Table 1
The attributes included in the three bundles of attribute functions in the seismic attributes library. The first column is the attribute number used by Provost et al. [19], the second column provides a description of the attribute, and the final column lists the attribute category, and thus attribute function bundle.
| NUMBER | DESCRIPTION | BUNDLE |
|---|---|---|
| 1 | Duration | Waveform |
| 2 | Ratio of the mean over the maximum of the envelope signal | |
| 3 | Ratio of the median over the maximum of the envelope signal | |
| 4 | Ratio between ascending and descending time | |
| 5 | Kurtosis of the raw signal (peakness of the signal) | |
| 6 | Kurtosis of the envelope | |
| 7 | Skewness of the raw signal | |
| 8 | Skewness of the envelope | |
| 10 | Energy in the first third of the autocorrelation function | |
| 11 | Energy in the remaining part of the autocorrelation function | |
| 12 | Ratio of 11 and 10 | |
| 13–17 | Energy of the signal filtered in 5–10 Hz, 10–50 Hz, 5–70 Hz, 50–100 Hz, and 5–100 Hz | |
| 18–22 | Kurtosis of the signal in 5–10 Hz, 10–50 Hz, 5–70 Hz, 50–100 Hz, and 5–100 Hz frequency range | |
| 24 | Mean of the discrete Fourier transform (DFT) | Spectral |
| 25 | Maximum of the DFT | |
| 26 | Frequency at the maximum | |
| 27 | Central frequency of the 1st quartile | |
| 28 | Central frequency of the 2nd quartile | |
| 29 | Median of the normalized DFT | |
| 30 | Variance of the normalized DFT | |
| 34–37 | Energy in DFT for | |
| 38 | ‘Spectral centroid’ (as defined by Provost et al.) | |
| 39 | Gyration radius | |
| 40 | Spectral centroid width | |
| 68 | Rectilinearity | Polarity |
| 69 | Azimuth | |
| 70 | Dip | |
| 71 | Planarity |
Figure 1
Top: Diagrammatic representation of algorithm used to identify events from a single seismometer comprising one or more channels (traces show their Euclidean norm). The characteristic function for an STA/LTA algorithm is used to ‘trigger’ events (shown in red) and small gaps between these events (shorter than thr_event_join) are ignored (orange). No events are present at other times (shown in green). Bottom: Representation of algorithm used to identify events in the ‘reference event’ and ‘trace’ catalogues for seismic arrays (with multiple seismometers). The example shows an indicative array with N = 3 seismometers and thr_coincidence_sum = 2 simultaneous detections. Events identified for the single seismometers traces are shown in red (as given in the top panel). The duration of these events is extended at each end by half the delay in arrival time of a wave between the most distant seismometers in the array (shown in deep red). The reference event is identified as the times when thr_coincidence_sum = 2 seismometers have a detection (shown in red or deep red); small gaps with fewer seismometers are joined over (shown in orange). The events at each seismometer are simply the events identified from the single seismometer traces (red but not deep red), but with any times between events that occur during the reference event also included (shown in grey).
Figure 2
Waveforms of an event detected using four seismometers (BB01, BB03, BB04 and BB06) comprising part of a seismic array on the Whillans Ice Stream in Antarctica from 13:35:37 on 16 December 2010. The top, middle and bottom panels show the vertical, north and east component of the signal respectively. The waveforms for each seismometer start 30 seconds prior to the start time in the trace catalogue and terminate 60 seconds after the stop time. The code to reproduce this plot is provided as a worked example.
Figure 3
Corner (or pair) plot illustrating the correlation between spectral attributes for the events detected at Ilulissat, Greenland on 1 January 2018 using the recursive STA/LTA algorithm. The attribute names are defined to match those used by Provost et al. [19]; see Table 1 for a description of each attribute. In this example, attribute 26 considers a frequency range close to the sampling rate of the recorded signal, therefore, it has null value for all events. The code to reproduce this plot is provided as a worked example in the detailed documentation provided with the software.