Focal depth is estimated by inspecting broadband waveforms for the presence of depth phases.
Identification of depth phases is aided by visually comparing the observed with synthetic waveforms calculated for a variety of focal depths. An estimate of the source duration is obtained by measuring the width of the P wave displacement waveforms derived from broadband records and by matching the frequency content with synthetics calculated for a number of source durations. Synthetics for any arbitrary shear dislocation source can be quickly derived from the fundamental seismograms and compared with recorded seismograms. Using a logarithmic L 1 norm and a grid search algrithm, the differences between observed and theoretical amplitudes are minimized as a function of seismic moment, fault strike, fault dip and direction of the slip vector. See also the EMSC homepage .