Seismographs and seismograms

As all seismograms are filtered versions of ground motion they cannot be interpreted without knowing the filter response. Analysts will know roughly from simple inspection of a seismogram how the ground motion has been filtered when the response is unspecified: LP seismograms show quasi-sinusoidal signals with a period of a few tens of seconds; SP seismograms often show signals as wavelets of ˜ s period and broad-band signals may be pulse-like. The effect is illustrated with synthetic seismograms in Figure 4.1 for amplitude responses shown in Figure 4.2. For quantitative interpretation and analysis, the response must be known.