Python codes to compute SC functions and dv/v measurements (Viens et al., 2018, JGR)

Description:

This repository contains Python codes for Viens et al. (2018, JGR). The single station cross-correlation (SC) functions for all the MeSO-net stations between February 20, 2011 to May 11, 2011 can be downloaded at: https://doi.org/10.7910/DVN/TPDPHA

This repository contains:

• The Codes folder:

  • Plot_CC_dv_example.py: To compute dv/v measurements from the data and plot results (the data can be downloaded here). This code uses:
    • Stretching.py: a function to compute dv/v measurements with the stretching method.
    • Additional_Functions.py: Additional functions to plot the data.
  • Get_SC_functions.py: Main function used to compute single-station cross-correlation (SC) functions.

• The Data folder:

  • Empty folder. SC functions can be downloaded at here.

• The Figures folder:

  • To save the figure from the Plot_CC_dv_example.py code.

Example:

The figure from the Plot_CC_dv_example.py code when applied to the SC functions calculated at the NS7M MeSO-net station is shown below. SC functions are computed over 15-min data for the Z-N and Z-E components and subsequently stacked over 6 hours. The reference waveform is the stack of the SC functions between Feb. 20 to March 10th, 2011 (e.g., before the 2011 Mw 9.0 Tohoku-Oki earthquake). The SC functions are bandpass filtered between 1 and 20 Hz and the stretching is performed on the first second of the SC functions.

• The top subplot shows the correlation coefficient between the reference waveform and each current window. A correlation coefficient equal to 1 indicates that the two waveforms are perfectly symmetric. Note that the CC for the Z-N and Z-E SC functions are averaged following Hobiger et al. (2014, GJI).
• The bottom subplot shows the dv/v measurements averaged over the Z-N and Z-E SC functions following Hobiger et al. (2014, GJI). Dark red circles indicate high correlation coefficients and white/yellow colors indicate low correlation coefficients. The large drop of dv/v on March 11th, 2011 is caused by the Mw 9.0 2011 Tohoku-Oki earthquake. The small drop in February is caused by a precipitation event. Note that the figure below is a little bit different from that of the paper (e.g., Figure 7) as the maximum dv/v change allowed when performing the stretching is set to 10%.