What does the red mean?

[v0031]

What is an earthquake?
An earthquake is what happens when two blocks of the earth suddenly slip past one another.
Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. The largest, main earthquake is called the mainshock. Mainshocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the mainshock. Depending on the size of the mainshock, aftershocks can continue for weeks, months, and even years after the mainshock!
Can scientists predict earthquakes?
No, and it is unlikely they will ever be able to predict them. Scientists have tried many different ways of predicting earthquakes, but none have been successful. On any particular fault, scientists know there will be another earthquake sometime in the future, but they have no way of telling when it will happen.

[Tender Branson]

That's a good question: I'm not a native English speaker too, so I would be interested as well.

I think it has to do with the faults like this one:

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

So, it could mean that "scientists expect earthquakes at any of these fault's locations".

But it could also mean "With the possibility of an error by the scientists ...", because fault also means "error" or "liability".

But I guess the first one is meant.

[Adam Griffin]

"On any particular fault" would be the same as saying, "On every fault", "on each fault". It is just a way to make it sound more scientific in some regard; it is to say out of all possible choices, the result (an earthquake) would be the same (it will happen at some point).

To rephrase the entire sentence, "Scientists know that there will be an earthquake on every fault sometime in the future, but have no way of telling when it will happen".

And yes, 'fault' here is definitely referring to geology.

[v0031]

Thank you, very good help.

[muon2]

I would add that as a piece of science writing it has a glaring weakness, one that perhaps is at the root of this thread. The first paragraph is written for a level of reader that knows nothing about earthquakes, and goes into the definitions of the geological terms involved. These include earthquake, foreshock, mainshock, and aftershock. In the second paragraph the weakness occurs when the writer forgets the reader and fails to define fault as a geological term. This is particularly bad because of the alternate meanings for the word fault.