Does Yankton, SD need an earthquake retrofit?

Under the seismic model IBC and ASCE 7 use for new construction, Yankton is Category A. Lowest seismic design category. Building code requires no seismic-specific detailing here beyond ordinary construction practice. That puts Yankton in the 15th percentile nationally for seismic hazard - higher than 15% of the 4,875 US cities USGS was checked against here.

Where Yankton sits in South Dakota

The raw figures: peak ground acceleration 0.058g, short-period spectral response 0.113g, 1-second spectral response 0.039g. Among 18 South Dakota cities in this dataset, Yankton ranks 7 for seismic hazard, the 65th percentile within the state. About 15,670 people live in Yankton, South Dakota.

What a retrofit costs in Yankton

Outside California, no state-level retrofit grant equivalent to Brace + Bolt could be found for South Dakota. A typical retrofit still runs $5,000-$10,000 nationally, about $7,000 for a common single-family job.

What this means for insurance

Outside California, earthquake coverage is typically sold as an endorsement added to a standard homeowners policy, not a separate product - worth asking about directly when getting a home-insurance quote for a Yankton address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Yankton's numbers. The guide to what a Seismic Design Category actually means covers why a category is never a substitute for an engineer's assessment of one specific house.