A common (dip-slip) fault is an lean fracture where the rock mass above one inclined fault moves down (Public domain.)

What is an earthquake?

An earthquake is what happens once two block of the planet suddenly slip previous one another. The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake start is dubbed the hypocenter, and the location directly over it ~ above the surface of the earth is referred to as the epicenter.

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Sometimes one earthquake has foreshocks. This are smaller sized earthquakes that occur in the same place as the larger earthquake the follows. Scientists can’t tell the an earthquake is a foreshock until the bigger earthquake happens. The largest, main earthquake is dubbed the mainshock. Mainshocks constantly have aftershocks that follow. This are smaller earthquakes that occur afterwards in the same location as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and also even year after the mainshock!


A streamlined cartoon the the crust (brown), mantle (orange), and core (liquid in irradiate gray, hard in dark gray) that the earth. (Public domain.)

What causes earthquakes and where carry out they happen?

The planet has four major layers: the inner core, outer core, mantle and crust. The crust and also the height of the mantle consist of a thin skin top top the surface of our planet.

But this skin is no all in one item – that is made up of countless pieces favor a puzzle extending the surface of the earth. Not only that, but these puzzle pieces keep slowly moving around, sliding past one another and also bumping into each other. We speak to these puzzle pieces tectonic plates, and the edge of the bowl are dubbed the plate boundaries. The plate borders are consisted of of many faults, and most the the earthquakes about the human being occur on these faults. Due to the fact that the edges of the plates are rough, they acquire stuck while the rest of the key keeps moving. Finally, once the plate has moved much enough, the edges unstick on among the faults and there is one earthquake.


The tectonic plates divide the Earth"s crust into distinct "plates" the are always slowly moving. Earthquakes are concentrated along these plate boundaries. (Public domain.)

Why walk the earth shake once there is one earthquake?

While the edge of faults space stuck together, and the remainder of the block is moving, the power that would normally cause the block to slide past one one more is gift stored up. When the pressure of the relocating blocks lastly overcomes the friction of the jagged edges of the fault and it unsticks, all that stored up energy is released. The power radiates exterior from the error in every directions in the form of seismic waves like ripples top top a pond. The seismic waves shake the earth as they relocate through it, and when the tide reach the earth surface, lock shake the ground and also anything top top it, favor our houses and also us!

How room earthquakes recorded?


The cartoon map out of the seismograph shows just how the insrument shakes with the earth below it, yet the recording maker remains stationary (instead of the other method around). (Public domain.)

Earthquakes are videotaped by instruments called seismographs. The record they do is referred to as a seismogram. The seismograph has a base that sets firmly in the ground, and also a hefty weight the hangs free. As soon as an earthquake causes the ground to shake, the base of the seismograph shakes too, however the hanging load does not. Instead the spring or string the it is hanging from absorbs all the movement. The difference in position in between the shaking part of the seismograph and also the motionless component is what is recorded.

How carry out scientists measure the size of earthquakes?

The dimension of one earthquake depends on the dimension of the fault and also the quantity of slip on the fault, but that’s no something scientists can simply measure with a measuring tape due to the fact that faults are numerous kilometers deep in ~ the earth’s surface. So exactly how do they measure up an earthquake? They use the seismogram recordings do on the seismographs at the surface of the planet to recognize how huge the earthquake was (figure 5). A short wiggly line that doesn’t wiggle an extremely much method a small earthquake, and a long wiggly line that wiggles a lot way a large earthquake. The length of the wiggle relies on the dimension of the fault, and the dimension of the wiggle relies on the quantity of slip.

The size of the earthquake is dubbed its magnitude. There is one magnitude because that each earthquake. Scientists also talk about theintensity of shaking indigenous an earthquake, and also this varies depending on where friend are during the earthquake.


How deserve to scientists tell where the earthquake happened?

Seismograms come in handy because that locating earthquakes too, and being able to watch the P wave and the S wave is important. You learned how P & S waves each shake the ground in various ways as they travel with it. P waves are additionally faster 보다 S waves, and also this fact is what enables us to tell wherein an earthquake was. Come understand just how this works, let’s compare P and also S tide to lightning and thunder. Irradiate travels much faster than sound, so during a thunderstorm girlfriend will very first see the lightning and then you will certainly hear the thunder. If you are close come the lightning, the thunder will certainly boom best after the lightning, but if you are far away native the lightning, you can count numerous seconds prior to you listen the thunder. The more you space from the storm, the much longer it will certainly take in between the lightning and the thunder.

P waves are like the lightning, and also S waves are favor the thunder. The p waves take trip faster and shake the ground whereby you are first. Then the S tide follow and also shake the floor also. If you are close come the earthquake, the P and also S wave will come one right after the other, but if friend are far away, there will certainly be more time in between the two.


P tide alternately compress and stretch the crustal product parallel to the direction they are propagating. S Waves cause the crustal material to move earlier and soon perpendicular come the direction they room travelling. (Public domain.)

By looking at the lot of time between the P and S wave on a seismogram recorded on a seismograph, scientists have the right to tell how much away the earthquake was from the location. However, they can’t tell in what direction from the seismograph the earthquake was, just how much away it was. If they attract a circle on a map roughly the station where the radius of the one is the identified distance to the earthquake, they understand the earthquake lies what on the circle. Yet where?

Scientists then usage a an approach called triangulation to determine precisely where the earthquake to be (see picture below). The is dubbed triangulation because a triangle has actually three sides, and also it takes 3 seismographs to locate an earthquake. If you draw a circle on a map roughly three various seismographs wherein the radius of each is the distance from that station to the earthquake, the intersection the those 3 circles is the epicenter!

Can researchers predict earthquakes?

No, and it is unlikely they will ever be able to predict them. Scientists have tried countless different ways of predicting earthquakes, yet none have been successful. ~ above any particular fault, scientists recognize there will certainly be an additional earthquake at some time in the future, however they have no way of telling as soon as it will happen.

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Is there such a point as earthquake weather? have the right to some animals or civilization tell when an earthquake is about to hit?

These room two questions that execute not yet have actually definite answers. If weather does affect earthquake occurrence, or if some animals or civilization can tell as soon as an earthquake is coming, we do not yet understand exactly how it works.

Triangulation can be provided to situate an earthquake. The seismometers are shown as green dots. The calculated distance from every seismometer to the earthquake is displayed as a circle. The ar where every the circles intersect is the location of the earthquake epicenter. (Public domain.)