Why do earthquakes occur far away from plate boundries?

04 October 2011

Haiti_Earthquake_building_damage.jpg

A man exits a restaurant after he looked for his belongings. An earthquake rocked Port au Prince on January 12, 2010.

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Question

I was on a business trip recently and experienced the earthquake, the 5.8 in Washington DC. My question is why do quakes occur that are nowhere near a tectonic plate boundary?

Answer

Dave Ansell considered this question...

Dave - Yes, Washington DC is nowhere near a plate boundary. There's a variety of things and, basically, anything which can apply large forces to the plates can cause earthquakes. You can also get earthquakes a long way away from plate boundaries, actually still associated with them.

So, in India, where you're creating the Himalayas and you've got a huge amount of compression, you can still get earthquakes hundreds of miles away from that plate boundary, just because the compression and the crushing there is so immense.

You can also get earthquakes when people build big reservoirs: so you put a load of water on the ground. That essentially loads it, so the comfortable place where the ground wants to be is a bit lower, so the only way it can move there - if it's not squidgy like clay - is by cracking, and so you get small earthquakes like that.

You can get earthquakes as ice melts - we're still getting earthquakes in Norway and actually, most of the earthquakes in Britain are probably associated with all the ice melting after the last ice age. In the north end of Britain, and in Norway, the ground is rising slowly actually a few centimetres a year, especially in Norway, and that eventually builds up some pressures and stresses in some places until it breaks.

I think the one thing I vaguely heard about the Washington earthquake is that it could also be sediment building up off the edge of the continent, building up on the ground that's pushing down and, eventually, that could build up enough to create an earthquake...

Comments

i think studying earthquakes is cool but what are the earthquakes called that are far from plate boundaries and why do they occar??

What are the earth quakes called that are far awqy from the plate boundaries, and how do they ocur ?

Thank you so much this helped a lot with my project

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