A broadband seismometer records the full range of seismic frequencies. This is exactly what is done on the short period seismogram. When there is a large earthquake, it is usually seen very clearly on the long period seismogram. If there is an explosion at the same time, the broadband record will show the large waves of the earthquake, and superimposed on these waves will be the higher frequency and smaller amplitude waves of the explosion. Filtering the broadband record enhances the energy of interest.
Seismologists describe earthquakes in terms of their intensity and magnitude .
Intensity measures the effect of the earthquake on structures and people at a particular place, whereas magnitude describes the amount of energy released by an earthquake. Intensity scales are qualitative . A widely used standard for judging earthquake intensity is the Modified Mercalli Scale . Intensity scales have serveral limitations. They cannot be used in uninhabited areas because there would be no structures subjected to earthquake damage.