What is an Earthquake?
Experiencing earthquakes has been a very frightening encounter for many of us. When you feel earth’s shaking, your only wish is for it to stop and not do more damage to many. Aside from being horrified by the experience, the after effects of earthquake is something that is very alarming just like the occurrence of tsunamis. You hear of appalling stories how one place can be brought to devastation in a snap because of earthquakes. But regardless how we hope that it won’t happen again, the occurrence of earthquakes is something that we are not in control of. It can happen anytime and hit places lying within the fault lines.
Earthquakes are among the many natural calamities that have caused devastation to properties and claimed thousands of lives over the years. In fact, according to statistics, 50 to 80 earthquakes occur every single day and about 2000 each year. When an earthquake occurs, it’s difficult to tell the amount of destruction it would cause in its wake. Apart from devastating properties and buildings, earthquakes can trigger tsunami that can uproot populations or lead to loss of lives. Earthquakes kill many people because they have no warning signs and find people unprepared. Despite efforts by governments to educate the masses on earthquake warning signs and preparedness, a lot has not been accomplished.
An earthquake is an announced or sudden tremor of the earth due to movements within the earth’s crust or volcanic eruptions. To understand earthquakes better, let’s look at how they build up.
What Causes Earthquakes?
The earth’s crust is composed of solid core, mantle (consists of molten magma) and tectonic plates. Tectonic plates are constantly moving due to convection currents triggered by molten lava inside the earth crust. This constant movement leads to either the plates sliding against each other or drifting away from each other. These interactions and drifting apart of tectonic plates underneath the earth are perceived by living organisms, humans included.
The constant movements have even led to the formation of mountains and valleys. When these plates move against each other, there is a point where they interact. In geological terminology, this meeting point is known as fault line. This fault line is sometimes known as fracture in the earth’s crust. The moment the plates begin to move, the potential energy, commonly known as stored energy, is released from the meeting point, known as hypocenter. The outcome is an earthquake.
Tectonic plates found in ocean are called oceanic plates while those found in continents are continental plates. With the movement of these tectonic plates, energy is formed and can be released once these plates meet in the so called fault line. The intensity of this released energy will also determine that of the earthquake. One can feel the earth’s shaking once energy is released from earth’s crust.
In few occasions, earthquakes have foreshocks. Foreshocks are smaller version of earthquakes that occur in the same area as the bigger earthquakes that ensues. Up until now, scientists have not been able to tell whether an earthquake is a foreshock until the real earthquake occurs. The real or larger earthquake is known as the mainshock. Mainshocks, on numerous occasions, are followed by an aftershock. Aftershocks are a collection of small earthquakes that take place after the main earthquake. Depending upon the magnitude of the mainshock, aftershocks may continue to happen for weeks, months or even years.
For earthquakes to occur, energy is released from a focal point. This point is called the epicenter and usually found at shallow depths from the earth’s surface. From the epicenter, seismic waves is produced and sent out to all directions. Seismic waves then travels at varying speed depending on the kind of material they go through.
Types of Earthquakes
The earth’s crust is composed of loose, cracked fragments of lands referred to as tectonic plates. These plates are capable of moving slowly and gradually. The movement of these plates occurs in different forms; towards each other, away from each other, sliding past each other or colliding with each other. A huge tremor occurs when 2 moving tectonic plates slide over one another. This type of earthquake is known as tectonic earthquake. Tectonic earthquakes are the most prevalent kinds of earthquakes in the world. Its magnitude may be small or large. Tectonic earthquakes have caused most of the planet’s mass destruction. Tremors triggered by tectonic earthquakes are always severe, and if their magnitude is high, they are capable of bringing down an entire city in seconds.
Compared to tectonic earthquakes, volcanic earthquakes are less prevalent. They typically take place before or after an eruption. Volcanic earthquakes come in two forms: long-period volcanic earthquakes and volcano-tectonic earthquakes. Volcano-tectonic earthquakes usually happen after a volcanic eruption. During an earthquake, magma erupts from inside the earth’s crust leaving a space behind. The space left after magma eruption must be filled. To fill it, rocks move towards the space resulting in severe earthquakes.
On numerous occasions, magma blocks the vents during a volcanic activity. This means that the high pressure fails to be released. The buildup of pressure becomes unbearable and releases itself with a massive explosion. The massive explosion results in a ruthless earthquake. On the other hand, the long period volcanic earthquake takes place after a volcanic eruption. Some days prior to the massive explosion, the magma inside the earth’s crust experiences rapid changes in heat. The change in heat triggers seismic waves, resulting in an earthquake.
These are caused by nuclear explosions. They are, essentially, man triggered kind of earthquakes and represent the biggest impact of modern day nuclear war. During the 1930s nuclear tests conducted by the United Sates, numerous small towns and villages were devastated as a result of this grave act.
These kinds of earthquakes are generally smaller and most commonly occur near underground mines. They are sometimes referred to as mine bursts. Collapse earthquakes are instigated by the pressure generated within the rocks. This kind of earthquake leads to the collapse of the roof of the mine instigating more tremors. Collapse earthquakes are prevalent in small towns where underground mines are located.
Effects of Earthquakes
- Damage to buildings
High magnitude earthquakes can lead to complete collapse of buildings. Debris from collapsing buildings is the main danger in the course of an earthquake because the falling effects of huge, heavy objects can be deadly to humans. High magnitude earthquakes result in shattering of mirrors and windows, which also present danger to humans.
- Damage to infrastructure
Earthquakes can cause electricity lines to fall. This is dangerous because the exposed live wires can electrocute humans or start fires. Major earthquakes can cause rupturing of roads, gas lines, and water pipelines. Broken gas lines can cause gas to escape. Escaping gas can result in explosion and fires, which may be difficult to contain.
- Landslides and rockslides
When an earthquake occurs, large rocks and sections of earth located uphill can be dislodged, consequently, rolling rapidly down into the valleys. Landslides and rockslides can cause destruction and death to the people living downstream.
- Can result in floods
High magnitude earthquakes can instigate cracking of dam walls, collapsing in the long run. This would send raging waters into nearby areas leading to massive flooding.
- Earthquakes can trigger tsunamis
A tsunami is a series of long high sea tremors sparked by an earthquake or volcanic eruptions under the sea. A tsunami can wipe out an entire surrounding coastal area population. A typical example is the March 11, 2011, earthquake and tsunami that struck the coast of Japan leaving more than 18, 000 people dead in its wake.
- Leads to liquefaction
Liquefaction is a phenomenon where the soil becomes saturated and loses it strength. When sediments consisting of high water content are subjected to constant trembling, water pressure held in the sediment pores slowly increase. Ultimately, the sediments lose almost all cohesive strength and start acting like liquids. Buildings and other structures built on top of this liquefied soil overturn or sink into the ground. Earthquakes are responsible for most of the liquefaction occurring across the world. A typical example of liquefaction phenomenon is the earthquake of 1692 in Jamaica that resulted in the devastation of the town of Port Royal.
How Are Earthquakes Measured
Earthquakes are measured by the amount of force or energy they produced. This done through Richter scale. This tool was developed by Charles F. Richter of the California Institute of Technology. Many times you must have heard or read about this tool in news or internet. Richter scale uses the information produced through seismograph to calculate the magnitude of the earthquake.
Magnitude of an earthquake gives you an idea of the effect of an earthquake. Earthquakes occurring above 7 on Richter scale are known to have much devastating effect and can cause severe damage to life and property. Earthquakes occurring below 3 on Richter scale can’t be felt. Earthquakes occurring between 3 and 6 are said to be of mild type. Countries like Japan are prone to earthquakes as they come in high seismic zone. When an earthquakes occurs in sea, it paves way for Tsunami. One of the most devastating Tsunami occurred in Indian Ocean on Dec. 26th 2004.
Can Earthquakes Be Predicted
Till date, scientists have not been able to predict earthquakes. Many modern techniques have been used, unfortunately none of them has worked. Is any such toll is built to predict earthquakes, many lives could be saved in future.
The only thing that you can do is to educate yourself about earthquake management and be vigilant in times disasters. You can also do precautionary measures by buying properties which are not located in known earthquake-prone areas or fault lines. The occurrence of earthquake can happen anytime and we will never be ready for it and the imminent danger it brings. But with earthquake preparedness measures and awareness, it can make you alert and quick in making sound decisions in times of danger.
References: USGS , HowStuffWorks
Image credit: Angelo
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