Measuring the fractal dimension of the seismic source through the high-frequency fall-off of source spectra

Using the Wigner-distribution estimation, the high-frequency fall-off of source spectra was estimated. The technique was applied to the analysis of the source spectra of the July 22, 1994, Vladivostok M6.4 deep-focus earthquake and that of the July 22, 1994, Northern Japan Sea M5.7 deep-focus earthquake. It is shown that the high-frequency fall-off of the source spectra of these two earthquakes may be characterized by two parts. Between the first corner frequency f1 and the second corner frequency f2, the high-frequency fall-off of the source spectra can be represented by f5.0: above f2, the high-frequency fall-off can be represented by f1.4. In the perspective of the fractal geometry of earthquake source, it seems that the deep-focus earthquakes under consideration may be characterized as being composed of some 'sub events'. On the other hand, each sub event has its complex structure. (author). 12 refs, 3 figs, 1 tab