A Beginner’s Guide to Earthquakes
By Brendan Mitchell
The Crumbling of a Nation
The 1960 earthquake in Chile killed 1,655 and left an astounding 2,000,000 homeless. While we might never prevent such tragedies, understanding the science behind earthquakes is a dire step towards lowering casualties and damages. Many already know earthquakes usually result from the movement of tectonic plates, which are part of the Earth’s crust.
The Shifting Earth
Many don’t know how and why tectonic plates move. To understand this, we need to understand Earth’s structure. The inner core of Earth is a compressed and intensely hot culmination of nickel and iron. Despite the inner core being solid from compression, the outer core is considered a viscous flowing liquid also made of nickel and iron.
https://worldstogether.wikispaces.com/The+Restless+Earth
The mantle is the largest portion of Earth in terms of area, and it contains solid magma (flowing heated rock within Earth). Magma is is also vital to the formation of volcanoes and earthquakes, as explained in this article. Finally, the crust is the outer layer of Earth, which includes tectonic plates: massive chunks of solid rock and mineral. These plates slowly shift, and their interactions cause most earthquakes. Tectonic plates vary wildly in area, as shown in the chart below.
The World’s Lithospheric Plates
http://geology.about.com/library/bl/blplate_size_table.htm
| Plate | Area (km2) | Plate | Area (km2) |
| Pacific | 103,300,000 | Scotia | 1,600,000 |
| North America | 75,900,000 | Burma microplate | 1,100,000 |
| Eurasia | 67,800,000 | Fiji microplates | 1,100,000 |
| Africa | 61,300,000 | Tonga microplate | 960,000 |
| Antarctica | 60,900,000 | Mariana microplate | 360,000 |
| Australia | 47,000,000 | Bismark microplate | 300,000 |
| South America | 43,600,000 | Juan de Fuca | 250,000 |
| Somalia | 16,700,000 | Solomon microplate | 250,000 |
| Nazca | 15,600,000 | South Sandwich microplate | 170,000 |
| India | 11,900,000 | Easter microplate | 130,000 |
| Philippine Sea | 5,500,000 | Juan Fernandez microplate | 96,000 |
| Arabia | 5,000,000 | Rivera microplate | 73,000 |
| Caribbean | 3,300,000 | Gorda microplate | 70,000 |
| Cocos | 2,900,000 | Explorer microplate | 18,000 |
| Caroline microplate | 1,700,000 | Galapagos microplate | 12,000 |
Tectonic Plate Earthquakes: The Basics
Because these gargantuan plates are free to slide across the Earth’s surface, collisions are inevitable. Any two adjacent plates are capable of pulling apart from each other, grinding past each other, or smashing together.
http://www.worldatlas.com/aatlas/infopage/tectonic.htm
An interaction between plates is called a boundary, and there are three types. The first is a convergent boundary. This is when plates are moving towards each other and one submerges itself underneath the other. Such contact stores up energy in the submerged plate, which can often cause earthquakes when it snaps back into place. Transform boundaries happen when two plates grind past each other, sometimes forming a fault where earthquakes can also occur. The final kind of boundary is a divergent boundary, where plates move apart and there is no potential for an earthquake.
At a convergent boundary earthquake the submerged plate snaps back into place and the released energy causes tremors. Transform boundaries create faults, or cracks in the crust. This page illustrates how earthquakes occur at a transform boundary.
Volcanic Earthquakes
So, earthquakes are always caused by tectonic plates?… Right? Actually, no. Earthquakes can be provoked in many ways: due to underground explosions, the collapse of man made structures, and volcanoes. In fact, natural earthquakes can be categorized into two categories: quakes caused by lithospheric plates, and those caused by volcanoes.
As psn.org explains, volcanic earthquakes are caused by the flow and irritation of magma in a volcano. When enough energy builds up in a volcano, magma can damage surrounding rocks and send vibrations throughout the surrounding area. Such earthquakes generally are of much less magnitude and cause less destruction than tectonic plate earthquakes, but they can foreshadow volcanic eruptions.
Shudders of the Earth
While there are different kinds of earthquakes, they all have important similarities. Every earthquake has a focus, which is the underground position marking the earthquake’s center. From here, the energy from the quake is dispersed evenly in all directions in the form of longitudinal waves. The point on Earth’s surface directly above the focus is the epicenter, which is where the most damage is generally caused. Earthquakes have less energy farther from the epicenter because waves spread out more and more from it due to the three-dimensional travel pattern of seismic waves.
http://www.instructables.com/id/The-Steps-to-Locating-the-Epicenter-of-an-Earthqua/
The primary way of measuring earthquake magnitude at is by using a seismograph. This instrument measures the amplitude of seismic waves at its location, relaying the energy of the quake at that point. The magnitude of earthquakes is measured by the Richter Scale, which is a logarithmic scale ranging from 1-10 (10 is the highest magnitude). Because the scale is logarithmic, the difference between an 7.0 and a 8.0 quake is much greater than the difference between a 4.0 and a 5.0.
http://kids.britannica.com/elementary/art-183759/Scientists-record-the-shock-waves-produced-in-an-earthquake-with
Earthquakes causing mass destruction are generally above 8.0, although the 1960 Chile earthquake was a 9.5 at its epicenter. Even though earthquakes of such intense magnitude will inevitably cause devastation, scientists’ understanding of earthquakes has led to many positive breakthroughs. From the advances of shock-resistant buildings to the study of seismology, our constantly growing knowledge of earthquakes is and will continue saving lives for generations to come.
Citations:
http://www.bbc.co.uk/schools/gcsebitesize/science/21c/earth_universe/changing_earthrev5.shtml
http://www.britannica.com/event/Chile-earthquake-of-1960
http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php
Just a Random blog 
When I think of an earthquake, I think of one caused by tectonic plates because you always hear in the news about the big earthquakes caused by plates shifting. I really never knew that volcanoes could cause earthquakes. I also did not know about the different kinds of boundaries between plates. I knew about the convergent boundary, but the divergent and transform boundaries are new to me. I recently read something about preventing huge earthquakes that normally kill a lot of people. The scientists figured out that there are small vibrations that occur before big earthquakes. So, they when their seismographs sensed small vibrations, they would send out an alert for people to evacuate buildings. I forget what country this was in, but I thought that it was cool and it did end up saving a lot of lives. Overall, good job on your blog post, and it looks very nice.
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Thanks for your interest and your complements Drew! I think the kinds of boundaries are interesting too, especially because they cause so much: earthquakes, volcanoes, mountain ranges, and deep sea trenches. I’ve also learned about the foreshocks that come before earthquakes. I learned in Earth Science last year that they are basically slight tremors caused by the minor shifting of plates before they move a great distance and cause huge earthquakes. It’s awesome that scientists are learning more and more about earthquakes, because as you said when they can be somewhat predicted many lives can be saved.
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