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1) Post your answers to these questions: What causes earthquakes? Of the following factors, which do you think is the most reliable predictor of earthquakes? Explain your answer please.

(a) recurrence interval
(b) animal behavior
(c) rock precursors

2) Post your answer to this question: Compare the use of the Mercalli scale and the Richter scale to measure the size of an earthquake. What are the advantages and disadvantages of using each scale?

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Question : What causes earthquakes?

Answer : Earthquakes are one of the indicators of increased volcanic activity leading up to an eruption. As magma forces its way up into a volcano, it pushes aside the rocks in its way, causing bulges in the ground and a flurry of earthquakes. Most Earthquakes are caused by Plate Tectonics. The earth's crust consists of a number of sections or plates that float on the molten rock of the mantle. These plates move on convection currents caused by heat rising from the center of the earth. The hot magma rises and spreads out on the surface, creating new crust. The crust spreads out forming a new plate until it meets another plate. One of the plates will be pushed down into the interior of the earth and reabsorbed into the mantle. Plates can also be compressed to push up mountains when they collide or move sideways along transform faults.

The plates are the Earth's crust that float on the molten rock in the center of the Earth. Most of the inside of the Earth is so hot that the rock melts. Just as a pot of hot chocolate on the stove will bubble as it is heated; the molten rock, or magma, very slowly bubbles up in great currents under the surface of the Earth. The crust that floats on the magma moves with it, like the skin that might form on the hot chocolate. The Plates are just pieces of the crust. The part that makes it hard to understand is that it all moves so slowly. Even though the magma is very hot it is also very thick and under tremendous pressure in the middle of the Earth. So it moves only a few centimeters a year. Over millions of years ...