Time- and frequency-dependent polarization analysis: anomalous surface wave observations in Iberia

Abstract

A time- and frequency-dependent polarization method is applied to synthetic and observational data in order to investigate effects of lateral heterogeneity on surface wave polarization. It is shown that interference of surface wave signals can produce artifacts in the polarization as determined for the dominant signal present in the data. The time- and frequency-dependent polarization technique is applied to surface waves recorded in Iberia to investigate the character of the recorded wavetrains. Rayleigh waves with a southwest backazimuth recorded in the south of Spain appear strongly attenuated relative to other locations in Iberia. By analysing their polarizations, it can be inferred that these surface waves are highly distorted, implying that scattering mechanisms must be operative in the south of Spain. Strong scattering is one of the mechanisms that might explain the observed amplitude reduction, although other mechanisms like intrinsic scattering or defocusing may also contribute. With the present data and the present technique it is not possible to determine the relative contributions of each of these mechanisms.