sidereal.py is a short python code that can be used to apply a sidereal filter (SF) to 30 sec position time series according the method described in Twardzik et al. (2019).
The code uses 30 sec kinematic position time series (XXXX.k.tdp). It takes the positions before a given large earthquake to build the sidereal filter. From experience, 6 days prior the earthquake are needed to build a robust filter. The SF is built by optimally shifting and stacking the days before the earthquake using cross-correlations. By doing that, the aim is to enhance the signature of multipaths and overcome the issue of using a constant constellation throughout the processing. Once built, the SF slides along the time series and is applied in order to remove the multipaths over the full time series.
[date]: Dates of the positions in a datetime format.
[time]: Epoch of the positions (seconds). It is assumed that the positions are given with respect to the first epoch in the time series. Thus, the first epoch is assumed to be zero.
[eq]: Date of the main earthquake in a datetime format. It is possible to act like there is no earthquake by setting [eq] to some time in the future.
[showme]: When set to True, it displays the stacks and the obtained filter. Very useful to determine if there are indeed some repeating signals worth removing.
[1] This code has not been optimised and I do not guarantee that it is bug free when using it on your own time series with their own particularities. Use it at you own risk.
[2] This code has been developed for 30 sec position time series, so I do not guarantee that it provides meaningful results for shorter or longer sampling interval.
[3] Please cite Twardzik et al. (2019) when the code has been used for publication (doi:10.1038/s41598-019-39038-z).
[4] The code does not handle foreshocks and aftershocks. It acts as if there is only one earthquake.
[5] The code uses standard libraries with the exception of the xcorr function which is taken from obspy (doi:10.5281/zenodo.1040770).