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Earthquakes are caused by movements in the earth’s crust, which is made up of the lithosphere and athenosphere. The movement of tectonic plates triggers earthquakes along plate boundaries and faults. There are three types of faults: slip, thrust, and normal. The intensity of an earthquake is measured on the Richter scale, with most earthquakes being less than 4.5 and at least one greater than 8 occurring every year. The largest modern earthquake ever recorded was in Chile in 1960, measuring 9.5.
An earthquake is a tremor in the earth’s crust, caused by movements beneath its surface. These events can vary widely in intensity, from seismic activity that is barely detectable with sophisticated devices, to devastating earthquakes that can flatten cities and trigger tsunamis and sometimes even volcanic activity. The study of these tremors is known as seismology, a word derived from a Greek word meaning “to shake.”
The Earth’s outer layer, or crust, is made up of two sections: the lithosphere, a Greek word meaning “rocky sphere,” and the athenosphere, a thick layer of liquid that rests atop the upper mantle. The liquid rock of the upper mantle keeps the crust in constant motion, with the edges of the continental plates slowly being pulled apart or brought together as they float on the atenosphere. 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 by the movement of tectonic plates.
There are different types of faults, but most can be divided into three categories: slip faults, thrust faults and normal faults. A slip fault occurs in an area where two plates slide past each other, while a thrust fault occurs when plates are pushed together. A normal failure is the result of the plates detaching. The world’s largest normal faults are found along the deep oceanic ridges of the Pacific and Atlantic where the plates are separating, crashing into the continental plates and causing thrust faulting. The earthquakes along each fault have different characteristics that help seismologists identify them.
The roots of an earthquake are found in the stresses placed on the lithosphere as it moves across the surface of the Earth. Pressure builds along a fault line, which eventually fails, often deep beneath the earth’s crust, in an area called a fire. The corresponding point on the planet’s surface is called the epicenter, and the greatest concentration of damage usually occurs here. When the fault fails, it triggers seismic waves, very low-frequency sound waves that come in different shapes and that can cause the earth to ripple, lift, warp, or tear apart. Waves can continue for hours after an earthquake is triggered, and aftershocks, other smaller aftershocks, can continue for months and possibly even years afterward.
The intensity of an earthquake is called its magnitude. Various scales were proposed to measure this factor until 1935 when the Richter scale was developed. Below this scale, each order of magnitude is 10 times more intense than the last. An earthquake measuring a 2 on the Richter scale is 10 times more intense than a 1, while a 3 is 100 times greater. Most earthquakes worldwide are less than 4.5, the magnitude at which they can start damaging buildings, and there is at least one greater than 8 every year, with the largest modern earthquake ever recorded in Chile in 1960 ; he measured a 9.5.
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