The CC contains velocity dispersion information (group/phase velocity) about the medium traversed by surface waves (the ambient seismic noise is mainly constituted by surface waves, see the previous article) between each station pair. Once the dispersion information is extracted, it is possible to apply seismic tomography to obtain corresponding group and phase velocity maps.
For the extraction of such information most commonly is used the CC’s symmetric component but also the raw data or just the acausal/casual components can be used (the decision to use one of them is strictly dependent to the ambient seismic noise and the CC’s waveform characteristics). An example of the above processing in its total can be seen in one of my pubblication which can be accessible from HERE.
The steps to extract group/phase velocity are synthetized below:
- For each CC, you must decide what component to use (it can be the raw waveform, the symmetric component or just the a-casual or casual part of the waveform)
- Input all the selected CCs components from the previous step into the program to compute the group velocity dispersion using different algoritm and then validate it.
- The “average” group velocity dispersion curve, (output in the previous point), is going to be used as “corridor” for the semi-automatic phase velocity picking .
- At this point, as last step, you must validate the phase velocity dispersion extracted. Just the results that satisfied certain “error” criteria are going to be considered and then potentially used for the further computations which is the tomographic inversion.
You can download from below a script package to compute automatically what I described above (if not avaiable it is still a work in progress).