 2 microns over a distance of 2 kilometers. There are 25,400 microns in 1 inch. And the moon and sun daily cause strains of about 50 nano strains because of their gravitational pull.

“So this is a really small deformation,” Luttrell said.

The waves on the lake are equally small, rising only about an inch or two tall over the course of an hour and a half. But it may take a few days for the waves to dissipate.

“You wouldn’t notice this if you were out fishing in a boat,” she said.

But the waves are wide and displace a sizeable amount of water between the lake’s large basins. Water has been detected sloshing between the lake’s West Thumb and Southeast Arm at an interval of about 78 minutes. It also moves between the Southeast Arm and north end of the lake near Fishing Bridge at a rate of about every 51 minutes.

“So even if it’s not very high, it’s a pretty big mass,” Luttrell said.

By employing her calculator, Luttrell estimated that a 10 centimeter Yellowstone Lake seiche weighs about 5 million tons.

“Remember, water is heavy: 1 cubic meter of water weighs approximately 1 ton,” she wrote in an email. “After a little Googling, we figured out that’s the same as 45 Nimitz class aircraft carriers. However, it turns out that the U.S. only has 10 aircraft carriers. So I did a little more Googling, and figured out that the entire U.S. Navy (ships, airplanes and servicemen) weighs approximately 4.75 million tons.”


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