Here was the link they included for the source data ...
http://aslwww.cr.usgs.gov/Seismic_Data/telemetry_data/map_sta_eq.shtml
poles are reversing?
Looks like there’s a concentration around the Gulf of Mexico - are there more stations there for a reason?
http://aslwww.cr.usgs.gov/Seismic_Data/telemetry_data/map_sta_eq.shtml