why do we have earthquakes?

Answer 1

It all comes down to stress and strain. It is not 'the plates rubbing together' as many people say; or at least that's a very simplistic view.

Plate tectonics causes stress on the continents and oceans, all over the surface of the earth. In some places, the stress is very small (usually within the plates). Elsewhere, the stress is high, usually where the plates meet each other. Since each plate moves, when two come in contact, the stress each other. They can push on each other and cause compressional stress, they can pull with extensional stress, and they can slide past or shear each other with tensional stress.

Faulting, causing earthquakes, comes from the fact that this stress is building up all the time, but rocks and continents are strong materials. Just like hitting a rock with a small hammer, you do put stress on it, but a small amount. It would take a sledgehammer to put enough strain (effects and accumulation of stress) to build up and cause breakage. In the earth, the area around an active fault builds up strain from the stress of plate tectonics. Most faults become locked, because of this strength, and thus can not release their strain. Away from the fault, the stress produces very small and slow movement of the rock masses as a whole. Eventually, the strain is too much and the rest of the plate has moved too far and the fault releases the strain build-up all at once in a big stress release called an earthquake. This is called the elastic rebound theory, and it explains most (but not all) movements.

This is why an earthquake's size is relative to the fault size. The bigger the fault, the bigger the strain build up, and the bigger the release in an earthquake. Subduction zones and collision zones, where large portions of plates actually can rub together as a whole, have the really big earthquakes, like the 2004 Sumatra earthquake. In other plate boundaries, the entire plate boundary does not act together, so the faults become spread out and many faults take up the strain from the tectonic stress, like with the San Andreas Fault in California (it only takes up ~3/4 of the stress between the plates).

Earthquakes are really tricky things; there is still so much we need to learn. As of now, there is no way to predict them, but we can say where the danger is highest and about how long between events.

Answer 2

Earth scientists believe that most earthquakes are caused by slow movements inside the Earth that push against the Earth's brittle, relatively thin outer layer, causing the rocks to break suddenly. This outer layer is fragmented into a number of pieces, called plates. Most earthquakes occur at the boundaries of these plates.

Answer 3

I think it's the frequency with which they are happening, along with the death-toll, that is worrying. Haiti on January 14 (scale - 7); Chile on 27 February (scale - 6.2); Turkey on 8 March (scale 6.2) and Sumatra on 6 April (scale 7.8). Regardless of whether this is perceived as nothing abnormal, the effect on human lives has been devastating. It will only take an earthquake in a densely populated area such as the U.S.A. for some people to wake up. One of the many signs of the end of the age is "great earthquakes, famines and pestilences in various places, and fearful events and great signs from heaven" (Luke 21:11). Needless to say, there have been great earthquakes, famines and pestilences for the last 2,000 years. What demands our attention, from God's point of view, is that despite all the trials and tribulations that will culminate in the end of the age, those who have placed their faith in Christ Jesus as Lord and Saviour, and who stand firm, need not fear. "There will be signs in the sun, moon and stars. On the earth, nations will be in anguish and perplexity at the roaring and tossing of the sea. Men will faint from terror, apprehensive of what is coming on the world, for the heavenly bodies will be shaken. At that time they will see the Son of Man (Jesus Christ) coming in a cloud with power and great glory. When these things begin to take place, stand up and lift up your heads, because your redemption is drawing near" (Luke 21:25-28). I suspect things are going to get an awful lot worse before they start to get better.

Answer 4

Plate tectonics i.e. the movement of the crust, which is divided up into distinct sections called plates can collide causing earthquakes.

Answer 5

The earth is still forming, so the tectonic plates are still shifting very slowly... when the move, this causes breaks in the ground - earthquakes.

Answer 6

We have earthquakes because the plates are moving and when they move they might run into another plate and causes the plates to grind together.

Answer 7

This Site Might Help You.

RE:
why do we have earthquakes?

Answer 8

im sure you know that the planet is formed of giant plates floating on an ocean of molten rock.
when the plates move you get an earthquake

Answer 9

Shaking and vibration at the surface of the earth resulting from underground movement along a fault plane of from volcanic activity.

Answer 10

Plates scrape byeach other, sending shockwaves on both sides.