Generation of the teleseismic P-wave coda from Aleutian earthquakes |
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| Authors: | Charles H Estabrook Michael Weber Rainer Kind |
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| Institution: | GeoForschungsZentrum-Potsdam, Telegrafenberg, 14473 Potsdam, Germany. E-mail: chuck@gfz-potsdam.de;Institut für Geophysik, Universität Göttingen, 37075 Göttingen, Germany |
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| Abstract: | We investigate large-amplitude phases arriving in the P -wave coda of broad-band seismograms from teleseisms recorded by the Gräfenberg array, the German Regional Seismic Network and the Global Seismic Network. The data set consists of all events m b≤ 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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| Keywords: | Aleutian Islands crust seismic coda seismic-wave propagation subduction |
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