A USGS earthquake report is a catalog solution, not a single instrument reading. It combines a preferred event origin, magnitude, depth, timestamps, review state and links to optional products. Early values can change. Reading the type and update time prevents many common mistakes.
Quick answer
| Field | What it means | What it does not mean |
|---|---|---|
time |
Estimated rupture origin time | Publication time |
updated |
Last source update timestamp | Event duration |
mag / magType |
Preferred magnitude and method | Local intensity or damage |
| coordinates / depth | Preferred hypocenter | Full fault rupture |
status |
Automatic or reviewed workflow state | Guaranteed finality |
mmi |
Maximum instrumental intensity from ShakeMap | Magnitude or an intensity at every location |
cdi |
Maximum reported intensity from Did You Feel It? | Instrumental measurement |
alert |
PAGER impact-alert color when available | Official local order |
tsunami |
Flag for large events in oceanic regions | Confirmation that a tsunami occurred or will occur |
Core catalog fields
The place string usually describes distance and direction from a recognizable locality. It is generated for orientation and is not a legal boundary or a claim that the epicenter lies inside that city.
Magnitude needs its type. Mw, ML, mb and other codes use different observations. Depth belongs to the hypocenter and may be less certain than horizontal position. The event type distinguishes earthquakes from quarry blasts, explosions and other cataloged phenomena.
Origin time is normally shown in UTC for global comparison. Local time requires the correct time zone at the event location, including historical daylight-saving rules.
Status, updates and identifiers
An event ID is the stable handle used to link revisions and products. A feed entry can update its location, magnitude, type, place, status and product availability while retaining that ID. Separate network IDs can sometimes be associated with the same physical event.
automatic means software published the solution before analyst review. reviewed means an analyst examined it, but later changes remain possible. The update timestamp tells when the source last changed the record; it should not replace origin time in a timeline.
Earthquake24 keeps the source ID and links back to the original record. Its methodology explains validation, versioning and freshness.
ShakeMap, MMI and PAGER
ShakeMap combines measured and modeled ground motion to represent shaking across a region. MMI is intensity at locations, not the event’s magnitude. cdi is the maximum reported intensity from Did You Feel It?; it depends on participation.
PAGER uses ShakeMap, population exposure and vulnerability models to estimate ranges of fatalities and economic losses. Green, yellow, orange and red indicate increasing modeled alert levels. They are rapid, uncertain impact estimates—not casualty counts, magnitude classes or local instructions.
sig is a USGS significance score used for catalog ranking and includes several inputs. It is not a universal scientific hazard scale.
Limits and common mistakes
Missing does not mean zero. A blank PAGER, MMI, felt-report or tsunami product can mean it was not supplied or applicable in that feed. Never turn absence into a confirmed negative fact.
Marker size represents magnitude only on Earthquake24; it does not show affected area. A source flag may point to another product but does not reproduce its full status. Open the original record for the latest source context.
Common questions
Why did the magnitude change?
More stations, new phase picks or a different preferred magnitude method produced a revised solution.
What is the difference between mmi and cdi?
mmi is the maximum instrumental intensity from ShakeMap; cdi is the maximum reported intensity from Did You Feel It? Neither is a single intensity experienced everywhere. Availability varies.
Does “reviewed” mean final?
No. It records workflow review, not a guarantee against future correction.
Why is PAGER missing?
PAGER is produced for qualifying events and depends on available products. Missing should be displayed as not supplied, not as green or zero impact.