Harrisburg's Seismic Design Category, explained

Harrisburg carries Seismic Design Category D under USGS's ASCE 7-16 model. High seismic hazard - this is the category most of coastal California, the Pacific Northwest, and other active fault regions fall into. Code mandates significant seismic detailing and restricts irregular structural configurations. This is the category the Brace + Bolt scope (cripple-wall bracing, foundation bolting) is built for. That puts Harrisburg in the 88th percentile nationally for seismic hazard - higher than 88% of the 4,875 US cities USGS was checked against here.

How Harrisburg compares

USGS's underlying values for Harrisburg: 0.433g peak ground acceleration, 0.733g at short period, 0.246g at 1 second. Within Illinois alone, Harrisburg ranks 5 of 330 cities by seismic hazard - the 99th percentile in-state. Harrisburg has a population of about 7,937.

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 Illinois 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 Illinois.

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 D 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 D does and doesn't tell you about Harrisburg.