A significant earthquake is not defined by magnitude alone. The USGS significance value incorporates factors that can include magnitude, the number and strength of Did You Feel It responses, and PAGER alert information.
This makes the significant filter useful for finding events that attracted attention or may have meaningful impact context. It should still be read with the official event products, local authority information, and the current record status.
What USGS earthquake significance means
Significance is a ranking aid within the earthquake catalog. A moderate earthquake widely felt near a populated area may receive a different significance score from a larger remote event. The score helps surface notable records, but it is not a universal damage scale and does not replace alert or intensity products.
Magnitude, intensity, alerts, and significance
Magnitude measures source size. Intensity describes shaking at particular locations. PAGER estimates population exposure and possible consequences using available models and data. Significance can use several of these signals, so readers should not substitute one term for another.
Missing impact products should not be interpreted as proof that no effects occurred, especially while a recent record remains preliminary.
Using the significant-only filter responsibly
The tracker applies a documented significance threshold to the current USGS result set. Because feed values can change, the list may change after review. For a formal catalog query or historical analysis, use the official USGS search tools and record the search parameters.