Whats the relationship between plate boundaries, earthquakes and volcanoes.?

Question

Can volcanoes and earthquakes occur at locations other than plate boundaries?

Answer 1

Earthquakes:
It all comes down to stress and strain from the interaction of different plates, chiefly at the boundaries. 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, they 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.

It is only in rare cases when this stress is transfered to the interior of a plate. This is a much slower and more subtle process that is pooorly understood. The most famous one is the New Madrid fault zone, near St. Loius.

Volcanoes:
There are several processes in Plate Tectonics that cause volcanism, but they result in two main types of volcanism.

Volcanism in subduction is caused by volitals, like H2O, CO2. These are carried down by the plate, mainly in the form of weak minerals. These minerals break down with pressure and temperature into stronger minerals that don't contain water and carbon dioxide. The leftover gases and liquids travel into the mantle (the mantle wedge) and hydrate the mantle, causing melting. The melt rises and then... volcano!

The other main cause is from rising mantle material, which forms decompression melting. Basically, hot mantle is kept from melting by the pressure of the earth at depth. When this material rises, the pressure drops much faster than the temperature, and thus it partially melts. This mainly occurs at divergent boundaries and hot spots, which are areas in plate tectonics that have rising materials or spreading.

Answer 2

Yes, volcanoes and earthquakes occur at locations other than plate boundaries. For example: Kilauea and Mauna Loa volcanoes on the island of Hawaii are pretty much in the middle of the Pacific plate and there are about 4000 earthquakes a year in Hawaii (most are very small and not felt by people).

Answer 3

Major earthquakes are bound to happen only in plate boundaries. volcano depends upon some other condition.Minor earthquakes may happen at any place other than major fault lines. There are about 7 major fault lines and about 13 small fault lines we have found. But there is no place in earth free from earthquakes. The places which will be affected by volcanoes are well known. Please visit my slide show
My Community in Orkut
http://www.orkut.com/Community.aspx?cmm=26068261
Presentation slides
http://asia.pg.photos.yahoo.com/ph/quake

Answer 4

volcannoes can etupt at very thin parts of a Plate, these can cause earthquakes. So earthquakes and volcanoes can form at different locations.

Answer 5

I believe there are lots of different ways there can be stresses in the earths crust.... so yes, I believe it is possible to have a volcano or earthquake, not directly linked to plate edges rubbing noses... ;)