3.3. Measures of earthquake size and shaking intensity
Part of the deformation energy which is released during an earthquake is released in form of seismic waves which, depending on the strength of the excitation, can propagate over large distances and in extreme cases even cause the whole globe to resonate. Nowadays, thousands of seismic sensors worldwide continuously record the movement of the ground. The output of these sensors (which usually operate in three perpendicular spatial directions) is digitized and either stored locally and subsequently collected or directly transmitted to an analysis center where it provides the basis for the detection and the determination of the source parameters of seismic sources.
The most basic source parameters of earthquakes are their locations which are determined from the arrival times of seismic waves, and different measures of the earthquake size (referred to as magnitudes) which are determined from the amplitudes of seismic waves, measured on different types of instruments.