Constraining Mantle Anelasticity Using S wave Amplitudes

Earthquakes generate seismic waves that propagate through the interior of the Earth, with their amplitude gradually decaying as they travel. This reduction in amplitude, known as attenuation or anelasticity, provides crucial insights into the properties of the materials they travel through. By analyzing mantle anelasticity, we can determine key characteristics of mantle materials, including their temperature, composition, and mechanical behavior.

These properties are essential for understanding the formation, evolution, and dynamics of the planet. This project aims to improve our understanding of mantle anelasticity by analyzing the amplitudes of seismic waves from a wide range of seismic phases. This research will establish an improved reference model for mantle anelasticity, which is important for understanding the material properties of the mantle and improving earthquake magnitude estimates.

In addition to advancing fundamental seismological research, this project will enhance geoscience education and outreach. The new dataset and corresponding Q model will be made publicly available, and the educational components will include undergraduate research opportunities, hands-on computer lab modules for geophysics students, as well as science communication through YouTube videos and exhibits at the Geosciences Museum.

In contrast to the well constrained 1-D seismic velocity structure, the 1-D attenuation structure of the mantle remains poorly understood. In this proposed work, we will use S-wave amplitudes to determine the radial attenuation structure of the mantle. The new amplitude dataset will include minor-arc S, SS, SSS, SSSS, ScS, Sdiff waves as well as major-arc SSS and SSSS waves and ScS multiples.

We will address major challenges in determining the radial structure of attenuation using body-wave amplitudes. In particular, the research activities will explore measures that can be used to assess geographic sampling to determine global average Q values, which will allow us to determine the number of independent observables and analyze the depth resolution of the radial attenuation model.

We will employ linear inversion and nonlinear forward modeling to obtain an optimal 1-D model using all available S wave measurements, including those affected by mantle triplications. We will investigate the frequency dependence of attenuation in the frequency range between 5 and 40 seconds. The new global Q model will provide an important reference for calculations of synthetic seismograms and expected energy loss due to wave propagation.

The improved model will enhance the resolution of the layered structure of mantle attenuation and help address key scientific questions related to asthenosphere thickness, transition zone rheology, and the thermal structure at the core-mantle boundary.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.