Mapping the Sources of Proximal Earthquake Infrasound

We recorded a M _WR 3.6 earthquake in Idaho (USA) on 7 April 2020 with a network of six three-element infrasound arrays and co-located broadband seismometers situated within 25 km of the hypocenter. Infrasound array processing is used to identify the arrival of seismic-to-atmospheric coupled phases and as much as 90 s of infrasound coda. Apparent velocities ranging from seismic speeds to subhorizontal atmospheric sound speeds are attributed to a superposition of coincident waves arriving at the arrays. We find that the arriving infrasound originates from a broad range of back azimuths that deviates from epicentral back azimuth and indicates the ubiquity of secondary radiators for this relatively small earthquake. Secondary radiators, which often locate in regions of elevated topography, are identified using backprojections and earthquake initiation time. Analysis of infrasound sources from proximal earthquakes can be used to map ground shaking distributions, which are important for assessment of earthquake hazards.