Enhanced imaging of deep lithospheric and shallow near surface structures through innovations in seismic interferometry and array processing.

This dissertation presents four studies that develop and apply passive seismic imaging methods to investigate Earth structure across a range of scales, from the shallow near-surface to the deep upper mantle. The first study uses array analysis of ambient noise autocorrelograms recorded by a dense nodal array near Sweetwater, Texas to image P-wave reflectivity of the upper mantle. A coherent reflection event at approximately 26 seconds two-way time is detected consistently across eighteen linear sub-arrays and is interpreted as a PpP-type reflection response from a sharp, negative velocity gradient at the Lithosphere-Asthenosphere Boundary (LAB) at approximately 90 km depth. The detection of this event in a relatively high-frequency band, combined with its positive polarity in autocorrelograms, indicates a steep velocity gradient at the LAB consistent with partial melt or volatile enrichment in the asthenosphere. The second study applies teleseismic P-wave coda autocorrelogram imaging to broadband stations across 4 seismic networks in northeastern North America to investigate upper mantle discontinuities. A positive-polarity reflection event is detected between 83 and 120 km depth at all stations and is interpreted as marking the LAB. Combined application of velocity analysis and the Parabolic Radon Transform techniques to autocorrelogram event gathers, facilitates the identification of reflection responses from upper mantle discontinuities. The LAB is identified as a steep, negative gradient that appears with a positive-polarity in higher-frequency autocorrelograms. The third study develops a novel array covariance matrix-based method for extracting Rayleigh wave phase velocity dispersion curves from large-N nodal arrays in the presence of non-stationary local noise sources. The method is applied to sub-arrays of the Sweetwater dense array to retrieve high-resolution pseudo-3D shear-wave velocity models of the shallow subsurface. The fourth study extends the array covariance matrix approach to transient and opportunistic sources including train-induced vibrations and urban traffic noise recorded by nodal arrays and distributed acoustic sensing (DAS) fiber-optic cables. Application to the Tierra Grande nodal deployment and a dark fiber cable at the University of Louisiana at Lafayette demonstrates that these anthropogenic sources can serve as reliable, passive sources for shallow near-surface shear-wave velocity imaging, enabling cost-effective monitoring of urban subsurface structure.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Doctoral

Grantor

Baylor University.

Year dc:date.issued

2026

Author dc:creator

• Soni, Yashwant, 1994-

Advisor dc:contributor.advisor

• Pulliam, Jay.

• Seismic interferometry.
• Autocorrelograms.
• Ambient noise.
• Surface waves.
• Array covariance matrix.
• Lithosphere asthenosphere boundary.
• Body waves.
• Seismic imaging.
• Array processing.

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/2104/15034

OAI identifier oai:identifier

oai:baylor-ir.tdl.org:2104/15034