ABSTRACT
The empirical Green’s function deconvolution technique in the frequency domain is used to retrieve the source time functions from the records of P waves from seven seismic events that occurred at a copper mine in Poland in 1998. The events were located within the underground seismic network composed of 32 vertical sensors. Their moment magnitude ranged from 2.7 to 3.2. The records of smaller events from the same area and with similar source mechanism, with moment magnitude ranging from 2.2 to 2.4, were accepted as empirical Green’s functions. The relative source time functions retrieved at several stations display directivity effects in five cases, implying unilateral rupture propagation. The azimuth of the rupture propagation direction and the rupture velocity were estimated from the distribution of pulse widths and pulse maximum amplitudes as a function of the cosine of station azimuths. The rupture velocity was variable, ranging from 0.33 to 0.88 of the shear wave velocity. The source dimensions, represented by the fault length, are rather small in comparison with those estimated in the frequency domain; they range from 130 to 540 m. The source pulse widths were found to be about twice smaller than the reciprocals of corner frequencies, and the rupture velocity is lower than that usually accepted in spectral models of seismic sources.
