Systems Thinking and Decision Making versus Location-Specific Approaches in Co-Seismic Slide Masses—Examples for Designers from the Farmington Siding Complex

The Farmington Siding Landslide Complex is a mapped paleo coseismic landslide in Davis County, Utah, that extends several kilometers beneath heavily developed urban and suburban areas. In design and development of new infrastructure on the complex, there are implications for systems thinking decision approaches for analyzing and mitigating the extreme event hazards versus location or project-specific approaches. Typical landslides or lateral spreads are commonly limited to areas that are a few tens to hundred meters across and systems approaches are not warranted due to the small spatial extents. When dealing with landslides that are several kilometers in width, the implications of compounding effects and unintended consequences of design decisions become pronounced. For example, if a new highway bridge is constructed in the area, how will potential ground improvements to protect individual bridges be designed to resist such large spatial impacts? How will the new highway affect the impacts to pre-existing infrastructure? Are the costs to keep a bridge standing warranted when there will be no undamaged or usable roads to access the bridge? Concepts of performance-based design and resilience enter into these decision-making processes. We use the Farmington Siding Landslide Complex as a canvas on which to discuss these different approaches and the impacts of different decisions both on single site projects and the system as whole.