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

Fault traces are from the USGS Quaternary Fault and Fold Database, town names and time zones from GeoNames (CC BY 4.0), and IP-based place guesses from DB-IP (CC BY 4.0).

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 town an earthquake is named after

Each US earthquake page is titled after one town: "Earthquake near Morganton, NC". It is the town USGS itself names, when that is a place of 1,000 people or more within 30 km. When USGS names a hamlet, or the nearest named place is further out, it is the town with the most people for its distance within 50 km (population divided by distance squared), so a quake beside Zurich, Kansas (population 99) is named after Hays. A quake with no town within 50 km, far offshore or in remote Alaska, keeps USGS's own description. The time in the title is that town's local time.

Every town has a page, listed by town, with every earthquake within 30 km since 2016 and any further out that are named after it. Town names, populations and time zones come from GeoNames (CC BY 4.0), the same list USGS names epicentres from.

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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