street. LOUIS - USGS simulations and research indicate that St. Louis faces a small but real risk of a moderate to strong earthquake in the future, a probability of no more than 2% over the next 50 years.
The greater St. Louis area is at risk not only from earthquakes in the New Madrid and Wabash Valley seismic zones, but also from smaller pockets of historical seismic activity closer to the south and east of St. Louis.
Three USGS maps (included in the slideshow below) simulate potential earthquake scenarios for the St. Louis area.
The first map shows the ground shaking for one second, projecting "all estimates of possible future earthquakes." The second map shows the Modified Mercalli Intensity (MMI) hazard from a hypothetical magnitude 6.0 earthquake at Shoal Creek, about 40 miles east of St. Louis in southern Illinois. The third map shows the peak ground acceleration (PGA) based on the same hypothetical magnitude 6.0 earthquake.
Three USGS maps simulate potential earthquake scenarios for the St. Louis area. (Map provided by: US Geological Survey)
Three USGS maps simulate potential earthquake scenarios for the St. Louis area. (Map provided by: US Geological Survey)
Three USGS maps simulate potential earthquake scenarios for the St. Louis area. (Map provided by: US Geological Survey)
Inevitably, damage will vary widely across the city of St. Louis and the St. Louis region. It is unclear which locations could be most affected. However, USGS models provide insight into likely scenarios if a magnitude 6.0 (or higher) earthquake occurs in or near St. Louis.
Structures in low-lying areas along the Missouri and Mississippi River floodplains, especially in communities built on thick, soft sediments, are more likely to experience stronger earthquakes, the USGS says. Communities near the confluence of the two rivers, including Granite City, Wood River and Spanish Lake, could see notable infrastructure damage due to suddenness, and flood risks could evolve over time based on impacts to levees, roads and other critical systems.
Conversely, elevated structures outside floodplains, especially those built on bedrock, will experience lower levels of prolonged seismic shaking. However, these structures can feel high-frequency vibrations for shorter periods, which may affect buildings with less flexible materials and compositions, such as those made of brick and older masonry.
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On the MMI map, the St. Louis area is mostly in the sixth to eighth range, indicating at least moderate structural damage. In practice, this may mean clusters of buildings with cracked walls, falling objects and structural damage, and is perhaps more likely for older and poorly maintained buildings. Bridges can also experience fatigue or partial failure, especially those that have not been modified and retrofitted for seismic activity.
Meanwhile, the PGA map shows ground shaking forces of 0.1-0.5 g over much of the St. Louis metropolitan area. In general, the lower the ratio, the less stress your buildings and landscape may experience. For St. Louis, unless a large earthquake is centered closer to the city than Shoal Creek, models indicate moderate shaking, but structures built to modern seismic standards will likely remain intact.
A 2004 report cited by the Missouri Department of Natural Resources estimates that a large earthquake, a magnitude 7.7 for example, could cause more than $69 billion in damage to more than 87,000 buildings in the state. Adjusted for recent inflation, those numbers are likely to be higher, but that will also depend on which parts of the state took the biggest direct hits.
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