Earthquakes are a bizare phenomenon that can be explained but predicting when they occur is still a puzzling concept. The Earth is made up of differents layers. The layer which humans and earth processes have modified is the thin outer crust made up of rock materials. This crust is put together like a puzzle and the pieces are called plate tectonics. These plates are always and have always been continuously moving.
When these puzzle pieces converge, diverge and slide past one another we experience the dreaded earthquake.
Underneath the crust is the mantle this is the second layer of Earth. The mantle has different layers to it but the one closest to the lithosphere, or crust, is the Asthenosphere a bendable molten mixture that the tectonic plates float on. The Asthenosphere is the driving force of the movement of the plates. Where these puzzle pieces meet are ridges that have new molten material that pushes up through the crust through convection and spreads out, called sea floor spreadin. When new material is added to the crust pressure builds along the edges of these puzzles pieces(tectonic plates) until the pressure is too much to take and energy is released in the form of an earthquake.
One of the well known, earthquake prone areas of the United States is the San Andres Fault located in California. Fault lines are associated with plate boundaries. In the case of the San Andres Fault we see a Transfom boundary of the Pacific and North American plates. There are several types of boundries between plates with different characteristics and movement. Transform Boundries are charaterized by their
horizontal movement past one another and lateral displacement of Earth’s crust. The two plates slip past one another when the pressure is too intense for the Earth’s crust and therefore the Earth under our feet shifts in a violent movement and jolt.
Areal view of the San Andreas Fault
Earthquakes origin of movement is relatively shallow. The pressure is released at the focus point, and or the center of the fault’s motion. This focus sends shock waves further below the origin and above. The area directly above the focus on the Earth’s crust is the epicenter. It is here that the wave of released energy in the earths surface is felt.
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