Frequently Asked Questions

The map and the data

Is this a live earthquake map?

No. This is a historical archive of magnitude 4.5+ earthquakes since 1900, refreshed from the USGS catalogue from time to time. For real-time information, use the USGS Latest Earthquakes map, the European-Mediterranean Seismological Centre, or your national agency.

Where does the data come from?

The USGS Earthquake Catalog, compiled by the U.S. Geological Survey from seismic networks worldwide. It is public-domain data. See the about page for how it is processed.

Why does the map start at magnitude 4.5?

Below magnitude 4.5, the historical global catalogue is incomplete and biased toward regions with dense seismic networks, so a lower threshold would misrepresent where earthquakes actually happen. At 4.5 and above the modern record is close to globally complete.

Why are there so few earthquakes before about 1960?

There were fewer and less sensitive seismometers, and huge areas — the oceans, the Southern Hemisphere, Antarctica — had almost no coverage. Only the largest earthquakes were detected and located. Global completeness for magnitude 4.5+ dates from roughly the 1970s.

Why do the earthquakes form narrow lines?

Those lines are the boundaries between tectonic plates, where almost all of the stress that causes earthquakes is concentrated. See Plate Tectonics and Earthquakes for the full explanation.

What do the colours and circle sizes mean?

Colour shows focal depth — red and orange are shallow (0–70 km), yellow intermediate, blue and violet deep (150 km and below). Circle size scales with magnitude on a curve, because the magnitude scale is logarithmic and a linear size would make large earthquakes invisibly small next to the difference in energy they represent.

Earthquake science

What is the difference between the Richter scale and moment magnitude?

The Richter (local magnitude) scale was calibrated for moderate earthquakes on one instrument in southern California and undercounts very large earthquakes. Moment magnitude is based on the physical size of the fault rupture and works across the whole range. Modern reported magnitudes are moment magnitude even when the media call them “Richter.” See Earthquake Magnitude Scales.

How much bigger is a magnitude 7 than a magnitude 6?

About 10 times more ground-shaking amplitude on a seismograph, and about 32 times more energy released. A magnitude 8 releases about 1,000 times the energy of a magnitude 6.

What was the largest earthquake ever recorded?

The magnitude 9.5 earthquake near Valdivia, Chile, on 22 May 1960 — the largest since instrumental recording began, according to the USGS. The largest earthquakes page has the full top-20 list.

Why don’t earthquakes happen below about 700 km?

Deeper than roughly 700 km, mantle rock is hot enough to deform by slowly flowing rather than by suddenly fracturing, so the stored elastic stress needed for a sudden slip cannot build up. The deepest earthquakes, in the 300–700 km range, occur inside cold slabs of subducted ocean floor.

Can earthquakes be predicted?

No. Neither the USGS nor any other scientific body can predict the date, time, place and magnitude of a specific future earthquake, and no reliable method exists. Scientists can estimate the long-term probability of an earthquake in a region, and can issue aftershock forecasts after a large earthquake. Earthquake early warning systems are different: they detect a quake that has already started and send an alert a few seconds ahead of the shaking.

Do small earthquakes prevent big ones?

Not meaningfully. Because the energy scale is logarithmic, it would take roughly 32 magnitude 6 earthquakes, or about 1,000 magnitude 5s, to release the energy of a single magnitude 7. The steady background of small earthquakes barely dents the stress that drives a large one.

Are earthquakes becoming more frequent?

The long-term global rate of large earthquakes (magnitude 7 and above) has been roughly steady. What has increased is the number of seismometers and the speed of reporting, so more small earthquakes are detected and news of any given event spreads faster. Human activities such as wastewater injection have raised local rates in a few specific regions.

Safety

Where can I get earthquake alerts and safety information?

For alerts, follow your national geological survey or civil-protection agency; in the United States the USGS operates the ShakeAlert early-warning system on the West Coast. For what to do during shaking, the standard guidance is Drop, Cover and Hold On — see your national preparedness agency (for example ready.gov, or the equivalent in your country). This website is an educational archive and is not a source of emergency information.