Does Chatham, IL need an earthquake retrofit?

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Chatham in Seismic Design Category C: Moderate seismic hazard. Code adds irregular-building restrictions and requires bracing of some nonstructural components (e.g. tall shelving, water heaters) in addition to structural detailing. That puts Chatham in the 70th percentile nationally for seismic hazard - higher than 70% of the 4,875 US cities USGS was checked against here.

How Chatham compares

The raw figures: peak ground acceleration 0.103g, short-period spectral response 0.21g, 1-second spectral response 0.105g. Among 330 Illinois cities in this dataset, Chatham ranks 53 for seismic hazard, the 84th percentile within the state. About 14,639 people live in Chatham, Illinois.

Bracing and bolting: the actual cost

Outside California, no state-level retrofit grant equivalent to Brace + Bolt could be found for Illinois. A typical retrofit still runs $5,000-$10,000 nationally, about $7,000 for a common single-family job.

Insuring against this, not just retrofitting

Outside California, earthquake coverage is typically sold as an endorsement added to a standard homeowners policy, not a separate product - worth asking about directly when getting a home-insurance quote for a Chatham address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Chatham's numbers. The guide to what a Seismic Design Category actually means covers why a category is never a substitute for an engineer's assessment of one specific house.