Seismic attenuation of the crust of the conterminous United States using Earthscope Transportable Array data
Abstract
Multiple tectonic episodes have lead the North American Continent to have distinct seismic characteristics that are segregated between the stable east and tectonically active western part. Past seismic studies have shown that lithospheric seismic velocities in the eastern United States are higher than seismic velocities of the western United States. Studies of heat flow data in the United States show that the lithosphere in the western United States is much warmer than the crust in the eastern United States. Heat flow, crustal thickness, and tectonic structure have been correlated to attenuation of seismic phases in the United States. Twenty earthquake events, spanning from Mw 3.9 - Mw 6 across the United States, have been used in this study to assess the seismic characteristics of the eastern and western United States. Data was collected using Earthscope's Transportable Array seismic network, which is a dense seismic network (70 km spacing), that initially started in the Western United States in 2004. Stations within this network are moved every two years eastward, until the network has been relocated to the east coast in 2014. Our investigation included over 50 seismic profiles, in order to understand how energy dissipates with distance in the eastern and western United States. Travel times were estimated for the Lg and Pg, Pn using vertical component data and Sn, Sg were estimated using horizontal seismic components. Attenuation was estimated for Lg for narrow band filtered data at f = 1 Hz, for Pg narrow band filtered data at f = 2 Hz. This study reveals an average Q values in the Eastern US of Lg and Pg are 163.4 and 276.81 and in the west 105.3 and 158.9, respectively. Frequency spectra of select signals revealed that, in general, high frequency seismic waves attenuate much faster as a function of distance, in the west than the east.
Degree
M.S.
Advisors
Braile, Purdue University.
Subject Area
Geophysics
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