An Experimental Ultrasonic Method to Determine A Scattering Quality Factor, with Application to Earth’s Inner Core

Inner core seismic attenuation is anomalously large, which can be attributed to

• high anelasticity (intrinsic attenuation), and/or
• scattering from reflections off differently oriented crystals. The former is a material property of the inner core iron alloy, but the latter is due to the microstructure (shape, size, texture) of inner core Fe crystals, as well as the single crystal Fe elastic anisotropy. Understanding inner core scattering attenuation will help infer inner core microstructure and hence evolution.

We conducted ultrasonic experiments on hexagonal close-packed zinc-tin alloys, as an analog for the inner core hcp Fe alloy. The goal is not to study intrinsic attenuation, but simply to compare scattering attenuation for different microstructures that are likely relevant to the inner core. To study scattering attenuation, we argue that the microstructure is more important than the precise alloy material. We defined and measured a scattering quality factor \(Q_z\), and show how to scale the laboratory results to estimate \(Q_{zIC}\) in the inner core.

Recommended citation: Ming Gong, Michael I. Bergman, An experimental ultrasonic method to determine a scattering quality factor, with application to earth's inner core, Physics of the Earth and Planetary Interiors, 2025, 107456, ISSN 0031-9201, https://doi.org/10.1016/j.pepi.2025.107456.
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