High-Resolution 2D Lg and Pg Attenuation Models in the Basin and Range Region with Implications for Frequency-Dependent Q

Journal Article · Tue Oct 24 00:00:00 EDT 2017 · Bulletin of the Seismological Society of America

DOI:https://doi.org/10.1785/0120170172· OSTI ID:1438731

Pyle, Moira L. ^[1]; Walter, William R. ^[1]; Pasyanos, Michael E. ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Here, we develop high–resolution, laterally varying attenuation models for the regional crustal phases of Pg and Lg in the area surrounding the Basin and Range Province in the western United States. The models are part of the characterization effort for the Source Physics Experiment (SPE), a series of chemical explosions at the Nevada National Security Site designed to improve our understanding of explosion source phenomenology. To aid in SPE modeling efforts, we focus on improving our ability to accurately predict amplitudes in a set of narrow frequency bands ranging from 0.5 to 16.0 Hz. To explore constraints at higher frequencies where data become more sparse, we test the robustness of the empirically observed power–law relationship between quality factor Q and frequency (Q=Q₀f^γ). Our methodology uses a staged approach to consider attenuation, physics–based source terms, site terms, and geometrical spreading contributions to amplitude measurements. Tomographic inversion results indicate that the frequency dependence is a reasonable assumption as attenuation varies laterally for this region through all frequency bands considered. Our 2D Pg and Lg attenuation models correlate with underlying physiographic provinces, with the highest Q located in the Sierra Nevada Mountains and the Colorado plateau. Compared to a best–fitting 1D model for the region, the 2D model provides an 81% variance reduction overall for Lg residuals and a 75% reduction for Pg. These detailed attenuation maps at high frequencies will facilitate further study of local and regional distance P/S amplitude discriminants that are typically used to distinguish between earthquakes and underground explosions.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1438731
• Report Number(s): LLNL-JRNL--731686
• Journal Information: Bulletin of the Seismological Society of America, Journal Name: Bulletin of the Seismological Society of America Journal Issue: 6 Vol. 107; ISSN 0037-1106
• Publisher: Seismological Society of America
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES