Fig. 6: Maps of inferred secondary infrasound sources. Because seismic waves propagate at a range of speeds, backprojections are less certain in range than in backazimuth; these maps err on the side of inclusion and therefore contain some points that do not radiate infrasound.
From: Remotely imaging seismic ground shaking via large-N infrasound beamforming
a Central Idaho topographic map showing secondary infrasound identified in Fig. 4c for the local Stanley earthquake. The earthquake epicenter coincides with the PARK station so they are plotted as the same point. Secondary infrasound observed at PARK originates only out to nearby mountain crests, mainly to the southwest, west, and northwest. b Map of the western US showing secondary infrasound in the regional earthquake identified in Fig. 5d between 1000–2500 s after the earthquake (limits for these arrival times shown in dashed lines); local secondary infrasound (150–500 s) is excluded because of the very high uncertainty in seismic travel times. Secondary infrasound observed at PARK originates mostly from the southwest, south, and southeast, and the source region follows some mountain ranges. Amplitudes of select seismic stations are indicated by radii of black dots. c Select vertical seismograms from stations in (b), with dashed lines indicating average maximum/minimum seismic wave speeds.
