I remember reading a Daedalus column (a New Scientist magazine regular presentation of mostly crazy and impractical but always thought-provoking and entertaining inventions) proposing a distributed continent-wide seismic weapon consisting of a million or so suspended concrete blocks together with systems to calculate the timing and coordinate the release of the blocks so as to focus the resulting wave at any given point on the earth's crust... the chinese version would simply consist of a billion people with stopwatches jumping off chairs at their appointed times.

Giovanni