re: hey 2(Davin): P & S waves
I've looked at copes of the seismographs (sp?) the temporal gap is around 10 seconds. It is consistent with the known subsurface geology of that area. Nearly all the original reporters of the 'second explosion' said "about a dozen seconds later" when talking about the timing of the second blast that "they fealt a rumble". Subsequent reports by other people who go on the record years later have different stories.
note that I felt the blast many miles away.
Davin L.