The Science Behind Earthquakes

I am certain that you are familiar with the 8.9 magnitude earthquake and tsunami which hit Japan yesterday. In case you do not know too much about earthquakes, and about the way in which they are formed, keep reading.

What are they, and how are they formed?

An earthquake takes place when two blocks of earth slip past one another. The surface where the two plates slip is called the fault plane. The place where the earthquake occurs beneath the earth is called the hypocenter. The epicenter is the place where the earthquake occurs above the earth. When an earthquake occurs, smaller earthquakes usually follow, and they occur in the same place where the first one occurred. These small earthquakes are called aftershocks and they can continue for a very long period of time, sometimes for a year or so. Our planet has four layers: crust, mantle, outer core, and inner core.

The surface of our planer is made out of the crust and a small portion of the mantle. However, underneath the crust and the mantle, there are lots of activities taking place. You see, the interior of the Earth is not full; it is not like a billiard ball. The earth is made out of blocks, or pieces, which are called tectonic plates and these pieces are on a constant motion. They constantly hit each other, and touch each other. The margins of the tectonic plates are called plate boundaries, and these plate boundaries are made out of numerous faults. The majority of the earthquakes occur on the faults. During an earthquake, the edges of the plates touch each other, and they get stuck. However, the other portions of the plate keep on moving. Since the plates are moving, the edges are required to move as well, and when they are pulled and they separate, that is when the earthquake is triggered.

The reason why we feel the earthquake on the surface is because of the energy which has gathered beneath the Earth. Under normal circumstances, when a tectonic plate slides above another plate, the energy is distributed equally. However, when the edges get stuck, the energy is stored, and when the edges finally manage to break free, all the energy which was stored is released all of a sudden. The energy is released in waves. Think about the ripples on a lake when you throw a stone in the water. That is what happens in the earth as well. These waves cause motion in the Earth, and finally when they reach the surface, they cause the ground to move as well. Usually the earthquake do not last too long, they last for seconds, but even so, the damage which they do is very intense.

How are they detected and measured?

The scientists are able to record and to measure the size of the earthquake by using various technologies and devices.  In order to be able to record an earthquake, they need to use a seismograph. This device uses a base and a weight which hangs in the air. When an earthquake occurs, the base moves but the weight stays motionless. The scientists simply have to look at the movement of the base in order to see if an earthquake took place. The size and the slip of the fault are very important when it comes to measuring the earthquakes. In order to measure the intensity of the earthquakes, the scientists use the data recorded by the seismograph. Using that data, they are able to determine the size of the earthquake. Think about the polygraph, the one you have seen in the movies. When it detects a lie, the line on the paper changes from a horizontal motion, to a vertical one. The same thing happens in this case. The bigger the earthquake is, the bigger the line will get. The size of the fault dictates the length of the wiggle, and the amount of slip dictates the size of the wiggle. The earthquakes are measured in magnitudes, and each earthquake has only one magnitude. The earthquake which took place had an 8.9 magnitude, which is very big. The largest earthquake ever so far was 9.5.

The scientists are also able to detect the exact location where the earthquake took place, determining both the epicenter and hypocenter. They use various formulas in order to pinpoint the exact location of the earthquake, but they use the waves caused by the shake in order to solve the problem. Two different types of waves are created after an earthquake, called the P and the S waves. The P waves are faster than the S waves, and the scientists can measure the time between the P and the S waves from a certain location. If the distance between them was very low, then it means that the earthquake was very close. The farther the distance between them is, the farther the earthquake was from that location.

Predictability

Many people have wondered if the earthquakes can be predicted, and the answer is no. In fact, the scientists believe that they will never be able to predict these calamities, as they do not follow a certain regular pattern. They have tried and still try to develop methods of predicting the earthquakes, but they have been unsuccessful at it. However, the scientists are able to tell that there will be an earthquake on a certain fault, but they do not know when it will happen. Many have also said that the weather can affect the development of the earthquake, but that has not been proven. Also, there are theories about the possibility that the animals might be able to detect these phenomenons. That wasn’t proven either.