Spring Grove, IL: what USGS's seismic model says

Under the seismic model IBC and ASCE 7 use for new construction, Spring Grove is Category B. Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. That puts Spring Grove in the 30th percentile nationally for seismic hazard - higher than 30% of the 4,875 US cities USGS was checked against here.

Spring Grove by the numbers

USGS's underlying values for Spring Grove: 0.05g peak ground acceleration, 0.1g at short period, 0.056g at 1 second. Within Illinois alone, Spring Grove ranks 317 of 330 cities by seismic hazard - the 4th percentile in-state. Spring Grove has a population of about 5,554.

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 Spring Grove 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 Spring Grove's figures come from

Spring Grove's Category B 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 B does and doesn't tell you about Spring Grove.