Electronic Supplement to
Aftershock Detection Thresholds as a Function of Time: Results
From the ANZA Seismic Network Following the 31 October 2001 Anza, California,
ML 5.1 Earthquake
by D. Kilb, V.G. Martynov, and F. L. Vernon
QuickTime Movies: Juxtaposition of Seismograms to Assess Aftershock Viability
Within the Mainshock Coda
Goal: When a large earthquake (mainshock) occurs, the following smaller earthquakes (aftershocks) are often obscured by the large decaying amplitude of the mainshock's seismic waves (coda). This makes it difficult to identify early aftershocks. Here, we use visualization techniques to quantify when early aftershocks are identifiable within the mainshock coda.
Method: We linearly add seismograms from a magnitude 3.2 earthquake to the continuous waveform data of the 2001 sequence. We start with an enforced 60 second time shift between the two earthquakes. For this large time large the magnitude 3.2 earthquake is easily identified in both the time domain and the spectragram for all stations within 70 km of the mainshock. We interactively reduce the lag time between the two events by 1 second and assess when the magnitude 3.2 earthquake is no longer visible within the mainshock coda. A Hanning window taper is initially applied to the waveform data, and the spectrograms are computed using 2.0 second windows with an overlap of 0.01 seconds. Conversion from the time-domain to the frequency domain is performed using a multitaper method (Thomson, 1982; Vernon, 1989) using the MATLAB routine PMTM with the time-bandwidth product set to 4.
View/Download Quicktime Movie Files:
| Movie | Action | File Name | File Size |
|---|---|---|---|
| Component HHZ | View in browser | Kilb_HHZ.mov | ~34 MB |
| Download | Kilb_HHZ.mov.zip | ~27 MB | |
| Component HHE | View in browser | Kilb_HHE.mov | ~26 MB |
| Download | Kilb_HHZ.mov.zip | ~21 MB | |
| Component HHN | View in browser | Kilb_HHN.mov | ~29 MB |
| Download | Kilb_HHN.mov.zip | ~23 MB |
Tech Note: The three movie files linked above may require Apple's free Quicktime software to view. Quicktime is included on all Apple Macintosh and many Microsoft Windows computers. If you need to install Quicktime software it can be downloaded from http://www.apple.com/quicktime/. Users of Linux or Unix operating systems may be able to play these movies using open source software such as Mplayer, Totem, or VLC.
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