Earthquakes- Reason for the ground to shake

Earthquakes- Reason for the ground to shake

Question:-Earthquakes occur around the globe and are higher in the regions where convergence of plates takes place. Examine the reasons for occurrence of earthquakes.

- The earth is made up of four layers amongst which the crust and the mantle make a thin layer on the surface, which in turn is made up of many pieces. These pieces move around slowly, sliding and bumping against each other. These pieces are the tectonic plates and the edges of these are called plate boundaries. The continental and oceanic plates are constantly moving against each other, sliding or pulling apart

- The plate boundaries consist of numerous faults and this is where an earthquake occurs. The ramming of two plates against each other causes the the boundaries to get stuck since they are rough, while the rest of the plate keeps moving. Finally the edges break on one of faults causing the ground to shake in form of an earthquake.

- During and post an earthquake the plates continue moving until they emerge together again. The point where the rock breaks underground is the focus of the earthquake and the point above the focus on the ground is the epicenter.

- Most earthquakes arise along fault zones where the ground first bends and then snaps to release energy along faults.

Ways in which an earthquake may occur

Strike-Slip: A sideway movement of the crust results in a horizontal motion along a strike slip fault. San Andreas Fault in California is the best known example. The branches of the fault moving sideways is caused by the Pacific ocean's crustal plate moving toward northwest under North America's continental crust.

Dip Slip: The vertical movements in earthquakes occur over dip-slip faults where the fault zone either drops or is pushed. A drop occurs where the deeper part of crust is being pulled away from an overlying part. The Wasatch fault is an example of this type.

Oblique: These are the kinds where faults are combined sideways with the vertical movements. The Santa Clara Valley has a fault susceptible to oblique movements.

Facts:

- Each year the southern California area has about 10,000 earthquakes -- the majority of which go unnoticed. However, if there is a large earthquake the aftershock sequence will produce many more earthquakes of all magnitudes for months.

- The earth's surface consists of 20 constantly moving plates.

- The largest recorded earthquake in the US was a magnitude of 9.2 that struck Alaska on March 28, 1964 and the largest recorded earthquake in the world recorded 9.5 on the Richter scale in Chile on May 22, 1960.