NDCP

Noisy Dispersion Curve Picking

Suite package to pick velocity group dispersion curves of surface waves from noise cross correlation data and earthquakes, Version 1.0

INPUT FILES:

NDCP handles data in SAC format (https://ds.iris.edu/files/sac-manual/manual/file_format.html ). Data must be placed in a same folder. SAC header must contain Station and Event information (latitude, longitude, origin time of the record and of the earthquake if the case). To avoid border effects at long periods filtering (especially for earthquakes records), we suggest to add a broad time window (around 20-30% of the earthquake duration), before and after the seismogram.in the case of CC data, a lag time of at least three times the expected arrival time of surface waves is suggested.

TO RUN NDCP:

1. set the path of the NDCP folder in the matlab environment
2. execute the main script p1_NDCP.m
3. select the data type and select the data folder in the popup window
4. select whatever file, NDCP will read all the SAC files inside the folder.

DEFINING FTAN PARAMETERS: When a file is selected, NDCP reads and displays the Waveform and Amplitude Spectrum. pre-defined FTAN parameters: Distance (km): directly read from the SAC HEADER

Tmin (s): minimum period to be analyzed Tmax (s): maximum period to be analyzed fstep log(s): step (distance in seconds) between two consecutive filters width log(s) length of the filter window filter order: order of Butterworth filter Cut signal(s): option to select a subset of the displayed data (put nothing if the whole signal is kept)

Default values are automatically calculated depending on the station-station or event-station interdistance. User can modify it if needed.

Once the parameters are defined, NDCP will calculate and display the FTAN analysis for each record:

• FTAN waveforms of Seismic record, at top left.
• Seismic record, at bottom left.
• Velocity-Period diagram, at bottom right.
• FTAN envelopes for picking dispersion curves, at top right.

PICKING OF THE DISPERSION CURVE:

1. Let choose the picking preference: REPEATED CLICKS (clicking several points) or CLICK&HOLD (one click and hold the mouse).
2. Let click on PICKING OF DISPERSION CURVE BUTTON. In the case of cross correlation data, user has to select the part of the signal to be picked (causal or anticausal). for CC data users can pick, only one branch or both by selecting them one per time (both curves will be saved). If user needs to modify the picking, can do it just selecting once again the button PICKING OF DISPERSION CURVE BUTTON” ( for records) or causal/non causal ( for cross correlations). by default only one dispersion curve per signal is picked. If the user wants to pick various parts of the same dispersion curve on the same signal, has to select the button “segmented picking”. This option allows the picking of dispersion curves with gaps in the middle or even other parts of the signal (e.g. superior modes etc.).
3. If REPEATED-CLICKS option was selected, it is requested to the user to pick more than two points on the diagram, and NDCP will interpolate them using b-spline interpolation to create a the continuous curve. once the picking of the desired points is finished let press enter to show the dispersion curve on the FTAN diagram. If CLICK&HOLD option was selected, let click and hold the cursor on the FTAN envelope, then release it only at the end of the picking.in this case a linear interpolation is used to get the final curve.
4. if the user is not satisfied with the dispersion curve picked can repeat the process starting from the step 2
5. Let click on SAVE CURVE to keep the result on the workspace.
6. Let Click PREVIOUS or NEXT button to analyze the next or the previous data.

EXPORTING PICKED CURVES: Upon all curves are picked and saved, the button EXPORT ALL CURVES writes a 4-column ASCII file for each data analyzed in the working folder with the following information:

    name of the file: the same as of the input data (EXAMPLE.txt)

1st  col. 	Frequency [Hz]
2nd. col. 	Period [s]
3rd. col.	Velocity [km/s]
4th. col. 	Picked time [s]

Note: in case of two dispersion curves picked for the same crosscorrelation, two files will be written, one with the suffix 'a' for the picking done on the anticausal part and 'b' for the casual one (e.g. EXAMPLEa.txt and EXAMPLEb.txt)

To cite NDCP: Granados, I., Calo, M., and Ramos, V. (2019). NOISY DISPERSION CURVE PICKING (NDCP): a Matlab package for group velocity dispersion picking of seismic surface waves. Submitted to "Computer and Geosciences".

Comments and remarks can be sent to igranadosc@igeofisica.unam.mx