Technical
Coverage area and data sources
Which earthquakes we report on, the places we estimate intensity for, and the data and models behind the estimates.
Where we cover
An earthquake is covered when three conditions hold:
- The USGS reports it at magnitude 3.5 or above.
- Its epicenter lies inside the coverage region, 28–49°N and 113–125°W.
- Its USGS ShakeMap reaches at least one of our 2,002 named places. An offshore event whose shaking reaches no named place is not reported.
The named places are communities of roughly 1,000 or more residents, drawn from the GeoNames gazetteer: California (1,114), Washington (401), Oregon (220), northern Baja California and Sonora (101), western Idaho (100) and Nevada (66). Browse the places →
On each event page we list every place estimated at intensity IV or above, and always at least three. Animations are made for events whose strongest estimated shaking reaches intensity V.
What it runs on
Intensity Lab computes Modified Mercalli Intensity (MMI) estimates. Estimated shaking comes from USGS ShakeMap, which combines station recordings, Did You Feel It? reports and ground motion models, with independent estimates from four NGA-West2 ground motion models computed with GEM OpenQuake. Site conditions (Vs30) come from California's geology-based values through the SCEC Unified Community Velocity Model, and elsewhere from the USGS Wald & Allen model. The simulated seismograms behind the animations are computed on the SCEC Broadband Platform through the BBP Services API.
The shaking videos are not limited to this region: they are camera footage of strong earthquakes anywhere in the world, found through USGS event data and published video, each credited to its source.