3.)Earthquakes

As the lithospheric plates of the Earth continue their slow motions, stresses build up in the crust, especially near the plate boundaries. Those stresses (compression, tension, shear) build up in the crust until the stress exceeds the strength of the rock or the friction along a preexisting fault. Then, sudden slippage of rock along a fault occurs. The ground shakes as the stress energy is released and the rocks lurch to their new position in a matter of seconds. Seismic waves travel outward from the portion of the fault that broke, like expanding ripples from a pebble dropped in still water.

The whole fault doesn't move at one time; only the part of the fault around which the stress exceeded the strength. Seismologists can determine the point on a fault where the slippage began, the area (length and depth) of the fault that slipped, the amount of slippage or fault throw (how far the crust moved), and the time it took for the slippage to occur. The focus or hypocenter is the exact position on the fault, including the depth, where the slippage began. The epicenter is the map position of the Earthquake. It lies directly over the focus

4.) While the edges of faults are stuck together, and the rest of the block is moving, the energy that would normally cause the blocks to slide past one another is being stored up. When the force of the moving blocks finally overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The energy radiates outward from the fault in all directions in the form of seismic waves like ripples on a pond. The seismic waves shake the earth as they move through it, and when the waves reach the earth’s surface, they shake the ground and anything on it, like our houses and us.

5.) Earthquakes often cause dramatic changes at Earth's surface. In addition to the ground movements, other surface effects include changes in the flow of groundwater, landslides, and mudflows. Earthquakes can do significant damage to buildings, bridges, pipelines, railways, embankments, dams, and other structures.

6.) So scientists rely on seismic waves—shock waves generated by earthquakes and explosions that travel through Earth and across its surface—to reveal the structure of the interior of the planet.An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.