Infrasonic and Gravity Wave Studies in the Central United States

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Infrasonic and Gravity Wave Studies in the Central United StatesSeismometers of the Transportable Array (TA) not only directly measure ground motion due to sources within the Earth's solid interior, they also indirectly provide valuable information about other phenomena that affect ground motion, such as atmospheric infrasound and gravity waves. Recently all 400 sites of the TA were retrofitted with barometers and infrasonic microphones. The Earthscope Science Plan includes as a scientific target the "cryosphere, hydrosphere, and atmosphere". Specifically, "studies of the infrasonic field allow for novel deep sounding of atmospheric structure and facilitate quantitative characterization of volcanic, oceanic, and other infrasonic sources." It has been recently shown that the density of TA sites permits one to accurately locate infrasonic sources, regardless if the infrasonic signals are registered by seismometers or microphones. This project is expanding upon previous Earthscope-funded work on the detection and location of more than 900 infrasonic pressure disturbances, or "skyquakes", that were registered by the seismic USArray during 2007-08 in the western U.S. Specifically, methods are being improved and applied to the seismo-acoustic USArray in the central U.S. Previously undetected skyquakes are being identified as are sources of gravity waves that propagate across the TA. The goals of this project are to identify the occurrence, waveform structure, and propagation statistics of these sources from 01/2009 through 03/2012. Correlations are being made between these events and atmospheric phenomena such as tornadoes and gust fronts. This work is resulting in two new databases of infrasonic and gravity wave event locations, arrival characteristics, and waveforms. The project is also illuminating infrasonic arrival branches in fine detail from several high-quality events.