What Should I Know about Earthquakes

How are structures designed to withstand earthquakes?

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To design structures that can withstand earthquakes, engineers must understand the stresses caused by shaking. To this end, scientists and engineers place instruments in structures and nearby on the ground to measure how the structures respond during an earthquake to the motion of the ground beneath. Every time a strong earthquake occurs, the new information gathered enables engineers to refine and improve structural designs and building codes.

What affects how the ground shakes in an earthquake?

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Magnitude is a measurement of the energy produced by an earthquake and is not a measure of the shaking you feel. What you feel is very complex — hard or gentle, long or short, jerky or rolling — and is not describable with one number. Aspects of the motion are described by the velocity (how fast the ground is moving), acceleration (how quickly the speed of the ground is changing), the frequency (seismic waves vibrate at different frequencies just like sound waves), and the duration (how long the

How are earthquakes located and measured?

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Knowing how fast seismic waves travel through the earth, seismologists can calculate the time when the earthquake occurred and its location by comparing the times when shaking was recorded at several stations. Earthquakes are recorded by a seismic network. Each seismic station in the network measures the movement of the ground at that site.

How are earthquakes and faults studied?

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There are many methods used by earth scientists to study earthquakes. For example, surface features that have been broken and offset by the movement of faults are used to determine how fast the faults move and thus how often earthquakes are likely to occur.

What is a fault?

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A fault is a thin zone of crushed rock separating blocks of the earth's crust. When an earthquake occurs on one of these faults, the rock on one side of the fault slips with respect to the other. Faults can be centimeters to thousands of kilometers (fractions of an inch to thousands of miles) long. The fault surface can be vertical, horizontal, or at some angle to the surface of the earth. Faults can extend deep into the earth and may or may not extend up to the earth's surface.

What is an earthquake?

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An earthquake is caused by a sudden slip on a fault, much like what happens when you snap your fingers. Before the snap, you push your fingers together and sideways. Because you are pushing them together, friction keeps them from moving to the side. When you push sideways hard enough to overcome this friction, your fingers move suddenly, releasing energy in the form of sound waves that set the air vibrating and travel from your hand to your ear, where you hear the snap.

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