Visualizations of real data showing how seismic waves sweep across the USArray network of seismic stations. Watch how seismic waves from earthquakes in the US and around the world cause the ground to move at each seismometer.
The Transportable Array (TA) component of the USArray/EarthScope project is a rolling array of 400 broadband stations deployed on a uniform 70-km grid (map ). Ground motion data recorded by this very large aperture array, along with those recorded by other stations from USArray, are used for visualization of seismic waves as they cross the contiguous United States.
The USArray Ground Motion Visualization (GMV) is a video-based IRIS DMS product that illustrates how seismic waves travel away from an earthquake location by depicting the normalized recorded wave amplitudes at each seismometer location using colored symbols (see maps below). The color of each symbol depicts the amplitude of the vertical ground motion, as detected by the station’s seismometer
(for TA stations this represents velocity of ground movement) and normalized to its peak amplitude. The color changes as waves of differing amplitude travel past the seismometer. Blue indicates downward ground motion while red represents upward ground motion with the darker colors indicating larger amplitudes.
In addition to normalization, each trace is also magnified by a constant magnification factor. Such a trace magnification highlights weaker arrivals at the expense of saturating colors of the stronger arrivals. GMV’s default magnification is 10 and it is suitable for most events. However, for the events located between 10°- 20° from the “center” of the array, the magnification is dropped to 5 and for the events located less than 10 degrees from the “center” of the array, no magnification is performed. This change in magnification prevents extreme highlighting of the unwanted near-source arrivals.
Under favorable conditions,when multiple events from the same source area occur within 1 to 1.5 years of each other, it is possible to combine the associated GMVs to create a Super (Combined) GMV that provides extensive coverage for the United States (see map to the right).
For large events, magnitude ≥ 7, in addition to the vertical-component GMV (map below, left), a 3-component GMV (map below, right) is also produced that uses “tailed” symbols with the direction and length of their tail representing the direction and amplitude of the normalized horizontal ground motion at the corresponding location respectively.
To compliment the wave motion depicted by the symbols on the map and to provide a sense for the ground displacement, the visualizations also include representative displacement seismogram(s), obtained from the velocity seismograms, for a reference station that is marked by a yellow circle on the map. The horizontal axis represents the time after the event and a vertical blue bar at the end of the trace shows the maximum detected ground displacement. The vertical-component GMVs show the vertical seismograms (Z) and the 3-component GMVs additionally include the horizontal seismograms (N-S and E-W). For the 3-component GMVs the horizontal traces are normalized together but independent of the vertical component.
Table: A summary of parameters used to generate GMVs.
|Channel||LHZ||LHZ, LHN, LHE|
|Event magnitude||US: ≥5.5; world: ≥6||world: ≥ 7|
|Filter type||Butterworth degree 4||Butterworth degree 4|
|Filter band||50s-20s 6.0>M≥5.5 / 250s-50s 6.5>M≥6.0 / 500s-100s1 M≥6.5||500s-100s1|
|Rayleigh slowness||28.5 s/degree||28.5 s/degree|
1 On 2012-01-25 the filter band was changed from 1000s-100s to 500s-100s in order to remove the low frequencies seen for some events
Create Customized GMVs
To create customized GMVs, with parameters other than those used by the automated system, download (~24 MB) the MATLAB script (README, trest movie, ~19.3MB) or use the Customized GMV User Interface. This interface is also useful to produce GMVs for events and/or networks that are not usually processed by the automated system. For more information on this interface visit the How to Customize GMVs page.
Trabant, C., A. R. Hutko, M. Bahavar, R. Karstens, T. Ahern and R. Aster (2012), Data products at the IRIS DMC: stepping-stones for research and other application, Seismological Research Letters, 83(6), 846:854. doi: 10.1785/0220120032
- Chuck Ammon, Professor of Geosciences at Penn State’s original concept and visualizations.
- Bob Woodward at IRIS – adapted the visualization code to MATLAB
There is no DOI currently assigned for this product.