A method is devised to measure body wave dispersion in terms of the arrival time of a narrow band-pass filtered signal. The arrival time is defined as the expectation of the arrival time of the wave front minus half the duration of the first pulse. Body wave dispersion is related to an absorption band, and its transfer function is found. By interpreting the absorption band as a filter and identifying the dispersion as the (frequency dependent) group delay of the filter the measured dispersion is interpreted as due to a cascade of filters composed of the following elements: intrinsic attenuation, source time function, and finiteness of the fault. ¿American Geophysical Union 1991