Relative moment tensor inversion based on ray theory: theory and synthetic tests

SUMMARY A relative moment tensor inversion is developed for seismic sources belonging to a small source region. The impulsive point-source approximation is assumed to be valid. Input data are amplitudes of low-pass filtered, isolated body-wave phases in the seismograms, and the azimuths and take-off angles of the corresponding rays at the sources. The new aspect of the method is the elimination of Green's functions from the equations. Hence only a minimum of structural information is needed, sufficient to identify correctly phases Pg, PmP, Sg etc. and to determine azimuths and take-off angles. The relative method without reference mechanism is applicable to clusters of seismic sources with different radiation patterns. For source clusters with identical radiation patterns a reference mechanism must be known. The relative method without reference mechanism is studied with synthetic data with regard to additive, Gaussian noise, poor azimuthal station coverage and the resolution of non-double-couple components.

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