Preliminary determination of focal mechanisms from the inversion of spectral amplitudes of mantle waves

We present a method for the preliminary determination of focal mechanisms ( PDFM). based on the inversion of deviatoric moment tensor components from d epleted datasets of mantle wave spectral amplitudes. The latter are found t o be largely insensitive to errors in epicentral estimates, which can hampe r the inversion of the full complex spectrum under real-time operational co nditions. Robust solutions can be obtained from Rayleigh wave spectra at as few as three stations, and from a combination of Rayleigh and Love waves a t only two stations, provided they sample 60 degrees in azimuth. The system atic application of this method to a dataset of 43 large earthquakes during 1996-1999 yielded mechanisms rotated an average of only 17 degrees from th e published Harvard CMT, a figure comparing favorably with the case of othe r catalogues, such as the USGS moment tensor solutions. (C) 2000 Elsevier S cience B.V. All rights reserved.