Comparisons of FDHI fault displacement models for principal and aggregate displacement

Abstract

The data sets, model formulations, and results from four new fault displacement models (FDMs) developed through the Fault Displacement Hazard Initiative (FDHI) Project are summarized and compared with each other and previously published FDMs. The models were developed using the new FDHI Database and provide predictions for principal or aggregate surface fault displacement, where aggregate is the combined displacement across principal and distributed ruptures. Different definitions of displacement are used among the models, and the differences should be considered when comparing model predictions or using multiple models in a logic tree. All new models are applicable between M 6.0 and 8.0, although some are also applicable to lower or higher magnitudes. Two models were developed for all styles of faulting, while the other two only apply to a single style. Quantitative comparisons are provided for a range of scenarios defined by style of faulting, magnitude, and normalized along-strike location. Average displacement predictions in the new models are within a factor of about 1.5 for most magnitudes and styles of faulting. Upper tail (i.e. 99th percentile) predictions in the new models are within a factor of about 2.5 in most cases. Compared to previously published models, average displacements in the new models are about 40% higher for M∼7, whereas upper tail predictions are up to six times lower. Key features of the new models include the use of a large, high-quality empirical database and improved modeling of the magnitude scaling and aleatory variability. Together, these lead to upper tail predictions that are in reasonable agreement with empirical observations of maximum displacement for large magnitudes, which supports the use of the FDHI FDMs in probabilistic fault displacement hazard analysis (PFDHA) at long return periods.