Spearfish's Seismic Design Category, explained

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Spearfish in Seismic Design Category A: Lowest seismic design category. Building code requires no seismic-specific detailing here beyond ordinary construction practice. Nationally, Spearfish ranks above 15% of the 4,875 cities in this dataset for seismic hazard - the 15th percentile.

Spearfish by the numbers

USGS's underlying values for Spearfish: 0.062g peak ground acceleration, 0.125g at short period, 0.04g at 1 second. Within South Dakota alone, Spearfish ranks 5 of 18 cities by seismic hazard - the 76th percentile in-state. Spearfish has a population of about 13,803.

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.

What this means for insurance

A Spearfish 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 Spearfish's figures come from

Spearfish'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 Spearfish.