What is the Epicenter of an Earthquake?

Tiffany Leonard, David Wood
  • Author
    Tiffany Leonard

    Tiffany has worked on science curriculum and lesson writing since 2015. She has her Master's in Geology from the University of Illinois and a Bachelor's in Geology and Physics from Carleton College. She taught geology courses while she was getting her MS and was a TA while at Carleton.

  • Instructor
    David Wood

    David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

What is the epicenter of an earthquake? Learn the epicenter definition, where to find the epicenter of an earthquake, and why we need to find the epicenter. Updated: 10/02/2021

What is the Epicenter of an Earthquake?

An earthquake can be a major natural disaster, causing massive amounts of destruction in its wake. The epicenter of an earthquake is the surface expression of the earthquake. It is located directly above the focus or hypocenter of the earthquake, which is where the earthquake begins at depth. Earthquakes typically begin deep within the Earth's surface, with shallow earthquakes still located up to depths of 70 km. Most people are more aware of the epicenter than the hypocenter, as the epicenter is easier to plot on the map

The epicenter tends to be the point on the surface that experiences the most shaking. It is the first place the seismic waves hit on the surface after the initial rupture has occurred. However, this is not always the case. If the rupture of an earthquake is particularly large, the initial hypocenter location may be one of several hotspots where energy is released.

An example of an earthquake where shaking was more severe away from the epicenter is the 2002 Alaskan Earthquake. For that event, most of the damage occurred 330 km east from the epicenter, on the other end of the rupture.

The Hypocenter of an Earthquake

The hypocenter is the location where the earthquake begins deep within the Earth. When an earthquake begins, two sides of a fault move against each other and release pressure. A fault is a fracture zone between two blocks of rock (often two tectonic plates). Due to the fault, the blocks are allowed to move relative to each other. When the motion happens quickly, that is when an earthquake occurs. The hypocenter occurs where this motion or slip first begins.

The depth of the hypocenter determines how shallow or deep the earthquake is. Shallow earthquakes tend to be more destructive, because the energy is released much closer to the surface, causing more severe shaking.

Range of Earthquake Depths

Depth Range
Shallow Earthquakes 0 - 70 km
Intermediate Earthquakes 70 - 300 km
Deep Earthquakes Below 300 km

Despite the shallow range beginning at 0 km, earthquakes cannot occur at the surface of the Earth. Two blocks of rock must slide for an earthquake to be generated.

Differences between the Epicenter and Hypocenter

How can we differentiate between the epicenter and hypocenter? Both are locations that pinpoint earthquake activity. However, remember that epicenter is on the surface and the hypocenter is at depth.

Example from the 1989 Loma Prieta Quake

Latitude Longitude Depth
Hypocenter 37.04° N 121.88° W 19 km
Epicenter 37.04° N 121.88° W 0 km

The epicenter is located on the surface directly above the focus (hypocenter), which is located on the fault at depth.

Difference between an epicenter and a hypocenter.

The latitude and longitude will be the same for the epicenter and hypocenter of the same event.

What is an Epicenter?

Earthquakes can cause huge amounts of death and destruction. For this reason, understanding them is vitally important. Like all major events, seismic or otherwise, they have to start somewhere. The epicenter is the place on the Earth's surface under which they start.

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Locating the Epicenter of an Earthquake

Scientists use two different methods to determine the epicenter of an earthquake:

  1. Seismograph triangulation
  2. P- and S-Wave intervals

Often, these two methods will be combined to improve the overall accuracy of the location.

Seismograph Triangulation

Seismographs are instruments that scientists use to measure earthquake signals around the globe. They work by measuring the motion of the ground in the area they are installed. These instruments must be installed in the ground to get accurate readings. Seismographs are typically installed and operated as part of a network of instruments. Many seismographs must be used to get an accurate image of the earthquake.

The seismometer is the part inside the seismograph, often a pendulum or mass on a spring, that is used to measure the ground motion. However, people often use the terms seismometer and seismograph interchangeably.

Diagram of a simple seismograph. In this model, the seismometer is a pendulum. As the seismograph moves with ground motion, the seismometer will remain still, recording the motion on the paper roll.

Diagram of a seismograph

Triangulation Process

In order to use seismographs to locate the epicenter of a quake, at least 3 different instruments in different locations must be used.

Damage from an earthquake

Location of the Epicenter

There are two important locations in any earthquake. The most important is the hypocenter, or focus of the earthquake. This is the point where the earthquake truly begins, deep under the ground and located at a tectonic plate boundary, the border between two of the fragments the Earth's crust is broken into. It is where the plate boundary begins to rupture.

The epicenter on the other hand, is the point on the Earth's surface directly above the hypocenter. This is a more useful measure for human reporting because it can be shown on a map.

Features of an Epicenter

The epicenter is usually the location where the waves from an earthquake are most intense and, as a result, it is also the location with the most damage. But this isn't always true.

If an earthquake is particularly large, it may run across a large section of the plate boundary. In this case, the epicenter might only be one of many hotspot locations and damage could be greater elsewhere. In a 2002 Alaskan earthquake of magnitude 7.9, the greatest damage was 330 km away from the epicenter. The epicenter was at the western edge of the rupture, but more damage occurred at the eastern edge.

Locating an Epicenter

Scientists have come up with a number of ways to figure out the location of an epicenter. The simplest requires the positioning of seismographs, equipment that measure the strength of ground tremors and earthquakes, around the area. It is possible to use a process of triangulation to figure out the location of the earthquake.

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Video Transcript

What is an Epicenter?

Earthquakes can cause huge amounts of death and destruction. For this reason, understanding them is vitally important. Like all major events, seismic or otherwise, they have to start somewhere. The epicenter is the place on the Earth's surface under which they start.

Damage from an earthquake

Location of the Epicenter

There are two important locations in any earthquake. The most important is the hypocenter, or focus of the earthquake. This is the point where the earthquake truly begins, deep under the ground and located at a tectonic plate boundary, the border between two of the fragments the Earth's crust is broken into. It is where the plate boundary begins to rupture.

The epicenter on the other hand, is the point on the Earth's surface directly above the hypocenter. This is a more useful measure for human reporting because it can be shown on a map.

Features of an Epicenter

The epicenter is usually the location where the waves from an earthquake are most intense and, as a result, it is also the location with the most damage. But this isn't always true.

If an earthquake is particularly large, it may run across a large section of the plate boundary. In this case, the epicenter might only be one of many hotspot locations and damage could be greater elsewhere. In a 2002 Alaskan earthquake of magnitude 7.9, the greatest damage was 330 km away from the epicenter. The epicenter was at the western edge of the rupture, but more damage occurred at the eastern edge.

Locating an Epicenter

Scientists have come up with a number of ways to figure out the location of an epicenter. The simplest requires the positioning of seismographs, equipment that measure the strength of ground tremors and earthquakes, around the area. It is possible to use a process of triangulation to figure out the location of the earthquake.

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Frequently Asked Questions

What does epicenter mean?

The epicenter is the location on the Earth's surface that marks where the earthquake was initiated. It is not the actual location of the earthquake, but rather the superposition onto the surface.

What is an example of an epicenter?

An epicenter is typically the point on the Earth's surface where the most shaking and damage from an earthquake occur.

What are the focus and epicenter of an earthquake?

The focus or hypocenter is the location at the depth where the earthquake first ruptured. The epicenter is the point on the surface directly above the focus.

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