Does Rapid City, SD need an earthquake retrofit?

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Rapid City in Seismic Design Category A: Lowest seismic design category. Building code requires no seismic-specific detailing here beyond ordinary construction practice. Rank it against the rest of the country and Rapid City sits at the 16th percentile for seismic hazard among 4,875 US cities.

How Rapid City compares

The raw figures: peak ground acceleration 0.071g, short-period spectral response 0.139g, 1-second spectral response 0.041g. Among 18 South Dakota cities in this dataset, Rapid City ranks 3 for seismic hazard, the 88th percentile within the state. About 79,894 people live in Rapid City, South Dakota.

What a retrofit costs in Rapid City

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.

Earthquake insurance for a Rapid City home

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 Rapid City address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Rapid City'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.