Pocket Earthquake is a funny quake simulator based on real physics, it will show you how a four story building behaves when it's hit by your hand motion. It's very simple, try it out!

Instructions:

1. Move your device left and right and see the building shake.
2. To change parameters, double tap the screen.
3. Double tap again to see the building move with the new parameters set.

The science behind it:

ag = acceleration impressed at the base of the building (we assume that your hand shakes the ground)
T = quake period
T1 = first modal period of the structure
T2 = second modal period of the structure
Modal multipliers = increase the effect of a particular vibration
ξ = this is the damping factor (an increase of ξ would dissipate the quake's energy better)

For those familiar to seismical analysis, Pocket Earthquake will be interesting to help you understand the way a building should be made to resist different kind of seismic inputs.