Madison, SD: what USGS's seismic model says

Madison carries Seismic Design Category A under USGS's ASCE 7-16 model. 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 Madison sits at the 15th percentile for seismic hazard among 4,875 US cities.

How Madison compares

USGS's underlying values for Madison: 0.051g peak ground acceleration, 0.101g at short period, 0.028g at 1 second. Within South Dakota alone, Madison ranks 10 of 18 cities by seismic hazard - the 47th percentile in-state. Madison has a population of about 6,086.

Bracing and bolting: the actual cost

A full earthquake retrofit typically runs $5,000-$10,000 nationally (around $7,000 typical), driven mainly by house size and foundation type, not by South Dakota specifically. California's Earthquake Brace + Bolt grant, which covers a large share of this cost, is a California-only program and does not apply in South Dakota.

Insuring against this, not just retrofitting

A Madison homeowner cannot buy a standalone earthquake policy in most cases - it is added to an existing homeowners policy as an endorsement, so the place to start is a regular home-insurance quote.

Where Madison's figures come from

Madison's Category A and every number above trace to USGS's own ASCE 7-16 Design Maps service - see the methodology guide. See the category explainer for what Category A does and doesn't tell you about Madison.