MASA - Moscow Acoustic/Seismic Array


Overview: The Moscow Acoustic/Seismic Array is located near the small town of Moscow, TN, 30 miles east of Memphis. It is an experimental infrasound and three-component seismic array designed to record atmospheric acoustic shock waves (thunder from lightning during thunderstorms) in the band from 2-30 Hz. The scientific goal is to understand the coupling of low frequency acoustic waves with the seismic structure of the near surface. A previous study of a bolide sonic boom recorded by the CERI network (Langston, 2004) showed that infrasonic acoustic waves couple very efficiently with the ground and display a variety of leaky mode wave propagation effects that can be utilized to study the seismic structure of the upper 20m or so of the earth. Atmospheric acoustic sources can therefore be used to investigate site properties important for earthquake strong ground motion hazards assessments. The array was installed in late August 2005 and is currently (September 2006) still operating.

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Funding: The array was funded through discretionary overhead return funds by the University of Memphis and CERI.

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Graduate Students: Ting-Li Lin is a CERI Ph.D. student working on data from this array. The title of his thesis proposal is "Ground Motions Induced by Thunder".

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Array Location: The array is located at 35.09039 deg N, 89.43736 deg W on rural land northwest of the small town of Moscow, TN.

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Array Design: The array consists of 5 surface sites and a 10m deep borehole (see figure above). The spacing of the sensors was determined by assuming 5 Hz acoustic signals. 5 Hz is the expected site resonance. Each surface element contains an experimental infrasound instrument based on a Southern Methodist University design and an L28 three component geophone. A three-component L28 borehole instrument is emplaced at the bottom of the borehole. Each surface geophone is buried to a depth of about 25 cm. All seismic instruments were oriented with respect to north. An Earthworm data archiving system runs on a personal computer with a 16 bit, 24 channel digitizing card. Timing comes from a GPS receiver. There is extensive lightning protection for the electronics since the instruments are directly cabled to the central processing point about 200 m from the array.

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Infrasound Instruments: Here's what the infrasound instrument looks like:

Greg Steiner modified the SMU "Seattle Q1" design. The instrument was calibrated at the National Center for Physical Acoustics, Univeristy of Mississippi. Here is the frequency response relative to a B&K 4193 Microphone (that has a flat response).


Seismic Instruments: The L28 geophones were refurbished and calibrated before installation. Instrument polarity was checked using a local earthquake source to correlate waveforms between components and by a careful application of directed hammer blows to stakes ~1m from the instruments in all 4 compass directions.

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Acknowledgements: Greg Steiner, CERI Technical Director, designed the electronics for the infrasound microphone, an AM lightning detector, GPS and data input to the digitizer, and the physical cabinet and boards for the central receive facility. Steve Brewer, Digital Seismic Systems Supervisor, designed and configured the Earthworm system. Chris McGoldrick, Research Technician, and Greg Steiner drilled and cased the borehole and installed the array. Chris Powell was persuaded to give up a corner of the upper pasture for the array. All are gratefully acknowledged.

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