27.1 Codaq

The program will calculate coda Q (hereafter called Q) for a series of events and stations at given frequencies. On completion, the average values are calculated and a Q vs f curve is fitted to the calculated values. The program will also plot the individual events and filtered coda windows.

The principle for calculation is the standard coda Q method, whereby a coda window is bandpass filtered, an envelope fitted and the coda Q at the corresponding frequency calculated. The envelope is calculated RMS value of the filtered signal using a 5 cycle window. The program used here is the one described in Havskov et al. (1989) and in more details in Havskov et al. (2016). The program can only operate in connection with the SEISAN format S-files. The program can use all waveform file types accepted by SEISAN and there can be more than one waveform file in the S-file. The program will also take advantage of the SEISAN database structure.

NOTE From SEISAN version 10.6, the error calculations in CODAQ has changed. Luis Matias pointed out that they seemed too small and indicated how to do it correctly (see https://en.wikipedia.org/wiki/Propagation_of_uncertainty). Consequently, most errros have incrased and this also affected the calcualted of Qzero and Qalpha (see later for definition). So rerunning CODAQ with identical data might give differenr results from verison 10.6 as comparesd to earlier versions.