Harrisburg's Seismic Design Category, explained

Under the seismic model IBC and ASCE 7 use for new construction, Harrisburg is Category A. Lowest seismic design category. Building code requires no seismic-specific detailing here beyond ordinary construction practice. Nationally, Harrisburg ranks above 14% of the 4,875 cities in this dataset for seismic hazard - the 14th percentile.

Harrisburg by the numbers

USGS's underlying values for Harrisburg: 0.044g peak ground acceleration, 0.09g at short period, 0.036g at 1 second. Within South Dakota alone, Harrisburg ranks 14 of 18 cities by seismic hazard - the 24th percentile in-state. Harrisburg has a population of about 10,203.

Retrofit economics for Harrisburg

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 Harrisburg 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 Harrisburg's figures come from

Harrisburg'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 Harrisburg.