Open AccessGuided wave propagation in laterally varying media ‐ II. Lg ‐waves in north‐western Europe
Author(s) -
Kennett B. L. N.,
Mykkeltveit S.
Publication year - 1984
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1984.tb02854.x
Subject(s) - geology , seismogram , seismology , graben , attenuation , refraction , rayleigh wave , azimuth , geophysics , transverse plane , wave propagation , microseism , amplitude , tectonics , physics , optics , structural engineering , engineering
Summary.Lg ‐wave observations at NORSAR from a sequence of explosions straddling the Central Graben in the North Sea, show that the phase is almost extinguished by passing through this structure. For models of the graben structure, based on seismic refraction experiments, with crustal thinning beneath a zone of thickened sediments, numerical modelling of Lg propagation shows very poor transmission. The inclusion of attenuation simulating the effects of scattering from faults and other complex structures further diminishes the transmittivity. The theoretical effect of a crustal pinch is to redistribute S energy over a wide range of groups velocities, a pattern that fits well with the observations. Three components recordings at NORSAR of explosive charges fired in water covering a wide range of azimuths, show significant transverse components to the seismograms. The transverse energy builds up with travel time and for Lg is of the same order as the vertical component. These results are consistent with the theoretical prediction of progressive net transfer of energy from Rayleigh to Love modes as the wavetrain propagates through a three‐dimensionally heterogeneous medium.