Hi, Quendi!!
I'm wondering whether the information you read, was discussing the phenomenon roughly called "unzipping" of faults...
If a fault line "unzips" in granite, as opposed to "unzipping" in sandstone/shale/limestone, I would think that the tougher rock - granite - would tend to 'dampen' the vibratory effect of the quake - a subsurface similarity to what happens on the surface between sand/landfill/high water table liquifaction-prone ground, and ground underlain by much more solid bedrock...
However, if you find info from the USGS that states that an earthquake originating in granite would be more destructive than one originating in, say, sedimentary rock, I would LOVE to read that!!
One other point - to say that a fault will "unzip" in granite is usually not possible, unless we're talking about an earthquake originating on a fault line in the Canadian Shield area, for example. I make that statement because the earth's crust isn't really homogenous - it's a combination of many types of rock, frequently all jumbled together...
Another factor - it would probably take far more stored energy - force - to generate an earthquake along a 'stuck' fault in a granitic 'shield' area, as fault lines in granitic rock are probably less 'lubricated' - again, as opposed to sedimentary rocks, which will crumble and give way much faster and more easily than granitic rocks... Which would increase the frequency of quakes [in sedimentary rocks or rocks that crumble more easily], but would probably reduce the intensity, because the stresses causing the quake would not be able to build up [to an extremely high, dangerous level...] before the fault line 'snaps', and the pressures are released by crumbling, snapping rock.
And THAT may be what you read about...??
Also, to say that the 'basement' rocks are "all" granitic or "all" sedimentary - that hypothetical situation is LESS likely - but this ALSO depends on the depth at which the earthquake originates - because, if we're talking about relatively "shallow" earthquakes, their point of origin would probably occur in MIXED rock...
But there again, it depends on where the earthquake originates... An earthquake that originates along the Death Valley Fault system, for example, could occur at depths of up to 9,000 feet - almost two miles - and still occur in the sediments filling the valley. Of course, along that fault line, most earthquakes WILL occur due to movement in the underlying bedrock - but just using that as an example that the depth that the earthquake occurs may determine the type of rock that the 'break' or movement occurs in...
Phew! I hope that was clearer than mud...
About earthquakes in general... As you stated earlier, many people don't realize that they're actually living in an earthquake-hazard zone. But while we're on the subject, the science of seismology - "fault-finding" - [I COULDN'T resist that one!!] - is not so far advanced as to be able to determine where ALL the faults are, or for that matter, exactly when the fault line - more accurately, fault line SEGMENT - last 'broke' or moved or generated a significant earthquake... [Mind you, using carbon 14 and argon dating and other methods, they can usually get a pretty good idea...]
But that's if they realize that the fault line is THERE.... Sometimes no one knows that there's an active or dangerous fault line present [though this is happening less frequently, nowadays, as the science of seismology advances...]
So, for someone living in, uhm, well, I'm going to pick on the "Canadian Shield" again, which is somewhat more stable than many other areas of the planet. For someone living on the "Canadian Shield" area, there might be a significant fault line that no-one has discovered yet, that becomes 'unstuck' and generates a significant earthquake...
Humans tend to 'play the odds', regarding natural disasters; but personally, I'd have a LOT more respect for the human race if we as a whole would build all structures on Planet Earth as "earthquake-resistant".
You'll notice that I didn't say, "Earthquake-proof".... In my opinion, the only dwelling that could possibly be considered semi-earthquake-'proof', would be some sort of tent - perhaps a yurt - except that one would still have to deal with falling wooden cross-beams that support the tent.
But at least it would be better than having to dig out from under tons of masonry...
Zid
