Publications

We investigate large-amplitude phases arriving in the P-wave coda of broad-band seismograms from teleseims recorded by the Gräfenberg array, the German Regional Seismic Network and the Global Seismic Network. The data set consists of all events mb ≥ 5.6 from the Aleutian arc between 1977 and 1992. Earthquakes with large-amplitude coda waves correlate with the presence of oceanic crust in the source region. The amplitudes sometimes approach those of the P wave, much larger than predicted by theory. Modelling indicates that phases in the P-wave coda cannot be P-wave multiples beneath the source and receiver, or underside reflections, which precede PP, from upper-mantle discontinuities. Among the events, seismograms are very similar, where the arrival times of the unusual phases agree approximately with the predicted times of S-to-P conversions from the upper-mantle discontinuities under the source. Because the large-amplitude phases in the P-wave coda have little, if any, dependence on event depth and have predominantly an SV-wave radiation pattern towards the receiver, we suggest that they originate as SV and /or Rayleigh waves and are enhanced by lateral heterogeneity and multipathing from the subducting Aleutian slab.

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Estabrook, C. H.; Weber, M.; Kind, R. (1997): Generation of the teleseismic P-wave coda from Aleutian earthquakes. Geophysical Journal International, 130, 349-364.