Earthquake-induced soil liquefaction is a phenomenon in which saturated, sandy soil loses its strength and stiffness during earthquake shaking. Liquefaction can be extremely costly and damaging to infrastructure. The commonly used "simplified" stress-based liquefaction triggering framework is correlated with metrics computed from in-situ tests like the Cone Penetration Test (CPT). While CPT-based procedures have been shown to accurately predict liquefaction occurrence in homogenous, sandy soil profiles, they tend to over-predict the occurrence of liquefaction in challenging, highly interlayered soil profiles. One contributing factor to the over-prediction is multiple thin-layer effects in CPT data, a phenomenon in which data in interlayered zones is blurred or averaged, making it difficult to identify specific layer boundaries and associated CPT parameters like tip resistance. Multiple thin-layer correction procedures have been proposed to convert the measured tip resistance in an interlayered profile (qm) to the "true" or characteristic tip resistance (qt) that would be measured without the influence of multiple thin-layer effects. In this dissertation, the efficacy of existing multiple thin-layer correction procedures is assessed. It is shown that existing procedures are not effective for layer thicknesses equal to or less than about 1.6 times the diameter of the cone. Two new multiple thin-layer correction procedures are proposed. Furthermore, a framework for numerically simulating CPTs in interlayered soil profiles using the Material Point Method (MPM) is developed. A framework for linking uncertainties associated with the numerical analyses and the laboratory CPT calibration chamber tests used to calibrate the numerical analyses is also proposed. Finally, a database of laboratory and numerically-generated CPT data is presented. It is shown how this database can be used to improve existing, and develop new, multiple thin-layer correction procedures. Ultimately, the work detailed in this dissertation will improve the characterization of highly interlayered soil profiles using CPTs to support more accurate liquefaction hazard assessment at challenging soil sites. / Doctor of Philosophy / Earthquake-induced soil liquefaction is a phenomenon in which saturated, sandy soil loses its strength and stiffness during earthquake shaking. Liquefaction can be extremely costly and damaging to infrastructure. Existing procedures used to assess liquefaction hazard were developed specifically for homogenous, sandy soil profiles. These procedures do not perform well in challenging, highly interlayered soil profiles. One reason for this is the inadequate characterization of the soil profile by the chosen in-situ test method. For example, the cone penetration test (CPT) consists of hydraulically advancing a steel probe with a conical shaped tip ("cone") into the ground. Typically, the penetrometer is about 3.6 to 4.4 cm in diameter, and data are recorded at 1 to 5 cm depth intervals. However, data recorded at a specific depth are representative of soil that falls within a zone several times the diameter of the penetrometer ahead of and behind the tip of the cone. In a highly interlayered soil profile, this means the CPT records blurred or averaged data within interlayered zones. Typical liquefaction analyses compute a factor of safety against liquefaction at every depth in the soil profile where CPT data are recorded. Hence, having data that are blurred can result in an inaccurate factor of safety against liquefaction. To account for this blurring (called multiple thin-layer effects), correction procedures have been proposed. This dissertation evaluates the effectiveness of those procedures and develops new procedures. Additionally, a numerical simulation tool is shown to be capable of simulating CPTs in layered soil profiles. This reduces the need for costly laboratory testing to further evaluate multiple thin-layer effects. Finally, a combined laboratory and numerically-generated CPT database is developed to support the improvement of, and development of new, multiple thin-layer correction procedures. The broader impacts of this work support more accurate liquefaction evaluations in challenging soil profiles worldwide, like those in Christchurch, New Zealand, and the Groningen region of the Netherlands.