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We all have a general idea about what are Earthquakes. However, we don’t fully get how they work and why they happen. For many people earthquakes in seemingly odd locations like Haiti overthrew what common knowledge they had about them. So as a refresher let’s go over earthquakes and what causes them.
An earthquake is essentially a tremor caused by two pieces of the earth’s crust sliding suddenly against each other. The movement can be minute but the sharp movement release an astounding amount of energy that would even put a nuclear bomb to shame. This shockwave cause the trembling and bucking of the earth that is associated with them.
So what causes an earthquake? The answer lies in plate tectonics. The Earth’s Crust is not one single shell like the one on an egg. It is actually more like the cracked shell of a hardboiled egg. It has major and minor fractures that separate it’s into regions called plates. These plates don’t sit still. They float on a deeper layer of the earth that is called the mantle. The mantle is largely composed of highly fluid melted rock. This ocean of magma has currents just like the normal ocean and these currents moves the plates in a phenomenon called plate tectonics.
Over time tectonic plates will separate and crash into each other creating visible boundaries called faults. When plates collided the enormous masses are locked into each other giving us in part the answer of what happens when the unstoppable force meets the immovable object. They stay locked until one force beats the other. Tectonic plates stay locked until pressure builds up until one of the plates gives and is submerged. This process takes eons and most of the time we don’t notice it. However, among major faults there are points of stress where the pressure is greatest. When these points give and slide past each other they create earthquakes.
Earthquakes can happen on both land and sea so long as there is a major fault line. One interesting fact is that a fault line doesn’t have to be consistently active. In some cases a fault may go years with out triggering. This is what happened with the Port Au Prince Earthquake. A fault line that was not noticed triggered producing a powerful quake that wiped out the capital city of Haiti.
Earth quakes are classified by seismologists using a scale of magnitudes called the Richter scale. This scale ranges from 1 to 10. In living memory there has not been a 10.0 earthquake. Scientist hypothesize they were probably more common in prehistoric times especially as the result of meteor impacts. An interesting fact is that earthquakes happen all over the earth everyday, but most of them are too weak to be noticed.
We’ve also recorded related episodes of Astronomy Cast about Plate Tectonics. Listen here, Episode 142: Plate Tectonics.