Open AccessWave propagation in a multiple‐scattering upper mantle—observations and modelling
Author(s) -
Tittgemeyer M.,
Wenzel F.,
Fuchs K.,
Ryberg T.
Publication year - 1996
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1996.tb04735.x
Subject(s) - coda , geology , mantle (geology) , velocity gradient , seismology , scattering , phase velocity , refraction , geophysics , s wave , group velocity , seismic velocity , seismic wave , phase (matter) , geodesy , physics , optics , mechanics , quantum mechanics
SUMMARY A striking feature of Russian long‐range seismic refraction data from Peaceful Nuclear Explosions is the observation of a high‐frequency teleseismic P n , phase, which travels with a group velocity of 8.0 km s ‐1 out to distances of several thousands of kilometres. Modelling using the reflectivity method shows that this phase can be understood as the response of an upper mantle that contains random RMS velocity fluctuations of about ±4 per cent superimposed on a positive velocity gradient. This class of model explains the existence of the teleseismic P n , its high‐frequency content and its coda length. A teleseismic P n can only be generated if velocity flucluations are strong enough to cause multiple scattering and occur on a subwavelength scale. Cross‐correlation properties of P ‐ and S ‐wave velocity fluctuations exert a substantial influence on the wavefield. A completely unexpected phase can be observed if the fluctuations are imposed on a negative gradient