> This will be interesting on an academic level because of the transmission of
> high frequency ground motions versus low frequency ground motions and the
> in-structure response. The 20th floor of a building should not transmit a
> significant high frequency ground motion, but would transmit low frequency
> ground motions.
> The underlying rock of the East Coast is not highly fractured as the classic
> slip faults in California. The ground motions (especially low frequency) do
> not attenuate quickly in unfractured rock. This is the 20th earthquake of
> Modified Mercalli V or higher in Virginia since 1774. There was a Modified
> Mercalli VIII in 1897 in Virginia.
> My son serves on an aircraft carrier, but is living on shore now in Norfolk,
> VA. He felt it, but was not too alarmed.
> ...The aircraft carrier sustained no damage;>)
> Regards, Harold Sprague
Harold, you are all right when focused on lateral motion, as most of seimic engineering seems to be.
But if your quake happens to have a strong vertical component, the building will be transmitting
high fequency as well, vertically.
Gregory from Oz