do mountains affect earthquakes in any way?

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- kephas
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do mountains affect earthquakes in any way?
OP - December 26, 2014, 12:10 PM

Do mountains affect earthquakes in any way? I mean, even if the effect is small? maybe their mass causes the earth under them more difficult to move, or that they create friction, etc?

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do mountains affect earthquakes in any way?
Reply #1 - December 26, 2014, 02:05 PM

Well as far as I understood as a layperson, not a geologist, the cause and effect was the other way around, ie mountains forming from the pushing together of tectonic plates leading to seismic activities.

Any geologists here?

Edit: Seems like I have the general idea more or less right, although there's a lot more depth depending on the type of mountain you're making. http://en.wikipedia.org/wiki/Mountain_formation

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- kephas
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do mountains affect earthquakes in any way?
Reply #2 - December 26, 2014, 02:59 PM

yea but I wondered if what happens after the earthquake when mountains are formed. like let's say if there's this region where there are no mountains in the beginning. then an earthquake happened. thus a mountain is formed. somehow the existence of the mountain causes the amplitude of any future earthquake to reduce, etc.

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do mountains affect earthquakes in any way?
Reply #3 - December 26, 2014, 05:50 PM

Topography creates an effect known as intensity compression. An earthquake is ground motion so think it is as a series of wave within materials that are usually more dense than water. Some materials are more dense by nature or are compressed mixtures. For example sandstone is a mixture of sand, quartz, clay, etc which is more dense than sand covering a desert. Density of a material effects how the wave is dissipated within the material and to the material surrounding it. Mountains are more dense so the compression amplifies a quakes effects on the mountain and in proximity to the mountain which is between it and the source of the quake. If the mountain is between you and the quake source there is a reduction in the motion of the wave other material. So the effect a mountain has on a quake is situational only. However this is no solely linked to mountains alone. Density of material under our feet can also be applied to this.

I am not sure how to explain it without getting deeper into physics.
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do mountains affect earthquakes in any way?
Reply #4 - December 26, 2014, 06:19 PM

Topography does seem to influence how seismic waves seem to propagate. From what I recall, valleys tend to have reduced ground motion.

However, I do not know to what extent mountains tend to have on the magnitudes of earthquakes. Has it been ever quantified?
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Reply #5 - December 26, 2014, 10:51 PM

Mountains are classified under surface irregularities which have an effect on wave motion. However such irregularities amplifies the wave rather than reducing it. There is no true reduction of the magnitude of the quake just variation of the amplification objects create due to resonance.
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do mountains affect earthquakes in any way?
Reply #6 - December 27, 2014, 07:57 AM

Quote from: kephas on December 26, 2014, 02:59 PM
somehow the existence of the mountain causes the amplitude of any future earthquake to reduce, etc.

I don't believe it affects the amplitude, but it might impact the frequency. When there was a 5.8 earthquake in Virginia in 2011 (the biggest in over 100 years), it was felt from Florida to Ontario, because the east coast's rock formations are extremely old and have sort of cemented together with time (because of erosion and other processes), meaning that when one moves, they all move. The mountain chain there, the Appalachian mountains, is believed by many scientists to be the oldest in the world, and used to be taller than the Himalayas. Whereas in California, there are earthquakes all the time, and they are barely felt outside the city they happened in. This is because that area and its mountains (the Rockies) are very young geologically speaking, and aren't cemented together, so when an earthquake happens it doesn't travel as far.

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