Fault plane solutions using relative amplitudes of P and surface reflections: further studies

Summary. The method of computing fault plane solutions for small shallow earthquakes using relative amplitudes of P and pP , as described in an earlier paper, is extended to include sP. It is shown theoretically that even a single relative amplitude observation can impose a severe constraint on the orientation of an assumed double couple source, and earthquakes studied in the earlier paper are reprocessed with the inclusion of sP information. The method is also extended to deep earthquakes using long period seismograms, and to undersea earthquakes by allowing for the effect of a sea layer on the surface-reflected phases. Also described are options to search only a restricted range of source orientations, and to identify those orientations which are incompatible with one or more relative amplitudes. These options are applied to several earthquakes, to demonstrate the scope of the relative amplitude method. Results are illustrated using the seismic modelling method of Hudson (1969a, b) and Douglas, Hudson & Blamey (1972).