Safety first
- QuakeWatch does not predict earthquakes. No one can reliably predict them.
- Alerts in QuakeWatch are application notifications, not emergency warnings. They may be delayed by USGS publication and by polling.
- Official agencies remain authoritative. Follow your national or local emergency guidance; in supported regions ShakeAlert provides real earthquake early warning.
- The USGS tsunami flag means tsunami information may exist for an event — it is not a tsunami warning.
Data source
Earthquake data courtesy of the U.S. Geological Survey (USGS). QuakeWatch reads the public USGS real-time GeoJSON summary feeds every few minutes and imports history through the USGS FDSN event catalogue (magnitude 2.5 and above). Scientific product details (ShakeMap, PAGER, DYFI and others) are fetched from the USGS detail feed for important events or on request. QuakeWatch surfaces these products; it does not produce competing impact estimates.
Revision tracking
USGS updates events after they are first published: magnitudes are recalculated, locations refined, and automatic solutions are reviewed by analysts. QuakeWatch keeps every meaningful change as an immutable revision. A new revision is stored only when a tracked field changes by more than its tolerance (for example 0.005 in magnitude, 0.1 km in depth, about 111 m in location), so floating-point noise is not recorded as a change. The policy is versioned and every revision records the policy version that produced it.
Source values vs derived values
Values from USGS are stored unchanged. Values QuakeWatch computes — the region name (taken from the text after the last comma of the USGS place description), first-observation latency and analytics — are stored separately, labelled as derived, and never overwrite source values.
Freshness and gaps
Every page shows how recently the live feed was synchronised. If QuakeWatch is not polling (maintenance, network or USGS outages), events that occur during the gap are picked up by later syncs, but timing statistics that depend on when QuakeWatch observed an event can be affected. Where possible, metrics use USGS timestamps instead, and each metric states its definition. See System status.
Coverage
The historical import includes magnitude 2.5 and above. Smaller events are present only from the start of live monitoring, which is dense in regions with local seismic networks (for example California and Alaska) and sparse elsewhere. Counts describe QuakeWatch's copy of the catalogue, not the complete global record.
Reproducible research datasets
A research snapshot freezes the events matching a query at their current revisions, computes a SHA-256 checksum over the rows and stores a manifest with the query, application and schema versions and the USGS requests that produced the data. Re-downloading a snapshot always returns identical rows.