Controls on ground surface deformation in thrust and reverse fault earthquakes

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Ground surface rupture during large earthquakes poses significant hazards to urban environments, critical information and energy transmission infrastructure, transportation systems, as well as other sensitive facilities in the United States and other parts of the world. This research will develop a robust physical understanding of the factors that control the style, distribution, and intensity of ground surface ruptures during thrust and reverse faults earthquakes. This will provide a basis for better forecasting the patterns of ground surface deformation during future earthquakes, with the goal of helping to reduce the loss of life and property. The research will also support the training of undergraduate and graduate students, and research results will be incorporated in new college classes, K-12 education programs, and public outreach through the Harvard Museum of Natural History.The study will employ the discrete element method (DEM) to generate a large suite of 2-dimensional models (~6,000) that will identify the role of various properties (e.g., fault dip, sediment strength, sediment thickness) in controlling the patterns of ground surface deformation. In addition, the study will develop 3-dimensional models that address inherent variability in surface deformation patterns along strike. The DEM method is well suited to this purpose as it effectively reproduces both the geologic processes of faulting and folding at depth, as well as the granular mechanics of soil and sediment deformation in the shallow subsurface. DEM enables the development of emergent features, such as fractures/fissures, secondary faults, flexural slip surfaces, and folds that comprise ground surface deformation patterns during large earthquakes. By systematically varying fault and sediment parameters in their models, the researchers will develop a mechanics-based understanding of controls on ground surface rupture patterns that can help to assess site-specific hazards. Through large suites of models, they will statistically assess the patterns of ground surface deformation to inform and enhance Probabilistic Fault Displacement Hazard Analysis (PFDHA) methods. PFDHA is established as the standard for hazard forecasting related to ground surface rupture, but is particularly challenged by thrust and reverse fault earthquakes due to the complexity of these ruptures and the paucity of historic events to use for calibration. Their results will provide a robust database to assess how slip at depth is manifest in both direct fault displacements and distributed ground surface deformation. This will help to calibrate PFDHA methods used in forecasting rupture locations, displacements, and other characteristics that pose risks to critical infrastructure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.