Does Lewistown, MT need an earthquake retrofit?

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

Lewistown by the numbers

The raw figures: peak ground acceleration 0.05g, short-period spectral response 0.103g, 1-second spectral response 0.047g. Among 19 Montana cities in this dataset, Lewistown ranks 16 for seismic hazard, the 17th percentile within the state. About 6,204 people live in Lewistown, Montana.

Retrofit economics for Lewistown

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

Earthquake insurance for a Lewistown home

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 Lewistown address.

More on how this number was built

The methodology guide covers exactly how USGS's public design-maps API produced Lewistown'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.