"What was the cause of the northridge earthquake?"?

Question

"What was the cause of the northridge earthquake?"?

Answer 1

OK, "dreamofdiversity" is all very clever citing "blind thrust fault" from Wikipedia.

It might be more helpful to know that a "thrust fault" is a particular type of low-angle (sub-horizontal) fault running under the surface.  "Blind" means that it locally terminates (or "tips out") under layers of shallower rock (although many thrust faults do eventually reach the surface).

But in the case of the Northridge fault, unlike the sub-vertical San Andreas Fault, being a blind thrust meant it is invisible from the surface.  That is, until it moved, at which point its effects were certainly felt!

The San Andreas fault is caused by two "plates" of rock moving sideways past each other.  A thrust fault moves by having one slice of rock sliding up and over another slice of rock.

Answer 2

blind thrust fault