GMV, the USArray Ground Motion Visualization
View GMVs: www.iris.edu/spud/gmv
Create customized GMVs: see details below
The Transportable Array component of the USArray/EarthScope project is a rolling array of 400 broadband stations deployed on a uniform 70-km grid (see map to the right). 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.
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 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. The following table summarizes the parameters used to generate GMVs.
Create Customized GMVs
To create customized GMVs, with parameters other than those used by the automated system, download the MATLAB script below 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.
— Chuck Ammon, Professor of Geosciences at Penn State’s original concept and visualizations. Read more
— Bob Woodward at IRIS - adapted the visualization code to MATLAB