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Site Amplification and Crustal Attenuation in the CEUS: Joint Tomographic Models for Ground Motion Analysis

Description: 

The amplification of earthquake shaking by local geologic structures presents significant seismic hazards, particularly in sediment-rich regions like the Gulf and Atlantic Coastal Plains and Illinois Basin of the central and eastern United States (CEUS). This study employs tomographic joint inversions to separate the overlapping and frequency-dependent contributions of crustal attenuation (1/Q), source characteristics, and site amplification in the CEUS. Using Lg wave amplitudes recorded over long raypaths (~200–1500+ km), we image crustal Q in seismically quiet yet densely populated areas such as the Coastal Plains while simultaneously accounting for sedimentary basin and coastal plain amplification effects. Seismic data from over 1400 events (Mw > 3.5) recorded by the EarthScope Transportable Array (TA), the newly deployed N4 network, and other broadband stations enable robust analyses of both vertical and horizontal Lg wave amplitudes, producing the first comprehensive CEUS attenuation maps since the TA’s deployment.

Preliminary results reveal significant spatial variations in crustal Q across the CEUS. Attenuation is highest in Yellowstone, the Basin and Range, Southern Rockies, and Oklahoma Aulacogen; intermediate in the Gulf and Atlantic Coastal Plains, Midcontinent and St. Lawrence Rifts, and intraplate uplifts (e.g., Black Hills, Adirondacks); and low in the Colorado Plateau, Wyoming Craton, and broadly across the Great Plains to the Grenville Front. By contrast, mountainous areas of the western U.S. have the lowest site amplifications, cratonic basins the highest, and coastal plains appear intermediate. These maps will support the development of improved nonergodic ground motion models by incorporating frequency-dependent site amplification terms for vertical and horizontal motions. This project will quantify seismic attenuation, validate coastal plain amplification models, and assess sedimentary effects, delivering attenuation maps across eight frequency bands (~10–0.1 s) and frequency-dependent amplification factors critical for seismic hazard assessment.

Session: Station Installations and Site Conditions, a Quest for Improved Strong Motion Database - II

Type: Oral

Date: 4/16/2025

Presentation Time: 05:30 PM (local time)

Presenting Author: Anuradha

Student Presenter: No

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