# Earthquakes

We could describe an earthquake as when energy is released causing a movement of the ground. So there are several causes for this.

We could describe an earthquake as when energy is released causing a movement of the ground. So there are several causes for this. One is sudden slippage along faults. Another is crustal plate boundaries. And the third is mid-oceanic seafloor spreading zones.

Mini-test: EARTHQUAKES

Question 1: Earthquakes occur when a release of energy in the earth’s crust cause
A.
B.
C.
D.
Question 2: Once the elastic limit of rocks is passed, they break and move along
A.
B.
C.
D.

[divider]The following transcript is provided for your convenience.[divider]

So basically what happens is we have accumulated stress between plates. Another word for accumulated stress is potential energy. And so we have this potential energy from plate tectonic movements. This potential energy is released as kinetic energy. So if you think about a rock sitting on top of a cliff, it has potential energy because it’s not exerting any energy right now, but it has the potential to have a lot of energy is someone pushed it; because then, it would have energy of it moving down, plummeting to the ground. Now after that rock has been pushed; and it is moving, it now has kinetic energy.

So potential energy is the potential to have energy or the accumulated energy; whereas kinetic energy is more energy in motion. When this potential energy is released, it releases kinetic energy. The effect of that release of kinetic energy is for the ground to shift and for an earthquake to occur. So you can think of it this way. We have these faults and they’re moving up next to each other and it causes stresses along those fault lines. But the problem is there’s friction. So there has to be enough stress to overcome the friction in order for an earthquake to occur.

So think about if I had a box, and the box was sitting on the ground. Say, I just look at the box. The box isn’t moving, and I’m not exerting any stress on the box. There’s no stress on the box. Then say I start barely exerting force on the box. The box still isn’t moving, but now there’s stress accumulating on the box. And the reason the box isn’t moving is because there’s friction between the box and the ground. So eventually, if I keep pushing and I push harder, the force of me pushing will be able to overcome the friction between the box and the ground. In other words, if I put enough stress on the box, the stress overcomes the friction.

So you can see the difference here is that first if I just look at the box or I just barely push the box, both times the box isn’t moving; but one time stress is accumulating. So eventually when there’s enough accumulated stress or potential energy, it releases kinetic energy and the box or in this case, the ground shifts; and then an earthquake occurs. Now earthquakes can also be caused by volcanic activity, massive landslides, nuclear explosions, and other events.