Data Services Products: GMV The Ground Motion Visualization

Summary

Visualizations of real data showing how seismic waves sweep across the North American network of seismic stations for which data are collected and served in real time at the IRIS DMC. Watch how seismic waves from earthquakes in the US and around the world cause the ground to move at each seismometer location.

Description

North American network of seismic stations
North American network of seismic stations (red circles, as of December 6, 2017)
with LH? components. Data from these stations are collected and served in
real time at the IRIS DMC and are used to produce GMVs.

Starting on December 6, 2017, the Ground Motion Visualization (GMV) videos are created using data from the North American network of seismic stations that are arriving to the IRIS DMC in realtime (virtual network _REALTIME). Prior to this change, GMVs were generated using data from the Transportable Array (TA) component of the USArray/EarthScope project.

The Ground Motion Visualization (GMV) is a video-based IRIS DS 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 most 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.

PARAMETER vertical-component 3-component
Network _REALTIME1 _REALTIME1
Channel LHZ LHZ, LHN, LHE
Event magnitude US: ≥5.5; world: ≥6 world: ≥ 7
Taper 5% 5%
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-100s2 M≥6.5 500s-100s2
Travel-time estimation IASP91 IASP91
Rayleigh slowness 28.5 s/degree 28.5 s/degree

1 on 2017-12-06 the network was changed from US-ALL to _REALTIME

2 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, http://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.

Citations and DOIs

To cite the IRIS DMC Data Products effort:

  • 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 Applications, Seismological Research Letters, 83(5), 846–854, https://doi.org/10.1785/0220120032.

To cite the IRIS DMC GMV data product or reference use of its repository:

To cite the source or reference the use of a particular GMV:
    – select the GMV of interest
    – click on Citations to obtain its DOI
    – insert the DOI in below reference:

  • IRIS DMC (2010), Data Services Products: GMV The Ground Motion Visualization, doi:INSERT DOI HERE.

Credits

  • Chuck Ammon, Professor of Geosciences at Penn State’s original concept and visualizations.
  • Bob Woodward at IRIS – adapted the visualization code to MATLAB
  • Manochehr Bahavar, IRIS DMC

Timeline

2010-02-25
GMV online, automated production of GMV started
2010-10-20
3-component GMVs online
2011-03-24
Customized GMV online
2013-10-22
Super GMVs online
2015-10-05
Expanded to include Alaska

Categories

Tags

GMV