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[EarthNSky <erthnsky AT bellsouth.net>]

It is the type of fault.  I believe that before Northridge, we did not
know much about blind thrust faults.  They had to create a way to find
them, and they are still finding them, most disturbingly under largely
populated areas-usually valleys.  I got the following off Wikipedia, 
which has a good intro page on Blind Thrust Faults:

> If the region is under active compression, these faults are
> constantly rupturing, but any given valley might only experience a
> large earthquake every few hundred years. Although usually only a
> Magnitude 6 or 7 earthquake, it is especially deadly because the
> seismic waves are highly directed, and the soft basin soil of the
> valley can amplify the ground motions by over a factor of 10.

That soft basin soil is also subject to liquifaction in some cases, and 
we saw that at Northridge and Kobe, both blind thrust quakes.
The acceleration rate is because it is literally under foot and the 
waves are compacted and funneled, like a tsunami as it nears shore.

I probably shouldn't have picked the Northridge quake in my 'imagine' 
post because that kind of quake doesn't get much bigger than a 7, but 
for a lot of folks in SoCal, that was 'the big one', at least the 
biggest one they have experienced, *and* that was the one that Gene had 
mentioned.

Bev




Lynda wrote:
> Northridge was different and is "special" in its own right.  It had
> the highest acceleration rate ever recorded.  It was the actual 6.7
> that was the culprit in that instance.


--
BevanRon of EarthNSky Farm   NW Georgia USDA Zone 7
34.498N 85.076W    Bev is Earth, Ron is Sky