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A High-resolution Phase Velocity Inversion for Crustal Structure of the Southeastern US Using Non-linear Signal Comparison

Determining the structural relationship between the Suwannee and its adjacent terranes on the margin of Laurentia is critical to understanding the formation of Laurentia and the tectonics of the Alleghenian orogeny. Previous studies demonstrated that the formation of the passive continental margin resulted from the movement of Laurentia towards the west-northwest during Proterozoic rifting. In our study there are two primary goals: 1) create high-resolution velocity maps to accurately quantify the extent of the terrane boundaries, 2) estimate the potential of the Non-linear Signal Comparison method in improving the phase velocity estimates using ambient noise data.

We use vertical-component ambient noise data from 100 broadband seismic stations (EarthScope FlexArray project called SESAME (Z9 2010-14; Parker, 2015)). Several approximately linear array subsets are used to obtain Green’s function. Then the phase velocities between two stations are estimated using Non-Linear Signal Comparison (NLSC; Zheng and Hu, 2017). This method mitigates the non-uniqueness problem at deeper depths. Phase velocities are estimated for Rayleigh waves at periods (15-45s) to obtain phase velocity dispersion curves. These dispersion curves are inverted to obtain 1D shear wave velocity profiles at locations along a transect; these profiles are then interpolated to produce 2D models.

NLSC improves the accuracy of Green’s functions, particularly at longer periods, by reducing the uncertainties of phase velocity estimates in dispersion curves at lower frequencies. Here, the time lag between two Green’s functions is not used directly. Instead, the exponent of the time lag is used and the normalized dispersion spectrum is calculated to estimate the dispersion curve. Dispersion curves are used to model the shear wave velocity using a Bayesian approach (Markov Chain Monte Carlo), which provides the maximum likelihood estimate of shear wave velocity. Results using real data show significant improvement in the estimation of Rayleigh wave phase velocity, particularly in the lower crust and uppermost mantle, compared to conventional techniques.

Session: Development, Enhancement and Validation of Seismic Velocity Models [Poster]

Type: Poster

Room: Evergreen Ballroom

Date: 4/21/2022

Presentation Time: 08:00 AM Pacific

Presenting Author: Debajeet Barman

Student Presenter: Yes

Additional Authors