It seems like an earthquake happens somewhere every day. Scientists are trying to learn how to predict them and to understand what causes them. Now Maya Tolstoy of the Lamont-Doherty Earth Observatory of Columbia University says ocean tides may be the basic cause of earthquakes, including those on dry land.

Cracks on the ocean floor cracks take in water and spit it back out, as the tides rise and fall. Tolstoy found that earthquakes occurred at an underwater volcano in the Pacific Ocean when the tides were at their lowest point and pressure was reduced on the volcano. The tides pump water in and out of cracks in the volcano, building up, then reducing pressure. Reduced pressure at low tide means the cracks can pump in more water.

So underwater earthquakes are caused by the tides?but how can they cause earthquakes on land, which are the ones we worry about? The reduction in pressure at low tide reduces the downward force that holds rocks in place along earthquake faults. This allows the faults to move which is what produces an earthquake. This slippage may originate in the ocean, but the effect eventually moves along the fault until it reaches land, and that?s when we?re effected. When scientists spot an underwater earthquake in the ocean, they find it usually produces an earthquake on land about 2 hours later.

Since low tide happens every day, any fault that stretches from the ocean onto the land will be effected daily. If you live in an earthquake fault zone, you?ve got a daily chance of experiencing what in LA they call ?The Big One.?

Earthquakes have been destroying civilizations since before written history, but they?ve always coped and come back. Barbara Hand Clow explains how disasters make us stronger in ?Catastrophobia, now in the sale section of our store,click here.

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