Yesterday X31, the wise troll, told us how quakes on the moon happen. Today we're going to talk about earthquakes.
Earthquakes are violent outbursts of tremor in the ground. They can be so intense that buildings may collapse, cracks may open on the ground and even tsunamis may rise from the seas.
(Image source - author, Max Pixel - license)
Yeah, yeah we know all that, but why?
The cause of an earthquake lies in the movement of plate tectonics, the stiff pieces of the puzzle that form the planet's upper layers, above the inner and outer core. Tectonic plates are basically the top layers of the earth, the crust moving over the burning hot, liquid mantle; as they move around slowly over time they may cause three types of earthquakes that occur around the boundaries of the plates, the faults (where two or more plates meet).
- Convergent boundary: When two plates collide and one pushes the other, causing hills and mountains to rise. They happen over a thrust fault.
- Divergent boundary: When plates are separated from each other forming seas and oceans. They happen over a rift zone.
- Transform fault: When plates slip by each other, AKA strike slip.
There can also be intraplate earthquakes, far beyond the plates' boundaries, meaning that the stress coming from a fault can spread farther. Finally, earthquakes can be related to volcanic activity, caused by magma and/or plates' movement.
(Image source - author, Eric Gaba)
Earthquakes are also categorized based on the depth they occur. Therefore we have "shallow-focus" in depths less than 70 km, "mid-focus" or "intermediate-depth" in depths of 70-300 km (where we trace the subduction zone, the area where the sliding of a plate beneath another plate that leads to its melting down by the hot magma happens) and "deep-focus" in depths from 300-700 km.
And what leads to the earth's reaction?
The pressure accumulated due to the plates' moving around must eventually be released and that happens through seismic vibrations. We can detect foreshocks that warn us for the main seismic event and aftershocks that come after the mainshock, which are actually the gradual adjustment of the plates to the new order of things.
How do we measure them?
Special organs called seismographs (greek words everywhere) are used to measure the size of an earthquake. Using a seismogram, scientists can determine the depth, magnitude and epicenter of the earthquake. The most famous magnitude scale was the Richter scale, but it has slowly become obsolete. There are also the "surface wave magnitude scale" (to measure remote earthquakes), "moment magnitude scale" (that considers the amplitude of the shock and the seismic moment which is: the total rupture area, average slip of the fault and rigidity of the rock). And three more that are based on the observed effects: "Japan Meteorological Agency seismic intensity scale", the "Medvedev–Sponheuer–Karnik scale", and the "Mercalli intensity scale" [source].
(Image source - author, Z22 - license)
We must also take into account the different types of waves that are produced during an earthquake. We get the P waves "A P wave is a compressional wave, a seismic body wave that shakes the ground back and forth in the same direction and the opposite direction as the direction the wave is moving" [source]. We also get the S waves "An S wave, or shear wave, is a seismic body wave that shakes the ground back and forth perpendicular to the direction the wave is moving" [source]. P waves travel faster than S waves to reach you, by measuring the time differential between those waves, scientists can determine how far the epicenter was.
What bad things do they cause?
Earthquakes can happen all the time but being weak they are left unnoticed. Intense earthquakes on the other hand can prove disastrous with the most bitter toll being human lives. Collapse of buildings and bridges, cracks in roads, landslides, fires (caused by electric wires or gas lines), soil liquefaction (the ground losing its stiffness and strength), floods (from the rupture of river dams) and tsunamis (from earthquakes that happen below sea surface) are the main side-effects of an earthquake.
Is this the only explanation?
In Greek the earthquake is also known as enceladus (just like one of Saturn's moons). In ancient mythology, Enceladus was one of the Giants who got killed in the great battle between the Giants and the twelve gods of Olympus. One version claims that Athena buried him under Etna or the island of Sicily and as he was trying to move he caused earthquakes. That's why the ancient Greeks worshiped him as the god of earthquakes. If the above scientific approach did not work for you, you can take the alternative my ancestors have to offer :P
(Image source - author, Marie-Lan Nguyen)
Do they happen only on earth?
No, quakes can happen everywhere, the moon (moonquakes), Venus (venusquakes), Mars (marsquakes), the sun (sunquakes) and other stars (starquakes). The mechanisms of each quake vary though.
They are dangerous and scary, how can we protect ourselves?
Since we cannot predict them always, there are several precautions we can take to prevent us from getting hurt.
When an earthquake strikes:
- Get down on all four and protect your head under your arm.
- Find a cover and get under it.
- Stay away from windows and balconies.
- Don't use lifts (as power break downs may occur).
- As soon as the shaking stops, get out the building you're in keeping any available object above your head for protection and get to a safe open space.
On the level of building safety, caution measures should be taken during construction, especially in areas with frequent seismic activity. Moreover, education of the public and coolness in the event of an earthquake can prove life-saving.
An episode of the SciShow will give you a thorough explanation:
References
wikipedia.org_1
wikipedia.org_2
earthquake.usgs.gov
sciencing.com
geo.mtu.edu
greekmythology.com
Thank you for stopping by and giving this post a read. I hope you enjoyed it! If you please, feel free to pay a visit to my blog and check out my short stories along with plenty of educational posts and of course my bizarre natural phenomena series.
Until my next post,
Steem on and keep smiling, people!
