Methodology

What Namazu publishes

Namazu publishes earthquake probabilities for the Pacific Ring of Fire and the Caribbean. Each number says how likely it is that at least one earthquake of a certain magnitude happens in a region within a time window.

Namazu doesn't guess, it measures: each forecast is sealed before its window passes and is then compared with what happened.

In the live list, an earthquake inside a region carries the region's name. One outside the regions carries the name of the country where it happened, "off the coast of" the nearest country if it happened at sea near its coast, or the name of the sea or ocean, with the mark that it has no Namazu forecast below it. Those names are from Natural Earth (at 1:50m scale), in the public domain, and they express no position of Namazu on sovereignty or borders: where Natural Earth marks a territory as disputed, the earthquake is shown without a name. The map's coastline is at another scale (1:110m), so near the coast a point may look like it is on land and be named by the sea, or the other way around.

How to read a probability

A probability is not a countdown. A 10% chance in one week means that, over many weeks with similar conditions, at least one such earthquake would be expected in one week out of ten.

Each statement comes with its reference rate. For a region, it is its usual probability; after an earthquake, it is the average rate at which an earthquake like that is followed by a larger one. Comparing the probability with that rate tells you whether it is above or below normal.

When the window of a statement ends, it is no longer shown and the one that replaces it appears.

Your region's large figure is its usual probability, for the magnitude and period its label states. If a recent earthquake raised the probability of a larger one above the average, the large figure becomes that one, as calculated at the time of the earthquake, with the average next to it. The list of regions gives each one's usual probability: regions differ in size and are not compared with one another.

After an earthquake, Namazu calculates the probability that a larger one follows nearby. If it is above the average after an earthquake like that, the region appears in "What moved this week", with how many times it exceeds the average. If a region has several recent earthquakes, the largest of those above the average is described.

A region's usual probability includes aftershocks in its long-run average, but does not rise when a recent large earthquake leaves a sequence under way. Namazu has a hypothesis that does take that sequence into account (the aftershock tail): it passed its evaluation on historical data and is now being validated live, week by week, under a rule sealed before it started. While that validation is under way, we show it on its region's page as our hypothesis under evaluation, next to the usual probability and never in its place; if it fails its validation, it is no longer shown.

Aftershocks and maps

After an earthquake, Namazu calculates the probability of a larger one nearby, with the radius and period each statement gives; it does not yet calculate the probability of aftershocks of any size. After a large earthquake, it also draws the area where aftershocks are expected. The map's colors are relative to that same map: they are not figures, they are not compared across maps and they do not tell you what to do. The coastlines on the maps are from Natural Earth, in the public domain. The typeface is IBM Plex, under the free SIL OFL license.

Each map is evaluated when its window closes, first preliminarily and then in final form. The results of those evaluations are published on each region's page.

What Namazu is not

Namazu does not tell anyone what to do and does not replace civil protection authorities. To know what to do, look to the authorities of your country; each region's page links to them when their site is verified.

Times

The time of an earthquake is shown in 24-hour format in the time zone of the place where it happened, with its offset from UTC; at sea, in nautical time. If your time zone has a different offset, you also see your own time.

Bulletins

Each region has citable bulletins: fixed texts with their id, which do not change after they are issued. Each bulletin's page says whether it is still current, whether there is a more recent one or whether it was annulled and why.

Your data

Your location is used only on your device to suggest a region: it is never sent to any server.

The website keeps two preferences in your browser: the language, and the region only if you choose it yourself.

The server's technical logs include the IP address of each visit and are deleted after 30 days.