Earthquakes

[LR89]

I'm learning about earthquakes in one of my classes and am unsure about what type of interactions at plate boundaries can cause them. Can earthquakes occur at a continental-continental convergent plate boundary? Or is mountain formation the only result when the continental plates collide?

[Horza2002]

Your right so far in that earthquakes only occur at fault lines (i.e. where plates meet). If I remeber rightly, earthquakes are not caused by collisions of the plates. Earthquakes occur when plates are moving past each other (parallel sort of) in opposite directions. The friction can stop them from moving and they get stuck. This carries on until one plate suddenly slides past the other which is then the earthquake.

 

Plates colliding (i.e. moving towards each other) is what creates mountains. One plate is forced up and over the other causing it to move upwards.

 

Plates moving away from each other is where you tend to get volcanoes because there is a gap that allows magma to reach the surface.

[zapatos]

Your right so far in that earthquakes only occur at fault lines (i.e. where plates meet).

Earthquakes can also occur far from the edges of plates, along faults. Faults are cracks in the earth where sections of a plate (or two plates) are moving in different directions. Faults are caused by all that bumping and sliding the plates do. They are more common near the edges of the plates.

 

http://www.geo.mtu.edu/UPSeis/where.html

[Horza2002]

Sorry yes I meant to say that they are more common at fault lines since we do get earthquakes here in GB.

[Ophiolite]

Sorry yes I meant to say that they are more common at fault lines since we do get earthquakes here in GB.

I cannot envisage how you could get an earthquake without a fault line. ....... No, I tried again and it just doesn't work. Certainly the British quakes all occur along fault lines.

[Horza2002]

Unless I'm mistaken, the UK s not on any fault lines, its in the middle of a plate. So I guess the tremors must be passed through the plate until it gets here.

[insane_alien]

actually, there are a number of fault lines in the UK.

 

there is a difference between a fault line ang a tectonic plate boundary.

[zapatos]

I believe you can also get earthquakes from volcanos, and volcanos are sometimes not at the edge of plates. (although I don't think the UK has many active volcanos!)

[Horza2002]

Insane Alien, whats the difference? I was always taugh in geography that fault lines and tectonic plate boundaries are the same thing.

[zapatos]

"Earthquakes can also occur far from the edges of plates, along faults. Faults are cracks in the earth where sections of a plate (or two plates) are moving in different directions. Faults are caused by all that bumping and sliding the plates do. They are more common near the edges of the plates."

 

http://www.geo.mtu.e...Seis/where.html

 

Some of the bigger earthquakes in the US were near the center of the country far from the edges of plates.

 

" ...after December 16, 1811, there could be no doubt about the area's potential to generate severe earthquakes. On that date, shortly after 2 AM, the first tremor of the most violent series of earthquakes in the United States history struck southeast Missouri. In the small town of New Madrid, about 290 kilometers south of St. Louis, residents were aroused from their sleep by the rocking of their cabins, the cracking of timbers, the clatter of breaking dishes and tumbling furniture, the rattling of falling chimneys, and the crashing of falling trees. A terrifying roaring noise was created as the earthquake waves swept across the ground. Large fissures suddenly opened and swallowed large quantities of river and marsh water. As the fissures closed again, great volumes of mud and sand were ejected along with the water.

 

The earthquake generated great waves on the Mississippi River that overwhelmed many boats and washed others high upon the shore. The waves broke off thousands of trees and carried them into the river. High river banks caved in, sand bars gave way, and entire islands disappeared. The violence of the earthquake was manifested by great topographic changes that affected an area of 78,000 to 130,000 square kilometers.

 

On January 23, 1812, a second major shock, seemingly more violent than the first, occurred. A third great earthquake, perhaps the most severe of the series, struck on February 7, 1812."

 

http://earthquake.usgs.gov/earthquakes/states/missouri/history.php

Edited October 6, 2010 by zapatos

[dragonstar57]

I'm learning about earthquakes in one of my classes and am unsure about what type of interactions at plate boundaries can cause them. Can earthquakes occur at a continental-continental convergent plate boundary? Or is mountain formation the only result when the continental plates collide?

no incorrect earth quakes can happen at converging boundaries

ever heard of a Subduction zone?

[Awang ASDU]

I think it's better to start from mechanical approach especially about deformation. There are two kind of deformation those are: brittle (accomodate by translation and rotation) and ductile (accomodate by dilatation/change in volume and distortion/change in shape. In this case concern may take in brittle deformation. Brittle means material acted by strees follow elastic (be able to back to original condition if yield strength do not achieve) mechanism until yield strength achieved and then failure so deformation will occurs if given force exceed material strength . When material failure, it's released energy as a shock. This kind of shock in rock mass I think that what people call earthquake.

 

So no matter where or when if this mechanism as explain above occurs, earthquake will happen. In geology point of view it’s occurs in : magma chamber, when magma penetrate rock wall (vulcanic earthquake), plate convergen such us subduction, collision, obduction (tectonic earthquakes) even in passive margin (unactive plate boundaries), deep water avalance (potential energy release). Energy released by forming of fracture, fault, fault/fracture propagation, elastic rebound mecanism etc.

 

 

[HerpetologyFangirl]

Plate boundaries where the two plates slide past each other in opposite directions are called 'Transverse Plate Boundaries'. A good example of such a boundary is the San Andreas fault in California, America. Faults and Plate Boundaries are not the same thing. Plate Boundaries are the lines dividing up and seperating the plates, the plates' edges. Faults are any area with unstable geology, they can occur in the middle of plates, or just about anywhere, not just on the edges of plates, although that's where they're most common.

Edited November 22, 2010 by HerpetologyFangirl

[marshall02]

There are Earthquakes on almost a daily basis. You have not stated where in the world you live, so therefore i cannot let you know if there was or not, but you can find out by following the link below.

 

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Vivarium tanks

[JohnB]

Just to add. Earthquakes and faults can be caused by vertical pressure as well as horizontal.

 

During the last Ice Age the areas beneath the ice shields were depressed, Scandinavia was depressed some 800 metres. Once the ice receeded and the weight was gone, faults and their accompanying earthquakes occurred. The full name is "Post Glacial Isostatic Rebound". This is also the reason for faults in England. Southern England was raised by the pressure of the ice to the North while Scotland was depressed. Scotland is still rising from the rebound while Southern England is slowly sinking.

[IronParrot]

An earthquake is a phenomenon that results from and is powered by the sudden release of stored energy that radiates seismic waves. At the Earth's surface, earthquakes may manifest themselves by a shaking or displacement of the ground and sometimes tsunamis, which may lead to loss of life and destruction of property.

 

Earthquakes may occur naturally or as a result of human activities. In its most generic sense, the word earthquake is used to describe any seismic event—whether a natural phenomenon or an event caused by humans—that generates seismic waves.

 

Most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes. The Earth's lithosphere is a patch work of plates in slow but constant motion caused by the heat in the Earth's mantle and core. Plate boundaries glide past each other, creating frictional stress. When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure occurs is called the fault plane. When the failure at the fault plane results in a violent displacement of the Earth's crust, the elastic strain energy is released and elastic waves are radiated, thus causing an earthquake.

 

You could get more information from the link below...

http://en.wikipedia.org/wiki/Earthquake

[OSHMUNNIES]

Just to summarize (and possibly simplify) the definition of an earthquake here...tremors can be caused by any substantial release of energy; the interaction of two plates, the formation (or propagation) of a fault (which may or may not be part of a plate boundary), and any pressure-driven volcanic or magmatic anomaly can all release the amount of force and energy necessary to cause the phenomenon we call an "earthquake."