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Investigating the Intrinsic Attenuation of Large Low Velocity Provinces

Description: 

At the base of the mantle, two massive anomalously seismically slow regions (LLVPs) have been discovered; their nature, origin, and role in global mantle dynamics are still debated. Seismic waves exhibit a notable velocity drop when traversing these structures, previously explained by elevated temperature and iron enrichment. However, inferences of temperature and composition from velocity constraints are inherently nonunique. The attenuation experienced by seismic waves as they travel through LLVPs can provide additional information on their temperature, because attenuation is expected to have an exponential dependence on temperature. While the elevated temperatures expected for LLVPs would imply higher attenuation, estimates of attenuation of the LLVPs remains debated. Indeed, recent studies based on normal modes argue that attenuation is lower in LLSVPs than in the surrounding mantle (Talavera-Soza et al., unpublished), suggesting that grain size, rather than temperature, perhaps plays a dominant role in controlling attenuation variations in the lower mantle. Here, we analyze previously published databases of body wave attenuation measurements (Lai and Garnero, 2019, 2020), specifically t* of S, SS, ScS and other phases sensitive to the lowermost mantle structure. We account for the effects of upper mantle attenuation variations using differential t* of reference phases and corrections based on published attenuation models in order to constrain the attenuation in LLVPs. LLVP areas appear to be characterized by multimodal differential t* values that have a higher attenuation on average compared to regions outside the LLVPs. We discuss our results in the context of previously published models of lower mantle attenuation.

Session: Earth’s Structure from the Crust to the Core - IV

Type: Oral

Date: 4/16/2025

Presentation Time: 05:30 PM (local time)

Presenting Author: Donovan

Student Presenter: Yes

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