What is an Earthquake?

• Earthquakes are measurable ground motions of the earth body and generate seismic oscillations. These are oscillations which can cause heavy destructions depending on a certain intensity.
• One distinguishes space waves and surface waves.
  Space waves are the so-called "P" (Primarily) waves. Surface waves are the "S" or secondary waves.
• Space waves propagate faster than surface waves.
• The speed of the P wave is approx. twice as fast as those of the S wave.
• With it the P wave reaches the system location always first.
• P waves predominantly effect a vertical impact. The P wave causes no damage and is imperceptible for people. Animals feel this P wave.
• The S wave is a horizontal oscillation – like a water-wave – and causes damage. The S wave is perceived by the people with fright.

One can say: Earthquakes warn about themselves!