Mapping the Sources of Proximal Earthquake Infrasound. Issue 23 (7th December 2020)

• Record Type: Journal Article
• Authors: Johnson, J. B.; Mikesell, T. D.; Anderson, J. F.; Liberty, L. M.
• Is Part Of: Geophysical research letters. Volume 47:Issue 23(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-07
• Subjects: array processing -- back azimuth -- backprojection -- earthquake infrasound -- seismo‐acoustics -- Stanley earthquake; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL091421
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We recorded a MWR 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. Plain Language Summary: Earthquakes are known to produce sounds, which encompass frequencies that are both perceptible and below the threshold of human hearing. Low frequency earthquake (infra)sound may be recorded with specialized microphones to understand how earthquakes shake Earth's surface. Our study uses six infrasonic microphone stations to detect and locate sound sources for a magnitude 3.6 earthquake that occurred within 25 km of the stations. The recorded infrasound is produced by ground shaking at both the infrasound stations and also over a wide distribution of areas coinciding with mountain topography. These secondary sources of earthquake sounds occur as seismic waves pass by and the resultant ground shaking perturbs the atmosphere. The identification of infrasound in this study is possible even though the earthquake size is relatively small. Key Points: A network of arrays is used to locate proximal infrasound sources for a M3.6 Idaho earthquake "Local infrasound" (at recording site) and "secondary infrasound" (from the epicentral region and from elevated topography) are identified Intermediate slowness values are common and are attributed to superposition of subhorizontal and subvertical propagating infrasound