Ashly Cabas

This CAREER proposal will create a new multiscale probabilistic approach to quantify the response of sedimentary deposits to earthquake ground shaking (site response) in highly uncertain environments. Efforts toward improving resiliency of urban environments are challenged by variable seismic demands over large areas (e.g., the city of Los Angeles or along the alignment of distributed infrastructure such as pipelines), geohazards, and uncertainties associated with system-level performance (e.g., lifelines networks). Drinking water and wastewater utilities are critical lifelines after seismic events because of the potential impairment of the ability to fight fires, and negative effects of earthquake damage on public health, and the environment. Hence, this CAREER proposal focuses on water supply distribution systems (WSDS) and the challenges in incorporating multiscale modeling of site response into their seismic hazard assessments. Numerical modeling, geospatial analytics and uncertainty quantification will be used to develop the first conditional site amplification functions at local and regional scales that incorporate available data, spatial correlations, and uncertainty. Bayesian Networks (BN) and decision-support tools will enable the otherwise computationally costly system-level probabilistic seismic hazard analysis (multi-site PSHA) to be applied to WSDS. The proposed work is important because incorporating a robust regionalization of site effects into an optimized probabilistic approach that accounts for uncertainty has the potential to transform seismic hazard assessments of WSDS. This work is urgently needed in other highly uncertain environments (i.e., with scarcity of data) in the US (e.g., central and eastern US) and other earthquake-prone regions, such as mega-cities in Latin America. Thus, the educational and outreach goal of this work is to consolidate retention strategies for, and broaden participation from, women and Latin American students in STEM through a multifaceted educational plan that includes the launch of the Earthquake Engineering and Seismology Community Alliance in Latin America (E2SCALA) program.

This proposal aims to develop a rapid seismic bridge assessment method that can be used for planning (via scenarios), and for post-earthquake assessment (inspection prioritization). Unlike existing methods which are largely probabilistic, and focused on high level assessment, the proposed methodology is sufficiently versatile that it can provide a range of information, spanning from deterministic bridge specific performance, to broader assessments of bridge vulnerability. The procedure relies upon the Direct Displacement-Based Design approach as the analysis engine, and has three components: (1) Bridge metadata; (2) Bridge limit state parameters; and (3) Seismic Hazard characterization. Given any 2 of the above, the third may be determined. While the approach will function with very course data (i.e. basic metadata such as span lengths, column diameter, and height; basic limit state parameters, such as limit state displacement; and course hazard definition (such as a 3 point code-based spectra), with more detailed information, the fidelity of the outcome increases significantly. The work described in this proposal will define limit state parameters for Alaska bridges and characterize the seismic hazard. The framework for the rapid assessment approach will also be developed and applied to a series of bridges. The final outcome will be detailed plans for development of a rapid assessment application which would be developed in a future phase of the research.

Liquefaction-induced large lateral displacements (i.e., lateral spreading) after earthquakes represent a major geohazard in earthquake-prone regions leading to significant human and economic costs. This one-year collaborative proposal by North Carolina State University and Bucknell University aims to improve the prediction of liquefaction-induced lateral spreading. In pursuit of that goal, we aim to (1) incorporate geomorphic factors that control large lateral displacements (LD) into empirical predictive models, (2) define an improved ground motion (GM) characterization that includes the duration of ground shaking and the time to the onset of liquefaction triggering, and (3) reduce bias and variability in lateral spreading predictions. The outcome of the proposed work will be a framework that incorporates relevant geomorphic variables in lateral spreading models.

Previous research on earthquake ground motions along the Atlantic and Gulf Coastal Plains show significant frequency-dependent deviations in site response relative to other areas in the Central and Eastern United States (CEUS). For instance, amplitudes and durations of ground motions are shown to be strongly correlated with sediment thickness. Even though regional site response models are available for the region, the ones that account for sediment thickness only capture linear amplifications and fail to constrain the uncertainty in velocity models. This project addresses this gap by incorporating nonlinear soil behavior at a regional scale and fully incorporating it into a probabilistic seismic hazard analysis. This work will have a significant impact on the next National Seismic Hazard Maps.

The main objective of this study is to improve current definitions of host and target site-specific attenuation in partially nonergodic probabilistic seismic hazard analysis (PSHA). Site-specific attenuation is often defined by means of the spectral decay parameter kappa, but ther is currently no consistent/compatible attenuation models for the host a target regions. The main challenge is the lack of data in low to moderate seismicity regions (i.e., target regions), which does not allow the use of the acceleration spectrum methodology to compute kappa (as it is often use for the host regions). Additionally, a novel model for kappa values is proposed, so that the contributions from the attenuation experienced in the rock mass and the overlying soil profile can be treated separately. This decomposition could prove very useful in partially nonergodic PSHA. Finally, our current understanding of kappa from a geotechnical engineering perspective will be improved by further decomposing the kappa value corresponding to the soil profile into material damping and scattering contributions.

The importance of properly characterizing ground-motion intensity measures for seismic hazard assessment is unequivocally large. However, only a few studies have investigated the degree to which the uncertainty resulting from traditional input motion selection protocols introduces errors in the estimation of ground-motion intensity measures at the surface. This study will compare current practices for input motion selection, identify shortcomings in these practices, and investigate their impact on the uncertainty in ground-motion intensity measures. Moreover, recommendations for improvements to existing input motion selection procedures will be proposed. Comprehensive ground response analyses at two representative sites, one in the western United States (WUS: California) and one in the central and eastern United States (CEUS: Boston, Massachusetts), will be performed. These two sites not only represent different geological and geotechnical conditions, but different levels of seismicity: the WUS site is in a region of high seismicity in which a small number of faults dominates the hazard, and the CEUS site is in a region of moderate seismicity in which the sources of hazard are much more diffuse.

The overarching goal of this project is not only to enhance the project leader??????????????????s professional network and potential for new collaborations, but also to broaden the research program at North Carolina State University (NCSU). The proposed project will have two stages. First, a three-day visit of the project leader to the University of Texas at Austin (UT Austin), and a subsequent visit of Professor Ellen Rathje to NCSU. During the first stage, discussions on the project leader??????????????????s National Science Foundation (NSF)CAREER proposal will take place, as well as a laboratory tour to provide guidance on the purchase of a resonant column and torsional shear device. Networking opportunities with Dr. Rathje??????????????????s research group and other faculty members at UT Austin will also be included in this first stage. Professor Rathje??????????????????s visit to NCSU will foster more collaboration opportunities as follow-up discussions on research projects develop. She will be able to provide feedback on the progress of graduate student members in the geotechnical earthquake engineering research group at NCSU, and will participate as the guest speaker at a graduate seminar. Additionally, Prof. Rathje will also interact with the geotechnical engineering female faculty at NCSU at a special networking event.