Portsmouth, NH: what USGS's seismic model says

USGS's ASCE 7-16 seismic design model - the same standard building codes use - places Portsmouth 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. Nationally, Portsmouth ranks above 77% of the 4,875 cities in this dataset for seismic hazard - the 77th percentile.

Portsmouth by the numbers

The raw figures: peak ground acceleration 0.203g, short-period spectral response 0.329g, 1-second spectral response 0.075g. Among 13 New Hampshire cities in this dataset, Portsmouth ranks 8 for seismic hazard, the 42th percentile within the state. About 22,938 people live in Portsmouth, New Hampshire.

Retrofit economics for Portsmouth

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

Earthquake insurance for a Portsmouth 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 Portsmouth address.

More on how this number was built

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