Abstract

A relative moment tensor inversion technique is used to retrieve the focal mechanisms of teleseismic earthquakes. The observed data consists of amplitude spectra of the direct P phase on vertical and the direct S phase on rotated horizontal components. The effect of propagation paths is minimized using relative amplitude spectra of close-lying earthquakes recorded by common stations. The inversion is carried out for six components of the moment tensors. The focal mechanisms are determined using a linear weighted least-squares approach (signed spectral moment). The method is applied to seven earthquakes that occurred close to the 26 December 2003 Mw 6.6 Iran-Bam earthquake and were recorded at regional–teleseismic distances with good azimuthal coverage. Most focal mechanisms obtained in this study show a predominantly right-lateral strike-slip component, similar to those obtained by other independent estimates. The application of the relative moment tensor inversion using spectral amplitudes combined with polarity data proves to be flexible and effective in estimating focal mechanisms of teleseismic data and the method is suitable for routine implementation in seismic networks.

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