Earthquake Depth Explained: Why It Matters

By Quake Tracker Live Editorial · Published November 9, 2026

Every earthquake listing has a depth next to the magnitude, and it is easy to skip. It should not be skipped. Depth tells you how far below the surface the rupture began, and it helps explain why two earthquakes of the same magnitude can feel completely different, and why some strong quakes cause almost no damage while others devastate a city.

What "depth" means

An earthquake starts at a point underground called the hypocenter (or focus). The point on the surface directly above it is the epicenter, which is the location you see on maps. Depth is the distance between the two, normally given in kilometers below the surface. On our earthquake pages the depth is shown in both kilometers and miles.

The rupture of a large earthquake is not a point. A magnitude 7 fault can slip over a patch tens of kilometers long, and the slip spreads out from the hypocenter. The depth is where it began, and the shaking you feel comes from the whole patch.

Shallow, intermediate and deep

The USGS groups earthquakes by depth into three classes:

The majority of earthquakes, and nearly all of the damaging ones, are shallow. The large majority of the earth's seismic energy release comes from shallow events. Deep earthquakes are rarer and are found almost exclusively along subduction zones, such as around Japan, the Philippines, Tonga and South America.

Why depth changes the shaking

Seismic waves lose strength as they spread out and travel through rock. If everything else is equal, the closer you are to the source, the stronger the shaking. A shallow earthquake puts the source close to the surface, so people near the epicenter feel the full force, and a smaller earthquake can cause serious damage. A deep earthquake puts the source hundreds of kilometers away, so the waves spread out over a much larger area and arrive weaker.

This produces a pattern that surprises people:

• A shallow M6 under a city can cause more damage than a deep M7 hundreds of kilometers underneath it.
• Deep earthquakes are usually felt over a wider area but with lower intensity.
• Deep earthquakes seldom produce large tsunamis, because they do not displace the sea floor much. A shallow offshore thrust earthquake is what typically does that.
• There are exceptions. Strong earthquakes inside a descending plate can be very damaging when they are close to cities. The 2017 Puebla earthquake in Mexico (M7.1, about 48 km deep, still in the shallow class) killed hundreds of people in Mexico City and nearby states, partly because the soft lake-bed soils under the capital amplify shaking.

Why earthquakes occur at different depths

In the cold, brittle upper crust, rocks build up elastic strain and then snap along faults. That explains shallow earthquakes. Deeper, rocks get hotter and flow more easily, which is why in most places earthquakes stop below roughly 15 to 25 km. California's San Andreas system, for example, is mostly shallow.

Subduction zones are the exception. When an oceanic plate dives into the mantle, it carries cold rock with it, and that cold slab stays brittle enough to break at far greater depths. Intermediate and deep earthquakes outline the slab like a map of its descent, which is how seismologists first discovered subduction in the mid-20th century. At depths beyond 300 km, the pressure is so high that ordinary friction-based faulting should not work. Researchers believe that mineral transformations inside the sinking slab, in which minerals collapse into denser forms, play a role. It remains an active area of research.

How accurate is the depth number?

Depth is usually the least certain part of an earthquake report. Latitude and longitude can often be pinned down to a few kilometers, but depth depends on how many seismographs are close to the epicenter, and how well the speed of seismic waves through the local rock is known. For an offshore quake with stations only on distant coasts, the depth can be uncertain by tens of kilometers.

Some things to know when reading a depth:

• Fixed depths. When the data cannot resolve depth, agencies fix it at a default, often 10 km, and sometimes 33 km. If you see exactly 10.0 km on an earthquake page, the number may be a placeholder, not a measurement.
• Revisions. Depth is often updated during the hours after the event as analysts add stations and use depth phases, which are reflections from the surface that reveal how deep the source was.
• Differences between agencies. The USGS, EMSC and GEOFON can report different depths for the same event, particularly in the first hour. We label preliminary solutions on the earthquake pages.

Depth and what you feel

Depth affects the character of the shaking as well as its strength. Shallow earthquakes close to you tend to produce a sudden jolt and sharp, high-frequency shaking, often with a loud bang. Deeper or more distant events tend to feel like a rolling or swaying motion, slower and longer. Tall buildings respond more to the long-period waves of large, distant earthquakes, which is why people on upper floors can feel an event that people on the ground barely notice.

Checking depth on our site

Every earthquake page on Quake Tracker Live lists depth with the magnitude, and the map markers show it as well. To compare places, look at the zone pages for California, Alaska or Japan. You will see that California events cluster at shallow depths, while Japan has many more intermediate and deep events from its subduction zones. For help with how to interpret a magnitude, read our magnitude scale guide.

Frequently asked questions

Sources and further reading

• USGS: Earthquake hazards
• USGS Earthquake Catalog (ComCat)

This guide is general information, not professional or emergency advice. Quake Tracker Live is not an official warning system; follow instructions from local authorities.