Use of small earthquake records to determine the source time functions of larger earthquakes: an alternative method and an application

Small earthquake records are increasingly being used as empirical Green's functions to estimate the source time functions (STFs) of large earthquakes. This is generally accomplished in the frequency domain by computing the ratio of the large to the small event spectrum and then transforming it back to the time domain. This study proposes an alternative method in which a large-event STF is approximated by a series of pseudotriangular pulses whose parameters are determined by a nonlinear frequency-domain inversion, involving the spectrum of the large and the small events. The method allows a "positivity' constraint to be imposed on the STF. The misfit between the observed and computed large-event seismograms is measured in the frequency domain over the range of frequency in which the data are reliable. -from Authors