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An introduction to surface waves.
Continuation of the Introduction

Dispersion and dispersion analysis:

In homogeneous halfspace, surface waves have no single apparent velocity for all frequencies, but have an apparent velocity that is a function of frequency. The Love and Rayleigh wave are then called dispersive. Thus, we can define two velocities, the envelope's velocity or group velocity and the carrier velocity or phase velocity.

Studying of surface wave dispersion curves based upon seismological observations at the Earth's surface can inform us about the velocities at depth. Dispersion data are used to study more complicated velocity structures, such as the following example on the Kerguelen hotspot:

Fig. 5: Results of dispersion analysis of event 93_216, showing the logarithm of the square root of the energy for the three components as a function of group velocity and period. The maximum energy is shown in red.

Fig. 6: Group velocity curves for the three components of the same event 93_216, defined by the maximum of energy at each period.

In this example, we could infer from the presence of a transverse component for the Rayleigh wave that only a specific anisotropic model could fit the dataset. Read more about the example of the Kerguelen hotspot here.

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