RUI: Geophysical Measurements Using Ring Lasers and Arrays

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In keeping with the goal of the "RUI: Geophysical Measurements Using Ring Lasers and Arrays" award to help create an infrastructure for advancing research in the Earth sciences, undergraduate students at Hendrix College in Conway, Arkansas are examining the rotational ground motion generated by earthquakes in the Central United States, atmospheric infrasound, and the characteristics of the Mississippi Embayment. In these studies, the students are utilizing measurements from large ring laser gyroscopes in conjunction with the seismographs and barometric pressure gauges that are part of the NSF Transportable EarthScope Array. Seismologists have known for years that earthquakes generate rotational ground motion in addition to vertical and lateral ground movement; the potential hazards from the rotational components of earthquakes are not completely understood. Two approaches for measuring the rotational components of seismic waves are through the use of large ring laser gyroscopes and arrays of seismographs. In addition to being sensitive to seismic waves, large ring laser gyroscopes have proven to be sensitive to atmospheric infrasound. Measurements from the ring laser gyroscopes and the barometric pressure readings from the NSF Transportable EarthScope Array are in use by the students to study the infrasound signatures from phenomenon as varied as hurricanes, volcanoes, Chinook winds over the Rocky Mountains, and microbaroms from ocean standing waves. As an example, infrasound signatures from hurricanes can provide information about their internal structure and perhaps provide information about their intensity variations. During 1811-1812, three large earthquakes in the Mississippi Embayment shook the Central United States with epicenters close to the small town of New Madrid, Mo. Estimates of the earthquake magnitudes range from slightly above seven to nearly eight. If earthquakes of this magnitude were to reoccur, there could be catastrophic damage to metropolitan areas such as Memphis, TN. In an attempt to better understand the danger from the New Madrid fault, NSF has funded the deployment of a dense seismic array that will supplement the NSF Transportable EarthScope Array. Hendrix College students are using the results from the dense array in their rotation ground motion studies and are gaining hands-on seismological field experience in helping to deploy seismographs in the dense array.