Crustal Structure and Stress Regime of the Appalachian Basin and Surrounding Areas
Open Access
- Author:
- Homman, Kyle A
- Graduate Program:
- Geosciences (PHD)
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 12, 2023
- Committee Members:
- Andrew Nyblade, Chair & Dissertation Advisor
Charles Ammon, Major Field Member
Derek Elsworth, Outside Unit & Field Member
Sridhar Anandakrishnan, Major Field Member
Donald Fisher, Program Head/Chair - Keywords:
- Crustal Structure
Receiver Functions
Seismology
Geophysics
Precambrian Structure
Appalachian Basin - Abstract:
- In this thesis, I present new models for the crustal structure and stress regime across the Appalachian Basin in eastern North America to answer outstanding questions about the nature and origin of the tectonic framework in the area. In Chapter 2, a Precambrian basement model for the Pennsylvania portion of the Appalachian Basin is developed using newly available broadband and reflection seismic data combined with previously published point estimates for basement depth in the region. Basement depths across the region are generally consistent with the structure expected from a plate flexure model, with a gradual thickening of the basement from ~1,500 m in the northwest to ~6,000m in the southeast. However, two regions, the Rome Trough and Scranton Rift, have basement depths over deepened by a few kms. The cause of the over deepening in these regions can be attributed to the failed rifting associated with the breakup of the Rodinia supercontinent. In Chapter 3, a crustal structure model for the Appalachian Basin and surrounding areas is constructed using newly available broadband seismic data and a joint inversion of P-wave receiver functions and surface wave dispersion measurements from previous studies. Crustal thickness across the area averages ~44 km and varies between tectonic domains, with the thinnest crust occurring in the Coastal Plain and Carolina domains (34 km) and the thickest crust occurring in the Elzevir block and Cratonic areas (46 km). Anomalously thick crust in several areas is imaged, including along the Grenville Front and in northwestern Pennsylvania. Thinner than average crust is found beneath the Rome Trough and Scranton Rift, consistent with positive Bouguer gravity anomalies associated with these structures. In Chapter 4, new earthquake focal mechanisms obtained by double-couple inversion for 30 earthquakes that occurred between 2013 and 2023 within and surrounding the Appalachian Basin are combined with other published stress indicators to investigate the stress regime across the mid-Atlantic region of eastern North America. The new focal mechanisms constrain an east- west transition in the stress regime within a narrow geographic region trending N-S through central Pennsylvania and nearly coincident with the Allegheny Front. Reverse faulting is found to the east of this region and strike-slip faulting to the west. The favored explanation for the change in the stress regime is the deflection in tractions at the base of the lithosphere associated with sublithospheric mantle flow is it impinges on the eastern edge of thick cratonic North American lithosphere beneath central Pennsylvania.