Groundbreaking Earthquakes

If you have been following up on the news recently, there have been a few earthquakes in Chile and the US. To a layman, all earthquakes may look similar, save for the difference in intensity and magnitude. But as we all know, that is simply not true.

We first need to understand what earthquakes are before we can differentiate them. Earthquakes are essentially are the result of the release of the stress accumulated between rocks on the surface of the Earth. The surface of the earth is split into different plates, each with its own direction of movement. At the border of these plates, known as a fault line, friction will accumulate as they move against each other. Over time, as the amount of stress and friction accumulated exceeds the tensile strength of the rocks, the fault slips and releases the stress. This triggers the ground movement that we know as earthquakes.

One key difference between the faults is the direction of movement of these plates. Faults can be roughly classified into transform, reverse and normal faults. Transform faults are where plates are parallel to each other but they move in opposite directions as seen on the right.

From the diagram, the North American Plate is moving in a south-easterly direction whereas the Pacific Plate is moving in a north-westerly direction. The friction generate from this motion will thus trigger earthquakes such as those seen around Los Angeles earlier this week. The fault system on which Los Angeles and San Francisco lie on is known as the San Andreas fault.

On the other hand, the earthquake seen in Chile is a reverse fault. A reverse fault, as in the case of Chile, occurs when two plates converges and moves towards each other. From the diagram below, we can see that a continental plate and an oceanic plate are moving in opposite directions. In the case of Chile, they are the South American and Pacific plates respectively. As the oceanic Pacific plate is denser than the continental South American plate, it subducts beneath the continental plate. This movement generates a significant amount of stress along the fault line where these two plates meet. Once again, when the accumulation of stress exceeds the tensile stress of rocks on both plates, an earthquake occurs.

Of course, this is just a simple overview that seeks to shed light on the difference between the two earthquakes that has rattled us recently. If you wish to know more or have any other questions, please feel free to contact us or leave a comment below.