27.1.4 General recommendations and example of test data

Coda window should be at least 30 seconds, minimum correlation coefficient larger than 0.6. For comparing coda values in different regions, ALL processing parameters must be identical including lapse time. In Havskov et al. (2016) the effect of the different parameters is investigated and a set of recomendations are given. The parmerters found in the example file in DAT are the parmeter used in Havskov et al. (2016). In DAT there is also an input file codaq.inp using available data in the test data base. The input file has been created with program SELECT (option 18, station code= CODAQ, distance range 0 to 100 km). The start of the file is

    1  /seismo/REA/TEST_/1990/12/13-1109-19L.S199012
SUE  SUE  SUE  ODD1 ODD1 ODD1 ASK  ASK  ASK
   Z    N    E    Z    N    E    Z    N    E
    2  /seismo/REA/TEST_/1995/08/22-0141-06L.S199508
OSG  OSG  OSG
   Z    N    E
    3  /seismo/REA/TEST_/1995/11/20-0401-59L.S199511
EGD  EGD  EGD  BER  BER  BER  ASK  ASK  ASK  ODD1 ODD1 ODD1 BLS5 BLS5 BLS5 KMY  KMY  KMY
   Z    N    E    Z    N    E    Z    N    E    Z    N    E    Z    N    E    Z    N    E
    4  /seismo/REA/TEST_/1996/06/07-1325-29L.S199606

which assumes that the test data base is installed under seismo. In a standard Windows installation, that would work. Under Linux it must be change to something like /home/seismo.... Alternatively create the file with SELECT.

Figure 27.1 gives an example of a codaq plot. There are no options for the codaq plots and the length of the window is always the first 200 secs from the original trace. If origin time or coda window is outside this 200-sec window and data is available, the program continues, but the coda window is not plotted on the figure.

Figure 27.1: An example of a coda Q plot. On top is shown the original trace and below the filtered coda windows. Note that 15 secs of noise are shown in front of the selected filtered coda window. The first 5 secs of the noise shown is used for calculating the S/N ratio. On each filtered plot is given F: Center frequency, Q: Q-value, zero means no Q-value could be calculated, S/N: Signal to noise ratio.