Friday, May 6, 2016

How was a(n) Earthquake Created?



Analog models are common ways not just to understand how something works, but to study how something works. A Lava Lamp is an analogue for how volcanoes evolved from lighter magma moving up through weakened structures in the earth’s crust. Of course it’s not as simple as that, because there are scaling laws for the different physical properties that are involved. A scale model used to study how sand moves under the influence of waves cannot use the same size of sand as what you are interested in modeling. Physical processes such as surfactants, surface tension, charge-transfer, and grain-edge interactions among other things will all be different.

Q: how was a earthquake created
- Markez G

A: Here's an analogue way to get a physical understanding of how an earthquake happens:

Take an unpolished slab of wood - it could be a piece of un-sanded plywood or a raw two-by-four. Find a block of some other un-sanded wood and place it on the first piece. Push down hard, pressing and holding the two together. This would be the equivalent of lithostatic pressure in the Earth that keeps faults from slipping and sliding constantly.

NOW begin putting side-ways pressure or force on the upper block or piece of wood - but still maintain the vertical pressure (the lithostatic pressure) that is keeping the two pieces of wood together. As you increase the sideways force (this increasing sideways force would be the equivalent of the strain buildup that leads to an earthquake) the upper piece will eventually, suddenly, slip. This is the equivalent of an earthquake. The plane where they slip with respect to each other is the equivalent of an active fault. Fault planes in the real Earth can be vertical or horizontal or any angle in between. The San Andreas fault in southern California is mostly a vertical fault plane (or collection thereof), while the Northridge (Los Angeles) earthquake of 1994 was caused by movement along a buried horizontal plane not visible at the surface.

Did you notice the squeaking or shrieking sound that happened when the two pieces of wood suddenly started to move with respect to each other? That is the equivalent of the seismic waves released by an earthquake. In the real Earth world this sound is much lower in frequency, usually something more felt than heard. The farther away you are, the fainter the sound, because like earthquake waves the energy is attenuated (both absorbed and dispersed) with distance.

I hope this analog of an earthquake makes it easier to comprehend.

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