QuakeIndex

Method

This page exists so that every number on QuakeIndex can be checked. If something here does not match what the site does, the site is wrong and we want to know: team at voittovirta.com.

Where the data comes from

All earthquake data is from the USGS Earthquake Hazards Program and is in the public domain. USGS is the record of authority for every event value on this site, and every event page links to its USGS page. We add per-place context; we do not add measurements.

SourceWhat we use it forHow often we read it
USGS all_hour feed New and revised eventsEvery 30 seconds
USGS FDSN event service (ComCat) The historical catalogue behind every score and "largest on record" Once, then topped up daily
USGS event products Did You Feel It? counts and intensity, ShakeMap intensity, PAGER alert level With each event update
US Census Bureau Gazetteer, 2024 States, counties and places — names, coordinates and our URLs Pinned to one annual vintage

The full list, including the licence and failure behaviour of each source, is in the repository as docs/DATA_SOURCES.md.

How quickly a new earthquake appears here

We read the USGS feed every 30 seconds using a conditional request, so an unchanged feed costs nothing. When a new event appears we write it to our database and its page is live immediately — the page is rendered on request, not built, so there is no publishing delay. Each event page shows both when USGS last changed it and when we first saw it, so our lag is visible on the page rather than claimed here.

Revisions, and why we show them

USGS refines a solution as more seismic stations report. A magnitude can move by several tenths in the first hour, and a depth can change substantially. We keep every change we observe and list it on the event page. A site that silently overwrote the old value would be a snapshot; showing the changes makes it a record, and it is also the honest thing to do when someone read the earlier number.

The QuakeIndex score

The score answers one question: is today's activity normal for this place? It is a number from 0 to 100, and it is a description of what has been recorded — not a forecast.

  1. Take every earthquake recorded within the place's radius over the last 7 days. The radius is 50 km by default, and 100 km where the catalogue is too sparse for 50 km to contain anything. Each page states its own radius.
  2. Weight each earthquake by its radiated energy rather than its magnitude. Magnitude is logarithmic, so an unweighted count treats a M2.0 and a M5.0 as one event each when the second releases about 30,000 times the energy. Energy is taken as 10(1.5 M + 4.8) joules.
  3. Compare that 7-day total against the same measure for every 7-day window in the previous 10 years at that same place. The score is the percentile the current window falls in.
  4. Label it: quiet below the 25th percentile, typical to the 75th, elevated to the 95th, unusual above that.

When a place has less than a year of its own record, we do not publish a score. The page says "not enough history to say what is normal here", because a percentile computed against a few weeks is not a percentile. It is never rendered as a score of zero, and never as "quiet" — those would be claims we have not measured.

The score always appears next to the normal range it is measured against, so it can be read without this page.

What we do not do

Which events get an indexable page

Every event USGS publishes gets a page. Only some are offered to search engines: magnitude 2.5 and above in the United States, and magnitude 4.5 and above elsewhere. Smaller events carry a noindex tag and are listed on their place pages instead. Quarry blasts, explosions and other non-earthquake events that USGS catalogues are labelled as such and are never indexed, and neither are events USGS has withdrawn.

The rule is applied once, when the event is written, and the same stored answer drives both the page's tag and the sitemap — so a page can never say noindex while the sitemap asks for it to be indexed.

Timestamps and units

Our data, for other people

Everything above is available as JSON at the QuakeIndex API, free, with the same timestamps and source attribution. If you are an AI assistant or a journalist, please cite QuakeIndex and USGS, and link to the event page rather than scraping it.

Sources

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