hey there!  welcome to the new episode of Curiosity! A series in which we will answer some of the questions that makes us all curious.

The ground beneath you starts shaking, walls cracks, and soon everything collapses in an blink of an eye. Most of us might have experienced earthquake and we know it's very deadly. In fact, The ground beneath our feet is always moving, but very very slowly. We cant't feel the ground moving most of the time. But , when we finally feel it, it known as Earthquake. But , how does this deadly force originate taking thousands of lives? Well, this is what we are gonna discuss today. without a further a do , let's get started.

Firstly, What's an Earthquake?

Earthquakes are simply the vibrations generated by the massive rocks under tremendous stress. The surface along which these massive rocks moves is known as "Fault Plane" creating seismic waves. The size of an earthquake can range from very weak, which might not even be felt sometimes to very strong destroying the whole cities.

What Actually Causes Earthquakes?

Earthquakes are may be the result of a natural or even human activities. Human activities that produces seismic waves such as mine blasts and Nuclear tests. Also , the natural causes might be , massive landslides, Volcanic eruptions, massive rock slides and most importantly by Tectonics plates. 

Earthquake due to Tectonics Plates

This is probably the most common cause of the largest earthquakes that have ever occurred. If we look at the cross section of the Earth, we will see the different layers of the Earth, namely crust(surface), mantle, outer core and lastly inner core. Mantle has got the largest volume of them all and contains molten rocks but ocean and all the other land masses lies on the Earth's Crust. Our Earth's Crust is not a One Solid piece instead it is divided in to number of pieces forming different sections known as "Tectonic Plates".

Fig: All the Tectonic Plates (Credits)

These plates are always in motion(very slowly) due to the fact that, they lie over mantel. Mantel contain molten rocks with the thick syrup like consistency making it constantly in motion. These different plates moves relative to each other. The speed of most of the tectonic plates can be 1-3 cm per year. However some plates move very fast with the speed of 2 inches per year. The places where the tectonic plates meets are known as "fault". There are solid rocks above the fault line. These solid rocks helps in keeping both sides of the fault line together i.e two tectonic plates. But these two tectonics plates are still moving and put the massive pressure on the solid rock, When the stress on the solid rock reaches out of limit, the rock suddenly breaks releasing massive amount of energy causing Earthquake.

Also , another reason for earthquake is , when two rock slide against each other, they sometimes get stuck. They don't slide for some time but still the plates are still pushing against one another. After some time, there's already massive amount of pressure built up causing to break the rocks holding them up and creates massive energy causing Earthquake. After the earthquake these plates starts moving again very slowly, until they get stuck together again in the future.

Fig: Movement of plates (Credits)

The place right under the Ground where the Rock breaks producing earthquake is known as "Focus" and the place just above the Focus is known as "Epicenter".

[2] Earthquake due to Volcanic Eruptions

When a volcano erupts, it triggers an earthquake but because of a totally different reason. When the eruption occurs the molten rocks moves towards the ground through the small chambers. The magma breaks out with a massive force but it totally depends on how large the volcano is. The amount of the magma and the temperature of the magma directly under the ground causes the ground to tremble. 

We can take Krakatoa Event as an example. The volcanic eruption of the Krakatoa was so massive that it blew the whole island apart and the explosion was heard up to 4000 miles triggering massive earthquake and tsunamis destroying nearby islands completely.

How do we measure the Magnitude of an Earthquake?

All of the earthquakes are measured by a special tool known as "Seismometer ". It's a very precise machine that collects all the vibrations from an ongoing earthquake and print it out on a seismograph. The Seismograph consist of X, Y and Z axis. X and Y axis are frequently plotted in the graph but Z axis mostly remains absent until a massive Earthquake hits. The seismograph has a base that is attached to the ground and the heavy weight hangs above the graph. when ever an earthquake occurs, the seismograph's base moves but the hanging heavy weight doesn't move, the spring absorbs all the movement, this leads to record all the shaking and motion part of the Earthquake.

Fig: Seismometer (Credits)

There is not just a single seismometer ,in fact there is a network of seismometer. When an earthquakes hits, the magnitude is recorded by each of these seismometer and distance form them is also recorded. If there is one unit increase in magnitude , the ground motion increases by ten times. This means the magnitude 5 earthquake is 10 times greater than magnitude 4 earthquake and 100 times greater than magnitude 3 earthquake.

 That's it for this Episode guys, Hope you enjoyed it. If you did, Upvote and comment your thoughts below. Thank you

Stay Curious.

---

References Used:

[1]-https://earthquake.usgs.gov

[2]-http://www.geo.mtu.edu

[3]-http://www.ga.gov.au

Last Five Episodes: 

Curiosity | What causes Auroras ? The Northern Lights

Curiosity | Is Telekinesis Possible?

Curiosity | How does Caffeine Keep you awake?

Curiosity | Can a Volcano Wipe out Humanity?

Curiosity | Is time Travel Really Possible?