Abstract

We investigate the portability of a spectral amplitude method in determining moment tensor solutions for mine‐related seismicity recorded by deep mining networks to tectonic earthquakes recorded by surface aftershock networks. The original methodology inverts spectral amplitudes—with polarity attached—for direct P, SV, and SH waves recorded at deep‐seated geophones, so surface recordings must first be cleaned from free‐surface effects to recover the incident P and S waves. For precritical incidence, the correction is easily achieved by dividing the vertical component of the P and SV waveforms by the corresponding free‐surface reflection coefficients; for postcritical incidence, a more sophisticated correction that accounts for waveform distortion introduced by the coefficient’s phase shift is needed. Correction of SH components is achieved through division by a factor of 2. The proposed corrections are applied to 16 earthquakes recorded at local distances (<10  km) by an aftershock network deployed in the locality of São Caetano, Pernambuco, between 15 September and 23 December 2010. Spectral amplitudes are obtained through a time‐domain technique, and polarities assigned by comparing the corrected seismic pulses with a low‐pass‐filtered delta function. Although interference with the S‐to‐P critical reflection prevented the use of many SV amplitude measurements, inversion of the remaining spectral amplitudes allowed the recovery of deviatoric moment tensors for most of the events. Comparison with an independent first‐motion fault‐plane mechanism developed for the area shows consistency with our moment tensor solutions. Additionally, the ported methodology allows estimation of moment magnitudes for the selected events.

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