Carter Lecture Series: Dr. Stephen Arrowsmith, "Both Sides of the Free Surface: Dense Infrasound Arrays Probe the Shallow Earth and the Lowest Atmosphere"

Dr. Stephen Arrowsmith, Professor of Earth Sciences at Southern Methodist University, presents "Both Sides of the Free Surface: Dense Infrasound Arrays Probe the Shallow Earth and the Lowest Atmosphere"

Abstract: Nodal seismometers transformed how seismologists sample the wavefield. The Sapphire, a nodal infrasound sensor developed at SMU, brings the same approach to the atmosphere above the ground. We use two dense deployments to probe both sides of the air-ground interface. On the SMU campus, a subwoofer swept 4 to 30 Hz for 24 hours into 48 sensors. treating the boundary layer as a vibroseis target, we invert travel time and amplitude independently for the near-surface sound speed gradient. Both place it 6 to 12 times steeper than a state-of-the-art reanaylsis and capture a nocturnal jet that ducts sound along one azimuth only. At NORFOX in Norway, 225 Sapphires, 60 SmartSolo nodes, and a DAS array recorded blasts 20 km awya. Infrasound couples compliantly into the ground, but DAS coupling exceeds the prediction form collacated nodes tenfold. In both cases, dense sampling reveals order-of-magnitude discrepancies that simple models cannot explain.

This seminar is part of the Dr. James Carter Lecture Series hosted by the Department of Sustainable Earth Systems Sciences.