P-SH conversions in a flat-layered medium with anisotropy of arbitary orientation

V. Levin, J. Park

Research output: Contribution to journalArticlepeer-review

173 Scopus citations

Abstract

P-SH conversion is commonly observed in teleseismic P waves, and is often attrbuted to dipping interfaces beneath the reciever. Our modelling suggests an alternative explanation in terms of flat-latered anisotropy. We use reflectivity techniques to compute three-component synthetic seismograms in a 1-D anistropic layered medium. For each layer of the medium, we prescribe values of seismic velocities and hexagonally symmetric anistropy about a common symmetry axis of arbitrary orientation. A compressional wave in an anisotropic velocity structure suffers conversion to both SV-and SH-polarized shear waves, unless the axis of symmetry is everywhere vertical or the wave travels parallel to all symmetry axes. the P-SV conversion forms the basis of the widely used 'reciever function' technique. The P-SH conversion occurs at interfaces where one or both layers are anisotrpic. A tilted axis of symmetry and a dipping interface in isotropic media produce similar amplitudes of both direct (P) and converted (Ps) phases, leaving the backazimuth variation of the P-Ps delay as the main discriminant. Seismic anisotropy with a tilted symmetry axis leads to complex synthetic seismograms in velocity models composed of just a few flat homogeneous layers. It is possible therefore to model observations of P coda with prominent transverse components with relatively simple 1-D velocity structures. Successful retrieval of salient model characteristics appears possible using multiple realizations of a genetic-algorithm (GA) inversion of P coda from several backazimuths. Using GA inversion, we determine that six P coda recorded at station ARU in central Russia are consistent with models that possess strong(> 10 per cent) anisotrpy in the top 5 km and between 30 and 40 km depth. The symmetry axes are tilted, and appear aligned with the seismic anisotropy orientation in the mantle under ARU suggested by SKS splitting.

Original languageEnglish (US)
Pages (from-to)253-266
Number of pages14
JournalGeophysical Journal International
Volume131
Issue number2
DOIs
StatePublished - 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

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