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annikam17

Weather Affects Timing Of Some Natural Hazards - Science News - 0 views

www.sciencenews.org/...timing_of_some_natural_hazards

Annika Marshall

shared by annikam17 on 28 Aug 12 - No Cached
  • Seasonal patterns of rainfall and snowfall can affect how often quakes and volcanoes go off, scientists reported December 8 at a meeting of the American Geophysical Union.
  • monsoon storms runs off the mountains
  • weight bends the Earth’s crust slightly
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  • this bending causes the surface to move back and forth
  • Seismic records collected from 1998 to 2004 show that the number of quakes drops in the rainy summer months and rebounds when things dry out.
  • the flexing eases the stress on the fault where two tectonic plates collide beneath the Himalayas.
  • seismicity
  • Positioning System
Annika H

Destroying five myths about earthquakes | The Japan Times Online - 1 views

www.japantimes.co.jp/...eo20110831a3.html

Annika

shared by Annika H on 28 Aug 12 - No Cached
  • 1. Animals sense impending earthquakes. A golden oldie. The notion that animals anticipate impending earthquakes predates the birth of Christ, with documented references to unusual animal behavior as early as the fourth century B.C. This belief was fueled recently by accounts, including one in The Washington Post, that some animals at the National Zoo had their knickers in a knot just before the 5.8 quake.
  • 1. Animals sense impending earthquakes.
  • This notion could contain a kernel of truth: Being generally squat, four-legged, close to the ground and inclined to sit still, an animal might feel an initial weak shaking that goes unnoticed by humans until stronger waves arrive. But also, it is an example of a natural human tendency to look back in time for anomalies, or precursors, that supposedly heralded the coming quake. Every pet owner understands that, say, cats and dogs sometimes behave strangely for no apparent reason; that's what cats and dogs do. And if an earthquake had not subsequently struck, you can bet we would not be talking about strange animal behavior this week — because we wouldn't have noticed anything out of the ordinary. As far as we understand, animals, like humans, have no ability to predict earthquakes.
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  • 2. The frequency of large-scale earthquakes has spiked.
  • Yet the frequency of tremors across the world always fluctuates considerably from year to year. And the energy released by big earthquakes since the end of 2004 was less than the energy released by the two biggest recorded earthquakes: the 1960 temblor in Chile and the 1964 Good Friday quake in Alaska. The number of earthquakes greater than magnitude 7.0 has been somewhat high in recent years but well within the range throughout the 20th century.
  • Yet, as far as we understand, an aftershock of a certain magnitude is no different from an independent temblor of a similar magnitude. The shaking and rupture are the same; the energy released is the same. And aftershocks can be more damaging than larger "main shocks" if they strike closer to population centers. This lesson was illustrated with the earthquake that struck Christchurch, New Zealand, in February — an aftershock of a larger but less-damaging quake that occurred the previous September.
  • If enough stress has built up on a fault to generate a magnitude-7.0 earthquake, say, it would thus take about 1000 earthquakes with a magnitude of 5.0 to release the equivalent energy. The Earth doesn't work that way.
  • In any given area, the numbers of tremors of different magnitudes almost always follow a simple mathematical progression, with about 10 magnitude-6.0 quakes and about 100 magnitude-5.0 quakes for every single magnitude-7.0 quake. Thus, if there is significant strain energy to be released, it must be released in large earthquakes.
  • 4. "Don't worry, it was just an aftershock."
  • 3. Small earthquakes are helpful because they release pressure and prevent larger ones.
  • Recent studies show that any earthquake — even an aftershock — has the same small statistical chance of triggering a larger tremor. So a single quake can potentially be an aftershock and a foreshock, further clouding the differences among them.
  • 5. Earthquakes are a West Coast problem.
  • But, as millions of people on the East Coast were just reminded, less active does not mean inactive. By the end of the 19th century, two of the most notable temblors in the United States were the 1886 quake in Charleston, S.C., and a sequence of large events centered near the boot-heel along the New Madrid Fault of Missouri in 1811-1812.
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