Northfield's Seismic Design Category, explained

Northfield carries Seismic Design Category B under USGS's ASCE 7-16 model. Low seismic hazard. Code requires basic seismic detailing (bracing, connections) but no special structural system restrictions. Nationally, Northfield ranks above 33% of the 4,875 cities in this dataset for seismic hazard - the 33th percentile.

Northfield by the numbers

USGS's underlying values for Northfield: 0.055g peak ground acceleration, 0.11g at short period, 0.06g at 1 second. Within Illinois alone, Northfield ranks 282 of 330 cities by seismic hazard - the 15th percentile in-state. Northfield has a population of about 5,625.

Retrofit economics for Northfield

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 Northfield 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 Northfield's figures come from

Northfield'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 Northfield.