We all have either experienced the violent shaking of the earth’s surface or have watched them on news. The term for these violent shakings is “earthquake”. Everyone remembers the damage an earthquake caused in Japan in 2011 and the Tsunami that followed. But Japan is a very recent example, there have been many instances in history of massive earthquakes taking thousands of lives.
After knowing the damage earthquakes can cause, you must be wondering how does an earthquake occur? What is the mechanism behind it? Where does it get its energy? We will discuss answers to these questions in the subsequent sections and end our discussion with ways to survive an earthquake.
What causes an earthquake?
The most simple answer to how earthquakes occur is when two blocks of earth slip over one another, it results in an earthquake. The interface where they slip over is called a fault. A fault is a fracture or a zone of multiple fractures between two blocks of rock.
The location where an earthquake starts below the earth surface is the hypocenter. And, the location on the surface of the earth, directly above the hypocenter, is the epicenter.
The layers of earth
The earth has four layers, namely crust, mantle, outer core and inner core. Earthquakes originate in the crust or upper mantle. The structure formed by the crust and upper mantle is in multiple pieces. We know these pieces as the tectonic plates. There are a total of seven major tectonic plates that cover nearly 95% of the earth’s surface. These tectonic plates are in continuous motion sliding past or bumping into one another.
It is the boundaries of these plates that contains many faults. Edges of tectonic plates are rough while the rest of the surface is smooth. So they get stuck at the edges and the rest of the plate keeps moving. When the plate has moved far enough, edges separate from one another on the faults and results in an earthquake.
What are seismic waves?
Since the edges are stuck together, the energy that would have been used to slide the blocks past one another is stored. And, when the plates finally unstick at the fault, this stored energy is released in the form of seismic waves. Seismic waves radiate in all the directions from the fault like a ripple in a pond. When they finally reach the earth surface, they shake the ground and any object on it.
How do we measure an earthquake?
We record earthquakes using a seismograph. A seismogram is data that we get from a recording on the seismograph. The numerical value of the magnitude of an earthquake is measured on the Richter Scale. The Richter scale is a logarithmic scale that measures the magnitude from the log of the amplitude of waves recorded on the seismograph.
An earthquake is generally followed by aftershocks. Aftershocks are smaller earthquakes that occur afterwards the mainshock i.e. the largest earthquake. Sometimes, there are foreshocks preceding the mainshock. Both aftershocks and foreshocks occur in the same place as the mainshock.
How to survive an earthquake?
Things to do before an earthquake
Do mock drills with your family and co-workers.
Always make an emergency plan beforehand about how to communicate during the emergency, choose a place to meet if you are separated from one another. A supply kit is also necessary. It should contain food and water for several days, a flashlight, medicines, a whistle, means of communication and other necessary.
Make your home safe enough to survive an earthquake. You can do necessary changes to any structural defects, secure heavy items that may fall during an earthquake such as TV, refrigerators, almirahs, etc.
How to stay safe during an earthquake
If you are driving then pull over and stop.
Stay away from buildings and any big structure that may fall.
If you are inside a building, stay and do not run outside. Try to avoid doorways.
Drop down on your knees, no matter where you are.
Cover your neck and head with your arms. If you find a desk or a well-built table, crawl slowly underneath it. If there is nothing to crawl under, crawl to an interior wall. But stay away from windows. Hold on to the table you are underneath or the seat you are seated on and be ready to move with it if it moves.
How to stay safe after an earthquake
Be ready to drop, cover and hold in case of aftershocks.
If you are in a building that is damaged, then go outside and stay away from it and any other damaged buildings.
If you are trapped in a building, try to send a message via text, banging on a sonorous object such as pipes.
If you are near the seashore, go inland and higher away from the shore immediately after the shaking stops.
If you are hurt then seek help. If you have training then help others.
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