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Earth’s crust is made up of vast rock plates in constant motion, grinding against each other as they move. Deep fissures, called faults, separate and occur within the plates. Over time, immense amounts of strain can build up at these faults.
If enough strain builds up, the plates give way. Suddenly, the rocks on either side of a fault can slip past each other, sending all that stored-up energy surging through the ground, resulting in an earthquake.
Seismic Waves
When the rocks at a fault snap and suddenly move, the sudden release of energy produces seismic waves that travel through rock just as waves move through water.
Before an earthquake’s energy reaches the surface, it travels through the ground in two types of waves:
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First, fast-moving P (primary) waves compress and expand the earth in the direction that they travel, the way a spring compresses and expands.
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Next, slower moving S (secondary) waves shake the earth at right angles to the direction that they travel, like a spring shaking up-and-down. |
Scientists have developed many different models and methods for monitoring seismic activity and calculating the probability of earthquakes.
Continue to Predicting Earthquakes? >>
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