I basically want to understand if earthquakes can simply happen anywhere, or if there are some conditions for earthquakes to happen in an area.
In: Planetary Science
Yes, they can happen anywhere on Earth, since an Earthquake is basically just a shaking of the Earth’s crust that is created by seismic waves. But they occur most often where two tectonic plates in the Earth’s crust meet.
They happen due to slip on a [fault plane.](https://en.wikipedia.org/wiki/Fault_(geology)) There are faults throughout the tectonic plates but they are concentrated at or near plate boundaries. Intraplate earthquakes can occur very far from plate boundaries, (usually as a result of built up stress reactivating an old fault that exists from when that area used to be associated with a plate boundary in the geologic past), though they are definitely not as common or as large in magnitude.
All of the above is thinking of earthquakes due to tectonic forces, ie. due to stress building up because tectonic plates move around, but there are also earthquakes that can occur due to magma moving through the crust. Magma can (and does) fracture it’s own paths through the Earth’s crust, this sort of thing is monitored in volcanically active regions to help give an indication of when eruptions might be imminent. The sorts of earthquakes that get generated by magma movement are distinguishable from the purely tectonic ones, they tend to occur as a bunch of similar magnitude events close together known as earthquake swarms.
People will probably tell you that Earthquakes are due to fault lines, subduction zones, volcanic stuff and such things. That’s _mostly_ correct, the strongest and most common earthquakes are usually of that nature.
But there are other sources. The collapse of underground caverns or similar cave-ins can cause immense shaking. This for example is one of two hypotheses how the one that [flattened the Swiss city of Basel in 1356](https://en.wikipedia.org/wiki/1356_Basel_earthquake) happened. Other underground events such as nuclear tests also shake the earth, but our typical bombs are too weak (yes, nukes are puny compared to many quakes) to cause more than some rumbling.
The impact of a large asteroid also causes intense earthquakes, but this might only by number 7 or so on your list of immediate problems.
Because “earthquake” only means “the ground starts shaking,” they can happen anywhere–but the reasons will differ from place to place. A cave collapsing, for example, can cause an earthquake.
*Most* earthquakes are caused by plate tectonics (read: the Earth’s crust is not one solid sphere, it’s a bunch of chunky bits sitting on top of the mantle, and sometimes they push against each other or under/over each other), but some are caused by volcanism, very large impact events (e.g. the asteroid that killed the dinosaurs), or other such things.
As a general rule, though, *major* or *frequent* earthquakes only occur near fault lines or volcanic activity, and earthquakes are usually very rare anywhere else.
Earthquakes can happen anywhere, but from place to place it varies hugely how frequently they happen and how powerful they tend to be. There is a condition for an earthquake to happen, there must be potential energy stored in the stresses of the crust. Where this happens by far the most frequently by many orders of magnitude is along the fault lines, because that’s where all the movement happens. That doesn’t mean you can’t have a strong earthquake in the middle of Eurasian plate for example, it just doesn’t happen very often, in more stable areas there might not be a single notable earthquake in your entire lifetime.
To add on a question-there’s no fault in the New Madrid zone, but there were a series of reaping earthquakes in 1811-1812 that formed Reelfoot Lake in NW TN. Why were there earthquakes there?
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