Earthquake 101 – Some Things You Need To Know

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Image: Earthquake Unit, UWI Mona

Hello diGgers,

How much do you know about earthquakes – what causes them, the technical terms associated with them, how they are measured, and so on? Since we are currently in Earthquake Awareness Month, diGJamaica has put together a fact sheet to help you understand more about these dangerous, destructive natural phenomena. Take a look!

What is an earthquake?

According to the United States Geological Survey (USGS), “An earthquake is what happens when two blocks of the earth suddenly slip past one another.” These “blocks” are tectonic plates – sections of the earth’s mantle and crust – that are always in slow but constant motion. The edges of these plates are called plate boundaries, which are made up of many faults. Most earthquakes occur along these faults. Since the edges of the plates are rough, they get locked together. Energy that would normally cause the blocks to slide past one another accumulates between them, while the rest of the plate keeps moving. Finally, when the plates have moved far enough, the edges unstick on one of the faults and there is an earthquake as this built-up energy is suddenly released and travels through the earth in the form of seismic waves.

Plates move in three ways:

stress_types
Image from USGS, via Michael Kimberly – North Carolina State University
  1. Away from each other at divergent or constructive boundaries. This type of movement causes mid-ocean ridges or rift valleys.
  2. Towards each other at convergent boundaries (also called compressional or destructive boundaries), where one plate is forced underneath the other in a process called subduction. Earthquakes and composite volcanoes are common at this type of boundary.
  3. Past each other at transform boundaries. The most famous example of this boundary is the San Andreas Fault, located in California, USA. (BBC Science)