Earthquakes can literally shake our world, but not in a good way. It is one of the scariest natural calamities that could happen and it can even come without warning. The best thing we could do, at least for now, is to understand more how these tremors occur and in turn, be prepared for what to do if it actually happens.
In the ancient times, when little was known about how the world works, the Greeks believed Poseidon, the Earth Shaker, moved the grounds and toppled over cities whenever he is displeased. Unfortunately, Greece is located in one of the world’s most earthquake-prone areas that the Greeks may have thought their god was often upset about them.
We have come a long way since then. While we might not yet completely understand all the phenomenon that occur to Mother Nature, an accurate understanding of how an earthquake happens has been achieved. Still, the mechanism is complex and laced with many factors contributing to it that researchers continue to put their heads together to gather more details about it.
The Constantly Active Earth
Most earthquakes are caused by natural tectonic processes including the crusts’ movements, shifts, and faults. There are 500,000 quakes happening every year since the ground is always active. In fact, the plates (sections where Earth’s lithosphere is cracked) move in a couple of millimeters each year which is about the same speed of how fast our fingernails grow.
However, only 5 percent of these tremors can be felt with 1 percent of it causing damage. With that, the vast majority of these quakes across the globe happening each year go unnoticed while some of the large ones leave with destructions of properties and loss of lives.
What Causes Earthquakes?
The trembling of the Earth’s surface reminds us that the interior of the land where we are living is still cooling. But this activity does not just happen all of a sudden. They are formed after the following occurs within Earth’s crust:
- Friction stops the rocks from falling into the fault line.
- The energy gets stored up.
- Tension builds up until it reaches a critical point where friction is overcome.
- Plates make a sharp move.
- The stored energy is released which results to the shaking of the ground.
Earthquakes are caused by the sudden release of energy in the lithosphere (Earth’s crust) from a large build-up of pressure within it that creates seismic waves causing the shaking of Earth’s surface. Most of the time, the pressure release occurs in the position referred to as the “focus.”
The focus is also known as hypocenter, the earthquake’s point of origin below the surface. Directly above it is the epicenter which is found on the Earth’s surface that receives the greatest damage in most cases.
Meanwhile, the surface on where the focus slips is called the fault or fault plane. Furthermore, there are three main types of faults: the normal, reverse, and strike-slip.
Plate Boundaries With Many Faults
Tectonic plates are the puzzle pieces that are moving around on the Earth’s surface as mentioned above. Their edges, called plate boundaries, contain a lot of faults where earthquakes usually occur which has various types.
Basically, because the edges of plates are rough, they get stuck when the plates are moving. We then feel the tremors when they finally move far enough and get unstuck. Meanwhile, these are the three types of plate boundaries:
First, there is the convergent boundary where plates move towards one another. When two plates clash, the impact could result to the buckling of one edge or, in some cases, both edges to form a rugged mountain range. At times, the other plate could be bent down into the deep seafloor trench.
The second type is called the divergent boundary where plates move away from each other as magma pushes the plates apart. Oceanic crust made of basalt is created in these boundaries as magma, which rises from the mantle, solidifies into basalt on the ocean floor.
Lastly, the plates that move sideways from each other are found in the transform boundary. The movement of plates here creates a linear fault valley or an undersea canyon but unlike the previous two boundaries, no magma is formed here.
The Pacific Ring of Fire
One of the factors that move the Earth’s surface is volcanoes. The Ring of Fire, sometimes called as the circum-Pacific belt, is a major area found in the basin of the Pacific Ocean where volcanic eruptions and earthquakes always occur.
There are 452 volcanoes found in the ring of fire. Ninety percent of the world’s earthquakes occur in this area including 81 percent of the largest tremors. As a direct result of plate tectonics, the Ring of Fire has indeed hosted the world’s largest earthquakes in the 20th century.
How Quakes Are Recorded
In order to record earthquakes, scientists use instruments called seismographs. Through the data, called seismograms, from this machine, the seismologist can figure out the size of the earthquake and where it happened.
The earthquake’s size called magnitude will depend on the size of the fault and the amount of the fault’s slip that is measured through the collected seismogram. The recordings will show wiggly lines that determine the earthquake’s size based on the wiggle’s length (size of the fault) and size (amount of slip).
Feeling Earth’s Tremors and Its Shocks
The intensity of the shaking will vary on one’s location as per where the earthquake happened. The following are various kinds of waves that are felt differently:
- Body Waves – waves that travel through Earth’s interior and are faster than surface waves
- Primary waves – the fastest kind of seismic wave that can go through solids (granite mountains) and liquids (magma, oceans)
- Secondary waves – the second wave felt during an earthquake that can only move through solids
- Surface waves – waves that have lower frequency and can only travel through the crust but is also presumed to be the most destructive seismic wave
- Love waves – fastest surface wave that moves back and forth, and side to side at the same time
- Rayleigh waves – the wave that moves through rolls moving the ground up and down and side to side like ocean waves
Meanwhile, we can also notice smaller earthquakes before and after the main “event.” Foreshocks are felt in the same place before the “mainshock” or the main and strongest earthquake happens. In some cases, aftershocks can also take place which, depending on the size of the mainshock, could continue for weeks, months and even years.
Events Unfolding After The Earthquake
Sometimes, the terror of an earthquake does not end when the ground stops moving. Following the shaking, ground rupture transpires as the surface of the Earth can be seen visibly breaking. This is extremely dangerous as dams, bridges and nuclear power stations could be destroyed, therefore these kinds of infrastructures critically require careful mapping in areas that are not prone to ground rupture.
Fires and floods are also some of the effects resulting from the shaking of the ground. There is also the instance of landslides and avalanches because of slope instability.
Another one of people’s greatest fears following an earthquake is the tsunami. When an earthquake takes place in the sea, long-wavelength and long-period sea waves are produced due to the abrupt movement of large volumes of water. These large waves could travel from open oceans to far coastal areas in only a few hours after an earthquake.
But above all, the loss of lives is the most catastrophic aftermath of this natural disaster. A domino-effect of calamities could happen in a span of minutes. People can die from accidents of the calamity while those who are injured could not be tended especially when roads are broken and electricity is cut off.
Can Earthquakes be Predicted?
There is a branch of science seismology concerned with the probabilistic assessment of earthquake hazards called earthquake forecasting. It gives estimates on the possibility that a certain area with well-understood faults can be ruptured over a few years or decades.
Another science seismology branch, where earthquake forecasting sometimes falls under, is called earthquake prediction. This will be focused on the prediction of the time, magnitude, and location of an earthquake in the future within stated limitations.
Meanwhile, there are also earthquake warning systems to caution the forecasting and prediction branches when there is a detection of an earthquake. Regional notification of a substantial earthquake could be provided in real-time to areas that might be affected as the tremor progresses.
However, that is all there is – estimates and probabilities. There is no way to actually predict an earthquake despite the efforts of many scientists to create one. While seismologists can be alerted of a potential earthquake in the future, knowing the exact time and specific location remains unexistent.
While earthquakes may signal destruction in today’s human world, they ironically have been part of Earth’s evolution that created our mountains and oceans. This natural calamity is one of our planet’s geological forces that cannot be avoided. Therefore, the best protection against these quakes is really preparedness.