AN ANIMATED MAP OF TEXAS AND OKLAHOMA SEISMICITY FROM 1973 TO THE PRESENT

It is now well documented that the rate of earthquake occurrence in the central and eastern United States has increased dramatically since about 2008. Ellsworth, in a 2013 Science paper, attributes this increase to induced seismicity associated with waste water injection in unconventional hydrocarbon resource plays. He produced a simple but alarming figure of cumulative event counts for magnitudes greater than or equal to 3 over 1967 to 2012.

If a more restricted geographical region is selected (30N to 35N and 94W to 100W), the Ellsworth plot can be reproduced. This region encompasses eastern Texas and southern Oklahoma which includes major fault zones related to Paleozoic and Mesozoic tectonic activity. Can this trend be captured and effectively displayed in the form of an animated map? Can the animated map bring to light the relationship of the seismicity trends to known geological features?

The map is presented in the form of a movie complete with sound track. The earthquake events are taken from the Advanced National Seismic System (ANSS) catalog, a recent effort to integrate the results from diverse local and national seismic network catalogs. Each frame of the movie displays events in a week-long time interval with symbols linearly scaled by magnitude (log scale). Further time dependence of the seismicity is provided by a linear fading of the symbols over a recurrence interval based on the Gutenberg-Richter relationship fit to the local catalog prior to 2008.

The sound track is provided by the vertical component record of the Venus, TX earthquake of 5/7/2015 recorded at station WHTX. The seismogram is converted to a 1.5 s long audible sound by a 200 Hz frequency shift. The amplitude is scaled for each event by the square root of the seismic moment.

Geographical reference is provided by state boundaries and the Interstate Highway System. Mapped surface and subsurface faults are also plotted on the base map. The movie is intended to be informative for the general public, so the base has been kept relatively straightforward. It is possible to produce more specialized base maps for geoscientific audiences.

Exposure of the map to a number of audiences has been found to produce a dramatic effect while also conveying significant scientific information.