SPICE-Research Training Network - UiO > Polarisation anomalies
An introduction to polarisation anomalies:
Usual polarisation of seismic surface waves:
Love waves result from SH waves trapped near the surface, with lateral motion. Rayleigh waves are a combination of P and SV waves, with vertical and horizontal motion. In the far-field, the Rayleigh waves are therefore polarised in the vertical and longitudinal directions and the Love waves in the transverse direction in laterally homogeneous structures. Although most observed seismograms obey this simple rule at first order, some recordings of surface waves present a different polarisation. When a seismic wave deviates from its usual polarisation, it is called a polarisation anomaly.
Possible causes for polarisation anomalies:
These deviations may be ascribed to:
- Local heterogeneities in the structure (isotropic or anisotropic).
- Anisotropy in the structure.
- Large-scale heterogeneities resulting in path deviation from the great circle.
They can be used to infer some of the Earth's properties, as complement to more traditional tomographic studies. Here is an example of how surface wave polarisation anomalies have been used to study the structure near the Kerguelen hotspot.
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