Shear Wave Velocity Model of the Southeastern United States From Ambient Noise Tomography With Double Beamforming

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

Determining the structural relationship between the Gondwanan Suwannee terrane (SWT) and adjacent terranes in the southeastern United States can help constrain the late Paleozoic accretionary formation history of Laurentia, the tectonics of the Alleghanian orogeny, and the nature of the breakup of Pangaea. Our modeling approach consists of two parts: 1) Compute Rayleigh wave group velocity maps using double beamforming to obtain the most accurate dispersion relations and 2) estimate a shear wave velocity model using “ant colony” inversion. We also compare the ant colony result to estimates produced with Markov Chain Monte Carlo inversion.

Vertical component seismograms are used from more than 400 stations of USArray, ANSS, and regional networks for the years 2010-present. Rayleigh wave group velocity dispersion curves are calculated between station pairs using double beamforming to admit only components of surface waves that propagate along great circle paths. Cross-correlations between vertical component of ambient noise data from subarrays are stacked between array centers as a function of velocity, azimuth, and time (i.e., a vespagram is produced) and frequency-time analysis is applied with phase-matched filters to create group velocity dispersion curves. Dispersion curves are used to obtain Rayleigh wave group velocity maps for the entire region and the maps are used to constrain locally 1D shear wave velocity models found via ant colony nonlinear optimization. Ant colony optimization is a computationally efficient and stable swarm intelligence method. The method has been shown to converge quickly to the global solution and to produce an accurate model.

Preliminary results with six months of data for a portion of the study region show significant differences between group velocity values and structural boundaries obtained with double beamforming and a conventional approach. Interpretations of the region’s tectonic history are therefore also affected.

Presenting Author: Debajeet Barman

Authors