Seismic Background Noise Levels across the Continental United States from USArray Transportable Array: The Influence of Geology and Geography
Abstract
It has now been 17 years since McNamara and Buland (2004) characterized background noise levels across the contiguous U.S. using 61 broadband seismic stations and presented probability density functions of power spectral densities (PSDs). To improve seismic noise estimates across the U.S., we examine vertical component, seismic data from the EarthScope Transportable Array seismic network that rolled across the U.S. and southeastern Canada between 2004 and 2015 and form a large (10 TB) PSD database from 1678 stations that contains no smoothing or binning of the spectral estimates. Including station outages from TA, our database has a mean of 97.87% data completeness, and we present maps showing the spatial and temporal variability of seismic noise in 6 bands of interest between 0.2- and 75-s period. At 0.2 s period, seismic noise across the Eastern U.S. is predominantly anthropogenically generated and may be subsequently amplified more than 20 dB in the sandy and water-saturated sediments of the Southeastern U.S. Coastal Plains and Mississippi Embayment. 1 s noise shows similar amplification in these lithologies and is generated through a variety of mechanisms including cultural activity throughout Kentucky and the southeastern Appalachian Mountains, lake waves around the Great Lakes, and ocean waves throughout New England, the Pacific Northwest, and Florida. Both 0.2 and 1 s noise levels are the lowest in the mountain west portion of the U.S. We attribute this to a combination of installations on crystalline rock lithologies and reduced population density. Finally, we find that sensors emplaced in sandy, water-saturated lithologies observe median, diurnal variations in vertical component power at 18 to 75 s period, which we infer arise through local deformation driven by pressure variations. Ultimately, our results underscore that for shallow (< 5 m depth) sensor installation, bedrock provides superior broadband noise performance compared to unconsolidated lithologies.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.S54A..06A