On the possibility of detecting complex sources of earthquakes from data of the centroid moment tensor catalog

In their analysis of the crustal stress-strain state and the study of strong earthquake sources, a number of authors use the parameter ɛ measuring the deviation of the focal mechanism from the double-couple model. Can one obtain reliable estimates of ɛ from regular determinations of the seismic moment tensor components made at world seismological centers and use these estimates to gain constraints on the rupture at the source? Comparing centroid moment tensor solutions of Harvard University with determinations made at the National Earthquake Information Center (United States) and analyzing some strong earthquakes, we arrive at a negative answer to this question. The values of ɛ and the consideration of determination uncertainties in seismic moment tensor components cannot provide a reliable idea of the source complexity, so that independent geological and geophysical information should be invoked.