The word "earthquake" explains this phenomenon - the earth shakes.
Indeed, during the earthquake rumbles and shakes the ground, cracking the ground, houses collapsing, falling pillars, overturn trains, erased from the face of the earth the entire city. Scientists estimate the magnitude of the earthquake in points. The more powerful its destructive power, the higher the score. The highest score 10-12 points, the average is 3-4. Often quite weak shocks, which almost unnoticed by man.