Inversion for the Composite Moment Tensor

The composite moment tensor is defined in analogy to the composite focal mechanism as the averaged representative seismic moment tensor characteristic for a focal area under study. In contrast to the composite focal mechanism, which provides information on shear faulting, the composite moment tensor can provide additional information on nonshear rupture mode and on physical conditions along the fault. The composite moment tensor is calculated by a joint inversion of multiple earthquakes associated with the same fault system and displaying a similar focal mechanism. The method utilizes amplitudes of P and/or S waves or full waveforms. Because the inversion is linear, it is fast and applicable to datasets of many earthquakes. The method is particularly suitable for the analysis of microseismicity, earthquake swarms, or aftershock sequences, where observations of multiple earthquakes are available. The composite moment tensor can be retrieved even when the station configuration or data quality prevent inversion for the full moment tensors of individual earthquakes.