Tuesday, April 16, 2013
M7.8 Earthquake Iran
This is set in an area of pure compression, as the African Plate and Indian both jam up.
And therefore, we get a 'beachball' of pure compressional thrust. Very shallow. Most likely this was a 'super quake', similar to Kobe or Armenia. That is when the fault rupture velocity exceeds the shear wave velocity, and essentially forms a shock wave of compression. When that hits the surface, rocks fly in the air, and the PGV probably exceeds 2 m/s. Nobody has been around to actually measure one of these things, so we don't know.
Update: Pooey! The beachball shows normal faulting. Always get that wrong! Forget the super-quake then, it's just average, which is enough to knock all the rubble houses down.
Update2: I take that back. A shallow thrust super-quake could totally screw up the beach! I would have to double-check Armenia, if I wanted to do work. :)
Update3: Blah, deep extension earthquake, with no PGV. This area is like the Sea of Japan, being wrenched apart by 2 plates with different vectors.