Fig. 4: Seismicity and thorium concentration.

A Map of the western US showing the location of East River (ER) and Coal Creek (CC) in Colorado, seismic monitoring stations and the epicenter of seismic event #9363207. Map adapted from Google Earth. B Example of seismicity preceding thorium excursions in ER and CC that was recorded at two stations in Colorado and attributed to catalogued event #9363207.