Earthquakes on the Map

What Is an Earthquake?

An earthquake is the shaking of the ground caused by a sudden release of energy in the Earth’s outer layers. Almost all of that energy comes from rock breaking and sliding along a fault — a fracture in the crust where two blocks move past each other. Stress builds up slowly as tectonic plates grind against one another, and when the friction holding the fault finally gives way, the rock slips in seconds. The energy radiates outward as seismic waves, which is what we feel as shaking (U.S. Geological Survey).

The point underground where the slip begins is the hypocenter (or focus); the spot on the surface directly above it is the epicenter. The map above plots epicenters. Every coloured dot is one recorded earthquake, positioned where the USGS located its epicenter and coloured by how deep below the surface the rupture started.

Where Earthquakes Happen

Earthquakes are not scattered at random. Set the map to “everything up to here” and the dots trace a set of narrow lines that wrap around the globe — these are the boundaries between Earth’s tectonic plates. Roughly 90% of the world’s earthquakes, and most of the largest ones, occur around the rim of the Pacific Ocean in the belt known as the Ring of Fire (U.S. Geological Survey).

The other major belts are easy to pick out: the Alpide belt running from the Mediterranean through the Himalayas to Indonesia, and the mid-ocean ridges, a continuous underwater mountain range where new sea floor is created and plates pull apart. Where two plates collide and one dives beneath the other — a subduction zone — the largest earthquakes on the planet are generated.

A minority of earthquakes strike far from any plate boundary. These intraplate earthquakes are rarer but can still be destructive: the 1811–1812 New Madrid sequence in the central United States and the 2001 Bhuj earthquake in India are well-known examples.

Shallow and Deep Earthquakes

Earthquakes are classified by the depth of their hypocenter. Shallow earthquakes (0–70 km) account for about three-quarters of the total energy released worldwide and cause the great majority of damage, because the shaking has less rock to travel through before it reaches the surface. Intermediate (70–300 km) and deep (300–700 km) earthquakes occur almost exclusively inside slabs of old ocean floor that have subducted into the mantle (U.S. Geological Survey).

No earthquake has ever been reliably recorded from deeper than about 700 km. Below that, the rock is hot enough to deform by flowing rather than by brittle fracture, so stress cannot build up to the point of a sudden slip. On the map, deep earthquakes appear in blue and violet and cluster behind subduction zones — inland of the trench, on the side the sea floor is sinking toward.

How the Size of an Earthquake Is Measured

The number attached to an earthquake is its magnitude — a measure of the energy released at the source. The original Richter scale (local magnitude, M_L), devised by Charles Richter in 1935, works well for moderate earthquakes in southern California but saturates for large ones. Since the 1970s seismologists have used moment magnitude (M_w), which is calculated from the physical size of the fault rupture and does not saturate (Hanks & Kanamori, 1979). News reports still often say “Richter,” but the figure is almost always moment magnitude.

The scale is logarithmic. Each whole step up multiplies the ground-motion amplitude recorded on a seismograph by about 10, and the energy released by about 32. A magnitude 7 earthquake therefore releases roughly 1,000 times the energy of a magnitude 5, and about a million times that of a magnitude 3.

Magnitude describes the earthquake at its source. How strongly the ground actually shakes at a given place — which depends on distance, depth, and local soil — is described separately by intensity, reported on the twelve-level Modified Mercalli scale (I, barely detectable, to XII, total destruction).

How to Read This Map

Each circle is one earthquake. The controls let you filter and move through time:

• Colour shows focal depth: red and orange are shallow (0–70 km), yellow is intermediate, blue and violet are deep (150 km and below).
• Size scales with magnitude. Because the scale is logarithmic, a magnitude 8 circle is drawn far larger than a magnitude 5 — that reflects a real difference of thousands of times more energy.
• The year slider moves through the record one year at a time. Press Play to sweep from 1900 to today.
• Show switches between a single year, a rolling 5-year window, a full decade, or the entire record accumulated up to the selected year.
• Min magnitude hides smaller events so the pattern of the largest earthquakes stands out.

A note on the early years: instrument coverage before about 1960 was sparse, especially in the Southern Hemisphere and the open oceans, so early decades under-count real activity and are biased toward large, well-recorded shocks. The pattern becomes globally reliable from roughly the 1970s, when the World-Wide Standardized Seismograph Network came into full operation.

Some Earthquakes in the Record

Dragging the slider to the right years brings up events that shaped modern seismology. All magnitudes below are the USGS moment-magnitude values:

• 1960 — Valdivia, Chile (M9.5): the largest earthquake ever instrumentally recorded. It ruptured about 1,000 km of the plate boundary and generated a Pacific-wide tsunami.
• 1964 — Prince William Sound, Alaska (M9.2): the largest recorded in North America. Its aftershock cloud is clearly visible on the map for that year.
• 2004 — Sumatra–Andaman (M9.1): the rupture ran for roughly 1,300 km; the tsunami killed about 228,000 people around the Indian Ocean.
• 2011 — Tōhoku, Japan (M9.1): the offshore rupture and tsunami caused the Fukushima nuclear accident; the year’s dense aftershock sequence off northeast Japan stands out on the map.
• 1976 — Tangshan, China (M7.6): a shallow earthquake directly beneath a city; official figures record 242,000 deaths, one of the deadliest of the 20th century.

About the Data

Every earthquake on this map comes from the USGS Earthquake Catalog, delivered through the FDSN Event Web Service. It is compiled by the U.S. Geological Survey’s National Earthquake Information Center from thousands of seismic stations worldwide, and it is in the public domain.

We include every event of magnitude 4.5 or greater from 1900 to the present. That threshold is deliberate: below about magnitude 4.5 the historical global catalog is incomplete and heavily weighted toward well-instrumented regions such as California and Japan, so a lower cut-off would make some countries look far more seismically active than they are simply because they have more seismometers. At magnitude 4.5 and above, the modern catalog is close to globally complete.

The USGS locates roughly 20,000 earthquakes a year — about 55 a day — and estimates that several million occur annually, most too small to be felt. On the scale of the largest events, a magnitude 8 or greater earthquake happens about once a year on average worldwide.

Frequently Asked Questions

Does this map show earthquakes happening right now?

No. It is a historical archive that is refreshed periodically, not a live feed. For real-time information see the USGS “Latest Earthquakes” map or your national seismological agency.

Why do the earthquakes form lines instead of covering the whole map?

The lines are the boundaries between tectonic plates. That is where almost all of the stress that drives earthquakes is concentrated, because that is where plates are pushing, pulling, or grinding past each other. The interiors of plates are comparatively quiet.

Why are there so few earthquakes before 1960?

Seismometers were fewer and less sensitive, and large regions — 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.

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

The Richter (local magnitude) scale was calibrated for moderate earthquakes recorded on a specific 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.”

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. It is on the map in the 1960 view, off the coast of central Chile.

Can earthquakes be predicted?

No. Neither the USGS nor any other scientific organization can predict the date, time, location, and magnitude of a specific future earthquake, and no reliable method exists. Scientists can, however, calculate long-term probabilities for a region and issue short-term aftershock forecasts.