What are Earthquakes?
How Earthquakes Cause Destruction We live on the thin crust of a layered Earth. The crust or surface of our planet is broken into large, irregularly shaped pieces called plates. The plates tend to pull apart or push together slowly, but with great force. Stresses build along edges of the plates until part of the crust suddenly gives way in a violent movement. This shaking of the crust is called an earthquake. The crust breaks along uneven lines called faults. Geologists locate these faults and determine which are active and inactive. This helps identify where the greatest earthquake potential exists. Most faults mapped by geologists, however, are inactive and have no earthquake potential. When the crust moves abruptly, the sudden release of stored force in the crust sends waves of energy radiating outward from the fault. Internal waves quickly form surface waves, and these surface waves cause the ground to shake. Buildings may sway, tilt, or collapse as the surface waves pass. The cons
An earthquake is a tremor in the Earth’s crust, caused by movements below its surface. Earthquakes can vary widely in intensity from seismic activity which is barely detectable using sophisticated devices, to devastating earthquakes which can level cities and trigger tsunamis and sometimes even volcanic activity. The study of earthquakes is known as seismology, a word derived from a Greek word meaning “to shake.” The Earth’s outer layer, or crust, is composed of two sections: the lithosphere, a Greek word meaning “rocky sphere,” and the athenosphere, a thick layer of liquid which rests on top of the upper mantle. The liquid rock of the upper mantle keeps the crust in constant motion, with the edges of continental plates being pulled slowly apart or together as they float on the athenosphere. The movement of these plates is what triggers earthquakes. In addition to plate boundaries, earthquakes also occur along faults, cracks in the lithosphere caused by the stresses created as tectonic
What causes them? Why do earthquakes feel so different from one another? Earthquakes are the Earth’s natural means of releasing stress. When the Earth’s plates move against each other, stress is put on the lithosphere. When this stress is great enough, the lithosphere breaks or shifts. Imagine holding a pencil horizontally. If you were to apply a force to both ends of the pencil by pushing down on them, you would see the pencil bend. After enough force was applied, the pencil would break in the middle, releasing the stress you have put on it. The Earth’s crust acts in the same way. As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy which moves through the Earth in the form of waves, which we feel and call an earthquake.
