Source pulse enhancement by deconvolution of an empirical Green's function

Observations of the earthquake source-time function are enhanced if path, recording-site, and instrument complexities can be removed from seismograms. Assuming that a small earthquake has a simple source, its seismogram can be treated as an empirical Green's function and deconvolved from the seismogram of a larger and/or more complex earthquake by spectral division. When the deconvolution is well posed, the quotient spectrum represents the apparent source-time function of the larger event. This study shows that with high-quality locally recorded earthquake data it is feasible to Fourier transform the quotient and obtain a useful result in the time domain. In practice, the deconvolution can be stabilized by one of several simple techniques.

In this paper, the method is implemented and tested on high-quality digital recordings of aftershocks of the Jan. 9, 1982 Miramichi (New Brunswick) earthquake. In particular, seismograms from a Jan. 17 aftershock (017 13:33 GMT, local mag.=3.5) exhibit path or site effects which complicate the determination of source parameters. After deconvolution, the apparent far-field source of this event is a simple pulse in displacement with duration ≈ 0.07 second for both P and S.