Doctor of Philosophy
The EarthScope USArray provides an unprecedented improvement of ground motion recordings in terms of quality and spatial coverage across the central and eastern North America (CENA). This study investigates two attenuation problems in the CENA region i.e., developing ground motion prediction equations (GMPEs) for the Gulf Coast region and investigating seismic Lg wave attenuation in Oklahoma and its surrounding regions. Both problems utilize a common seismological advantage, i.e., the dense EarthScope USArray ground motion observations to improve our understanding of regional ground motion models and attenuation structure in CENA. I developed empirical GMPEs for the Gulf coast region based on the defined attenuation boundary locations and observed ground motions from raypaths entirely within the Gulf Coast region. The prediction equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5% damped pseudo-absolute acceleration spectra (PSA) at 21 periods between 0.1 sec to 10 sec. The dataset includes 10 within or near Gulf Coast earthquakes and 549 recordings for magnitudes ranging from M2.6 to M5.7 and epicentral distances from 20 to 1000 km. Additionally, the use of 2010 M7.1 Darfield, New Zealand observations provide some constraint at near distances and at large magnitudes for which Gulf Coast observations are not available. This study provides useful insight on how the observed ground motion amplitudes scale with the magnitude and distance dependent parameters through a functional model by incorporating source, path and site terms. Utilizing a data driven approach with defined Q regionalization, our GMPE model provides a new context to understand the variability in observed ground motions and relative usefulness of other GMPE models based on simulation or hybrid methods. In a subsequent study to investigate the regional attenuation in Oklahoma and surrounding regions, I applied a tomographic approach to explore the Lg wave attenuation in light of newer and denser data coverage by the recent induced and natural seismicity. The tomographic approach with sufficient crossing raypaths enables a better resolution of the lateral variation of Lg Q in a broad frequency range from 0.1 to 10 Hz. An average Lg quality factor, QLg, as a function of frequency for the study region is estimated as Q(f)=(629±153) f^((0.75±0.16) ) in the frequency range 1.0 Hz ~ 10.0 Hz. The tomographic results show that the southern part east of 96∘W in the Gulf coastal plain is characterized by lower-than-average QLg values, i.e., higher attenuation, while Northeast trending high QLg values (lower attenuation) are observed in the region covering central Oklahoma and parts of Texas. The tomographic setup extracting the source, path and site effects from seismic Lg amplitudes provides a methodological approach to understand and quantify the ground motion parameters and their trade-off.
Dissertation or thesis originally submitted to ProQuest
Al Noman, Md Nayeem, "Ground Motion Prediction Modeling and Seismic Lg Wave Attenuation Tomography" (2023). Electronic Theses and Dissertations. 3097.