[log in to unmask] wrote:
>  
> It is also perplexing to see fallen sections of 10 meter high elevated 
> concrete roadway which seem to have pancaked straight down, intact, 
> but the cars are uniformly flipped over.  Of course that may be simply 
> the most dramatic image.


What I learned from an article is that the shaking is different, 
depending on what type of fault you are on - thrust fault, or 
strike-slip. I may have this backwards, but here goes. Strike-slip is 
two plates trying to move past each other along a butted edge. When the 
pressure is released one plate slides one direction, the other plate 
slides in the opposite direction. The shaking and waves are lateral, 
causing back and forth, sideways shaking. There is some vertical 
movement, like riding waves at the beach, but most of the movement is 
from side to side.

Thrust faults rupture as one plate rises and another one sinks. The 
shaking is vertical, up and down. That's why the road pancaked straight 
down and the cars were flipped, probably. Apparently you can put 
"springs" in the bottom of a tall building and it will survive the 
vertical moves, with the energy absorbed into the "springs."

When the shaking is side to side at the base, the building is like a 
pendulum, the arc described at the top being similar to the bottom and 
maybe cracking off at the center of the "X". Again, I'm no expert and 
was only really able to form general ideas, not understanding a lot of 
the math.

~deb
>  

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