Attenuation of Lg in the western US using the USArray

• Published in: Geophysical research letters Vol. 35; no. 7; pp. L07307 - n/a
• Main Authors: Phillips, W. Scott, Stead, Richard J.
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 01-04-2008; Blackwell Publishing Ltd
• Subjects: attenuation; Continental crust; Earth sciences; Earth, ocean, space; Exact sciences and technology; Physical Properties of Rocks; Seismic instruments and networks; Seismic monitoring and test-ban treaty verification; Seismology; Tomography; Wave attenuation; Rocky Mountains; United States; Colorado; Sierra Nevada; Bitterroot Range; Columbia Plateau; U. S. Rocky Mountains; tomography; attenuation; Lg; models; inverse problem; density; North America; Variance; batholiths; crust; lateral variations; Q; amplitude; islands; shear zones; reduction
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2007GL032926

The unprecedented breadth and density of the USArray allows us to resolve lateral variations of 1‐Hz Lg attenuation to 0.5 degrees over much of the western United States. We collected over 31,000 Lg amplitudes from 547 events and 408 stations of the initial USArray footprint. Two‐dimensional tomographic inversion yielded Q ranging from 60 to 550, with a variance reduction of 47% relative to the best‐fit constant Q model (Q = 155). Q is low over most of the region, with lowest values associated with recent volcanic activity, and active shear zones. High Q is found in older, stable crust, notably the Colorado and Columbia plateaus, while smaller islands of high Q are associated with batholiths, including the Sierra Nevada, Peninsular, and Bitterroot Ranges, the western Mojave, and Okanogan Highlands, as well as other areas of competent crust such as the Harcuvar range, and two topographically bounded blocks in the Basin and Range.