1) Plate Tectonics

This part of the blog may seem boring or irrelevant but for those who are genuinely interested into what causes these earthquakes, I strongly encourage you to read on. For those just wanting to know about the hazards, that is further up the blog.

Although it may seem obvious, it is good to sometimes ask ‘what is an earthquake?’. To understand this, we must first understand plate tectonics. As I am sure most of you are familiar with, plate tectonics describes the process of movement of solid sections of the earth’s surface. These plates all interact with each other, much like different cheeses on top of hot pizza or ice cubes in a glass of water.

Sometimes one plate can sink beneath another one. This is called a subduction zone, where one, denser (heavier per m³) plate gradually sinks beneath another. The most relevant example of this is when an oceanic crust is subducted (sinks beneath) a continental crust. This is called a cnvergent plate boundary, as the plates move into each other In this situation, as the oceanic plate sinks it forms an ocean trench. These trenches can be many kilometres deep. This is relevant to Ecuador as just 100km off the coast there is a convergent plate boundary and a trench. The two plates interacting here are the Pacific plate (the ocean bit) and the Nazca plate (the land bit). These zones are usually associated with seismic activity, which is why this blog exists.

Now with the boring (albeit necessary) background out of the way, we can answer the first question: What is an earthquake?

An earthquake an be compared to a coiled spring, both have the common point of stress. When the spring is released a huge amount of energy is passed through it. We can use this analogy in close relation to Ecuador, an earthquake in Ecuador is created when the stress is built up through friction; as the subducted plate passes the other plate it builds up stress until it is suddenly released.There are other causes of stress in the crust, however it is this process that creates the largest earthquakes.

The diagram will hopefully better explain the idea of a subduction zone. The lithosphere means the surface of the earth that is solid, the asthenosphere means the part that has melted.

(Sourced from http://study.com/academy/lesson/subduction-zone-definition-location-example.html)

However, unfortunately for Ecuador this is not the only plate movements and interactions. In the northern parts of the Andes, there is a smaller plate that is not as obvious as the Nazca or South American plates. It is called the North Andean Plate. This plate has a boundary (the edge of a plate, where plate interactions occur) with the Nazca plate that runs through the high valleys in the Andean parts of Ecuador around Quito and Riobamba. This is what forms the large mid-Andean valley where these two cities are. This boundary has created numerous and complex faults. A fault is a part of the earth's surface that has cracked into two or more obvious sides due to earth movements. These faults run down the spine of the Andean regions of Ecuador and finish in the Gulf of Guayaquil. The nature of this plate boundary and these faults is still under research and quite complex, so I will not cover them in much detail.