MAKING THE CASE FOR SEISMIC HAZARD ASSESSMENT ACROSS THE MIDCONTINENT: AN EXAMPLE FROM CINCINNATI, OHIO

In the continental U.S. seismic hazard assessment is rightfully focused in areas of the greatest seismicity and highest probability of destructive events, namely in the west. In the midcontinent, most work focuses on areas with historic large-magnitude events, recent moderate events, and areas of induced seismicity. However, the potential for damage from one of these events is more widespread than for a similar-scale event in the west. Additionally, many areas of the midcontinent are becoming more exposed to potential induced seismicity numerous new and planned CO₂ and brine injection wells and fields across the area. Also, the prevalence of unreinforced masonry and other building types with poor resistance to shaking across much of the midcontinent lead to increased likelihood of increased building collapse, economic losses, and fatalities. Therefore, it is critical that we improve seismic hazard evaluation across the entire midcontinent, especially in the major urban areas.

For example, Cincinnati, Ohio does not have significant nearby faults, but large historic earthquakes (including the New Madrid earthquake sequence) caused damage in (a much smaller) Cincinnati. Today, the Cincinnati metro area has a population exceeding 2.25 million, and a New Madrid-type earthquake would likely cause significant, widespread damage across the metro area. The complex near-surface geology in the Cincinnati area likely will result in spatially variable shear wave velocities and shaking hazards. Some of the Cincinnati area sits on bedrock exposures, dominated by resistant Ordovician limestones and weak shales. However, Cincinnati sits just south of the southern margin of Wisconsinan glaciation and just north of the southern margin of Illinoian glaciation. Many glacial outwash-related fluvial systems are partially filled with unconsolidated sediment and now provide pathways for streams and rivers in the region. Some areas with the thickest glacial drift are fully buried 1-3 km wide sinuous valleys filled with more than 100 m of unconsolidated till. We will discuss early results from an MASW study in the Cincinnati region to evaluate variation in shear wave velocities across the Cincinnati region and discuss lessons learned for similar small-scale studies in other midcontinent cities.