Atmospheric Sciences Department to host infrasound seminar Tuesday The UND John D. Odegard School of Aerospace Sciences Department of Atmospheric Sciences will host Thomas Gabrielson, professor of acoustics at Penn State University, for a seminar titled “Natural Infrasound: Sources, Transmission Through the Atmosphere, and Detection.” The seminar will take place at 3 p.m. Tuesday, Sept. 22, in 210 Clifford Hall. The seminar is free and open to the public. Abstract: Some of the most interesting and provocative acoustical phenomena are associated with frequencies well below those of human perception. Severe storms, ocean waves, meteors, aurora, volcanoes, and earthquakes produce acoustic waves that can be detected thousands of miles away. The associated pressure oscillations may take between one tenth of a second and one hundred seconds per cycle. Furthermore, these pressure waves can be “trapped” in a persistent, low-loss acoustic “duct” that extends from the ground to an altitude of 100 km (62 miles). Gabrielson is currently doing field research in Manitoba, and, in addition to presenting the seminar, he will be visiting with various faculty at UND. Infrasound is sound that is lower in frequency than 20 cycles per second, the normal limit of human hearing. The study of such sound waves is sometimes referred to as infrasonics, covering sounds beneath 20 Hz down to 0.001 Hz. This frequency range is utilized for monitoring earthquakes, charting rock and petroleum formations below the earth, and in atmospheric sciences. -- Juan Pedraza, Writer/Editor, University Relations, juanpedraza@mail.und.edu, 777-6571