Portsmouth's Seismic Design Category, explained

Under the seismic model IBC and ASCE 7 use for new construction, Portsmouth is Category A. Lowest seismic design category. Building code requires no seismic-specific detailing here beyond ordinary construction practice. That puts Portsmouth in the 14th percentile nationally for seismic hazard - higher than 14% of the 4,875 US cities USGS was checked against here.

Portsmouth by the numbers

USGS's underlying values for Portsmouth: 0.043g peak ground acceleration, 0.089g at short period, 0.04g at 1 second. Within Virginia alone, Portsmouth ranks 60 of 63 cities by seismic hazard - the 5th percentile in-state. Portsmouth has a population of about 96,482.

Retrofit economics for Portsmouth

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 Virginia 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 Virginia.

What this means for insurance

A Portsmouth 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 Portsmouth's figures come from

Portsmouth's Category A 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 A does and doesn't tell you about Portsmouth.