Fault plane solutions using relative amplitudes of P and pP

One way of finding the fault plane orientations of small shallow earthquakes is by the generation of theoretical P-wave seismograms to match those observed at several distant stations. Here, a technique for determining the uniqueness of fault plane solutions computed using the modelling method of Douglas et al. is described. Relative amplitudes of P and pP, and their polarities if unambiguous, are measured on the observed seismograms to be modelled, and appropriate confidence limits are assigned to each measurement. A systematic search is then made for all fault plane orientations which satisfy these observations.