Read and audit an earthquake catalog snapshot

Begin with the record behind the number

This investigation uses three real historical event estimates from the USGS earthquake catalog: Tohoku 2011, Nepal 2015 and Ridgecrest 2019. The short labels are editorial conveniences. The preserved source identifiers, place descriptions and timestamps identify the records more precisely. These are deliberately selected examples, not synthetic earthquakes and not a complete or random sample of earthquake activity.

The local snapshot is named earthquake-catalog-v1 and was retrieved at 2026-10-25T18:59:12Z. Its stored magnitudes are 9.1, 7.8 and 7.1 respectively. The browser compares this saved version; opening a source page later can show revised information. Retaining a version and retrieval time makes a calculation reproducible even if the external catalog changes.

Choose each event in turn. In a paper ledger, record its short label, source identifier, magnitude value and magnitude type. Place a separate heading over the derived ratios. That separation makes clear which numbers were supplied by the catalog and which were calculated by the lesson.

Distinguish three kinds of time

The origin time estimates when the event began. The catalog-updated timestamp records when the event record was updated. The snapshot retrieval time records when this learning dataset was collected. Those times can differ by many years without contradiction.

For Tohoku, the stored origin is 2011-03-11T05:46:24.120Z, while the stored update is 2026-10-16T10:38:09.160Z. The latter is not another earthquake. It also does not tell you, by itself, which individual field changed. Determining that would require comparing record versions or associated revision information.

The final Z marks UTC. A local civil date depends on the time zone, so a UTC calendar date should not silently become a local date. Ridgecrest’s stored origin is 2019-07-06T03:19:53.040Z. Preserve that exact UTC timestamp when comparing it with another account; if an account gives a different local date, establish its time-zone convention before calling it an error.

The USGS GeoJSON format separates event time, update time, magnitude, magnitude type, status and identity fields. These distinctions are part of the evidence record, not decorative metadata. USGS description of the catalog summary format.

Preserve aliases and returned identities

The Tohoku request used the identifier usc0001xgp, but the returned canonical record identifier in this snapshot is official20110311054624120_30. Both are preserved. The request alias documents how the record was obtained; the returned identifier documents which record was supplied. Treating them as two independent earthquakes would double-count one event.

Compare this with Nepal’s us20002926 and Ridgecrest’s ci38457511, whose requested and returned identifiers agree here. The source links lead to the Tohoku record, Nepal record and Ridgecrest record. The local snapshot preserves the selected metadata used for the browser calculations rather than copying source imagery.

Read estimates as estimates

All three stored records have reviewed status. That status does not make their source parameters exact or permanently unrevisable. Magnitude, depth and location are interpreted estimates produced from observations and methods; the subset does not include the raw waveforms needed to independently reconstruct them.

The types mww and mw belong to the moment-magnitude family. In particular, mww denotes the W-phase method; it is not the local Richter magnitude ML. Preserve the supplied method label instead of replacing every magnitude with the familiar word Richter. USGS magnitude-method table.

A magnitude printed to one decimal place does not establish a scientific uncertainty interval of plus or minus 0.05. Display precision and uncertainty in the estimate are different. Likewise, additional digits in a coordinate or depth do not independently prove corresponding accuracy.

Transfer: audit a proposed conclusion

A report says, “This dataset contains three major earthquakes, so the world has about one major earthquake every few years. The Tohoku event happened again when its catalog record was updated.” Identify the two evidence failures and rewrite the claims.

Check the earthquake-catalog transfer

The three events were deliberately selected, so their dates and count cannot estimate global occurrence frequency. The update timestamp describes the record, not a new occurrence. A defensible report identifies the three selected events and the snapshot version, and distinguishes their origin times from later catalog updates.