The location where an earthquake begins is called the epicenter. However, the vibrations from an earthquake can still be felt and detected hundreds, or even thousands of miles away from the epicenter. The energy from an earthquake travels through Earth in vibrations called seismic waves.
Scientists can measure these seismic waves on instruments called seismometer. A seismometer detects seismic waves below the instrument and records them as a series of zig-zags. Scientists can determine the time, location and intensity of an earthquake from the information recorded by a seismometer.
This record also provides information about the rocks the seismic waves traveled through. A seismometer records seismic waves as a series of zig-zags. Scientists have measured quakes on Earth's Moon, and see evidence for seismic activity on Mars, Venus and several moons of Jupiter, too! On Earth, we know that different materials vibrate in different ways. By studying the vibrations from marsquakes, scientists hope to figure out what materials are found on the inside of Mars.
The earth has four major layers: the inner core, outer core, mantle and crust. The crust and the top of the mantle make up a thin skin on the surface of our planet. But this skin is not all in one piece — it is made up of many pieces like a puzzle covering the surface of the earth. Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and bumping into each other.
We call these puzzle pieces tectonic plates , and the edges of the plates are called the plate boundaries. The plate boundaries are made up of many faults, and most of the earthquakes around the world occur on these faults. Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving. Finally, when the plate has moved far enough, the edges unstick on one of the faults and there is an earthquake.
The tectonic plates divide the Earth's crust into distinct "plates" that are always slowly moving. Earthquakes are concentrated along these plate boundaries. 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 cartoon sketch of the seismograph shows how the insrument shakes with the earth below it, but the recording device remains stationary instead of the other way around. Earthquakes are recorded by instruments called seismographs. The recording they make is called a seismogram. The seismograph has a base that sets firmly in the ground, and a heavy weight that hangs free.
When an earthquake causes the ground to shake, the base of the seismograph shakes too, but the hanging weight does not.
Instead the spring or string that it is hanging from absorbs all the movement. The difference in position between the shaking part of the seismograph and the motionless part is what is recorded. So how do they measure an earthquake? They use the seismogram recordings made on the seismographs at the surface of the earth to determine how large the earthquake was figure 5.
The length of the wiggle depends on the size of the fault, and the size of the wiggle depends on the amount of slip. The size of the earthquake is called its magnitude.
There is one magnitude for each earthquake. These waves move only through rock. They move up and down or side to side, perpendicular to the direction in which the wave is moving. Surface waves follow P and S waves.
They travel along the surface of the earth and thus cause the most damage. Surface waves can be characterized as Love waves, which are faster and move the ground from side to side, and Rayleigh waves, which roll like waves on the surface of oceans and lakes.
What other types of earthquakes exist? In addition to tectonic earthquakes, seismologists have classified three more earthquake types: Volcanic : Earthquakes that occur in conjunction with volcanic activity Collapse: Smaller-scale earthquakes that result from the subterranean collapse of caverns or mines Explosion: Earthquakes caused by underground explosions of nuclear or chemical devices.
Does fracking cause earthquakes? Image Lightbox.
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