What this explorer shows
The Earthquake Risk Explorer is an interactive map that pulls the public USGS earthquake catalogue into your browser and turns the past record into simple long-term statistics for any circle you choose on Earth. Pick a place by clicking the map, searching a city name, using your device location, a preset, or typing latitude and longitude, then set a radius in kilometres and a minimum magnitude. The page queries the USGS FDSN event API live (CORS is allowed), counts every earthquake of that size inside the circle since 1900, and summarises how often such events have occurred. It also overlays plate boundaries from the PB2002 model and, if you switch them on, a simplified copy of the GEM Global Active Faults database.
Statistical probabilities, not predictions
No model on this page — or anywhere else — can say that a quake of a certain size will strike a certain town on a certain day. What you see are long-term statistical probabilities from a time-independent Poisson model: if events of magnitude M or larger happened at an average rate of r per year in that circle, the chance of at least one in the next t years is 1 − e^(−r·t). That is a statement about average behaviour over decades, not a forecast of the next rupture. Real hazard also depends on which fault is loaded, how soft the soil is, and how buildings are built. Use the numbers for study and education; for safety follow your national seismic authority.
How the rate is estimated
Older catalogues miss smaller shocks, so the tool only starts the rate clock when the chosen magnitude is reasonably complete worldwide: from 1900 for M≥7, from 1964 for M≥6, and from 1973 for smaller thresholds. By default it then removes aftershocks with Gardner–Knopoff (1974) space–time windows so the remaining events are closer to independent mainshocks; you can turn that off with the checkbox. The annual rate is N divided by the years in that completeness window. If N is zero, the page refuses to print a false 0% and instead shows a 95% upper bound using the rule of three. The Gutenberg–Richter b-value is estimated with the Aki–Utsu maximum-likelihood formula (Mc = your minimum magnitude, ΔM = 0.1) when at least ten events are available. Only events with eventtype=earthquake are counted.
Live feeds, alerts, charts and sharing
Beside the analysis panel you will find a nearby list sorted by distance, optional in-tab browser notifications when a new quake above your chosen magnitude appears inside the radius while the tab stays open, canvas charts of events per year and a magnitude histogram, a heatmap-style density toggle, a dark map basemap, filters by magnitude, depth and year, an estimate of distance to the nearest plate boundary or loaded fault, and CSV or GeoJSON export. Shareable addresses use the form #lat,lon,radius,minmag. Map tiles come from OpenStreetMap; place search uses Nominatim and runs only when you press Search. Attribution for USGS ComCat, PB2002, GEM (CC BY-SA 4.0), OpenStreetMap and Nominatim is listed on the tool itself.