How these numbers are produced
Every earthquake on this site comes from the United States Geological Survey Earthquake Hazards Program, retrieved through its public FDSN event web service. Nothing is estimated, interpolated or averaged between sources. Where USGS has not published a value, this site says so rather than filling the gap.
The source, and how often it updates
USGS publishes located earthquakes through the FDSN event service, an international standard interface also used by other national seismic networks. It is public domain US federal government work, free to use and requiring no account.
Every place page on this site is rebuilt from that service, and the table on each page then refreshes itself in your browser directly from USGS when you load it. The date and time stamped at the top of each table tells you which of the two you are reading.
Magnitudes for recent events are revised. An automatic solution is published within minutes and a reviewed one usually replaces it within a day, sometimes shifting the magnitude by a few tenths. A number here that disagrees slightly with a news report is usually this, and USGS is the one to trust.
The magnitude floor, and why counts are not comparable
Counting "all earthquakes" in a region is not as simple as it sounds, because how small an earthquake can be detected depends on how many seismometers are nearby. California is densely instrumented and records events below magnitude 1 routinely; a sparsely monitored region of the same size might only catch magnitude 3 and above. Comparing raw counts between the two measures instrumentation, not seismicity.
So every place page states the magnitude floor its counts were taken at, and pages do not compare their totals with each other. A place that reports fewer earthquakes than another is not necessarily quieter.
The service also refuses any query matching more than 20,000 events rather than silently returning a truncated list. Where a region would exceed that, the floor is raised until the query is answerable, and the page reports the floor that produced its numbers.
What "in and around" means
State and country pages are built from a latitude and longitude rectangle covering the region. No state is a rectangle, so the box necessarily includes some ground outside the border, and an event a few kilometres into a neighbouring state can appear on the list. That is why those pages say "in and around" and why every row shows the location text USGS itself published, which names the nearest town.
City pages are different: they use a circular search around the city centre, so "within 100 km of Los Angeles" is exactly what it says. The radius is stated on each page.
Why does this site show a different number of earthquakes than another one?
- Almost always the magnitude floor or the search area. A site counting everything above magnitude 1 in a box drawn slightly differently will report a different total for the same region and the same week. Both can be correct. This is why every page here states its floor and its area.
Is USGS earthquake data free to use?
- Yes. It is work of the United States federal government and carries no copyright in the US. USGS asks that you credit it, which this site does on every page.