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Observations of shear‐coupled P waves
Author(s) -
Zandt George,
Randall George E.
Publication year - 1985
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl012i009p00565
Subject(s) - seismology , seismogram , lithosphere , geology , classification of discontinuities , shear waves , amplitude , discontinuity (linguistics) , crust , reflection (computer programming) , geophysics , shear (geology) , seismic wave , longitudinal wave , p wave , mantle (geology) , love wave , wave propagation , mechanical wave , tectonics , physics , petrology , optics , medicine , mathematical analysis , mathematics , computer science , cardiology , programming language , atrial fibrillation
Teleseismic SV waves couple to P waves in the lithosphere in several ways. P waves converted from discontinuities in the lithosphere precede the main SV arrival as small amplitude Sp precursors. Large amplitude P waves follow the main SV arrival after conversion by reflection at the free surface, and post‐critical reflection from a discontinuity in the lithosphere. SPdiff denotes a converted P wave diffracted along the underside of the crust when a teleseismic SV wave strikes it from below near the critical angle of incidence. We observed several of these shear‐coupled P waves on seismograms of deep earthquakes recorded at broadband seismic stations (RSTN) in North America. For these paths, large amplitudes relative to SV characterize the lithospheric multiple near 50°, with amplitudes decreasing rapidly beyond 60°. Calculation of synthetic seismograms indicate that a post‐critical reflection from a discontinuity at 70‐80 km depth where compressional velocity increases abruptly to about 8.5 km/s produce the largest amplitude P arrival. The observations of these shear‐coupled P waves presents a previously untapped source of information about the fine structure of the upper mantle.