Theoretical investigation of the excitation of leaky modes for
multi-layered models
Abstract
With the advent of the array-based methods, the observations of leaky
modes from earthquake records and ambient noise are frequently reported.
It is urgently needed to have an effective guide to the selection of
certain leaky modes to put into practical inversion combined with other
imaging methods. To this end the excitation of leaky modes for
multi-layered models is theoretically investigated. By computing
theoretical seismograms for different source mechanisms and different
source depths with the discrete wavenumber method and the normal-mode
summation method separately, the contribution of leaky modes to the
resultant seismograms is qualitatively evaluated and the effect of the
source depth for the same source mechanism is in detail examined.
Further, we perform accurate computation of leaky modes for two models
and categorize the leaky modes into PL and OP (organ-pipe) modes, whose
distinctive properties are characterized both from the attenuation and
from the eigen-displacements of these two types of modes. Also, these
results could help explain very well the occurrence of certain leaky
modes on the dispersion spectrum and be indicative of the reasonable
choice of certain leaky modes to put them into practical inversion for
P-velocity structures.