Philadelphia's Seismic Design Category, explained

Under the seismic model IBC and ASCE 7 use for new construction, Philadelphia is 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 Philadelphia in the 68th percentile nationally for seismic hazard - higher than 68% of the 4,875 US cities USGS was checked against here.

Where Philadelphia sits in Mississippi

The raw figures: peak ground acceleration 0.083g, short-period spectral response 0.17g, 1-second spectral response 0.094g. Among 61 Mississippi cities in this dataset, Philadelphia ranks 28 for seismic hazard, the 55th percentile within the state. About 6,938 people live in Philadelphia, Mississippi.

Retrofit economics for Philadelphia

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

What this means for insurance

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 Philadelphia address.

More on how this number was built

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