  The power spectral density (PSD) function is commonly used to specify
seismometer performance. It is derived from the FFT of acceleration and
correction is made for the transfer function of the instrument that generated
the data. As with any such spectrum of density (`per Hz') type, the noise
inherent to a PSD is large. This article illustrates the value of a function
that is derived from the PSD and for which the influence of noise is
significantly reduced. Called the cumulative spectral power (CSP), it is
obtained from the PSD through the noise-reducing process of integration. The
maximum of the CSP (corresponding to the longest graphed value of the period)
provides a means for estimating the total vibrational power of the earth. The
present author has significantly simplified the process of PSD generation. Thus
routine graphing is straightforwared-of first the FFT, followed by the
generation of both a PSD and its associated CSP. The unique properties of the
CSP make it valuable for the study of a variety of earth dynamics. For example,
the strking simplicity of a CSP graph generated from a record containing a
strong teleseismic earthquake is undoubtedly important to the development and
refinement of any viable theory of earthquake dynamics.
