What causes earthquakes? - British Geological Survey (2023)

Earthquakes are the result of sudden movements along fault lines within the earth. The movement releases stored "elastic stress energy" in the form of seismic waves that propagate through the earth, shaking the ground surface. Such movement on faults is generally in response to long-term deformation and stress buildup.

The structure of the earth

Seismic waves from large earthquakes permeate the entire earth. These waves contain important information about the internal structure of the earth. As seismic waves pass through the earth, they are refracted, or bent, like light rays bending through a glass prism. Because the speed of seismic waves depends on density, we can use the travel time of seismic waves to map the change in density with depth and show that the earth is made up of layers.

This brittle outermost layer varies in thickness from about 25 to 70 km under the continents and from about 5 to 10 km under the oceans. The continental crust has a rather complex structure and is made up of many different types of rock.

Beneath the crust is the dense mantle, which extends to a depth of 2,890 km. It consists of dense silicate rock. Both P and S waves from earthquakes travel through the mantle, showing that it is solid.

However, there is separate evidence that parts of the mantle behave like a fluid over very long geologic time scales, with rocks slowly flowing in giant convection cells.

The boundary between the Earth's mantle and core lies at a depth of about 2,900 km. The core is iron and we know it exists because it refracts seismic waves and creates a "shadow zone" at distances between 103º and 143º. We also know that the outer part of the nucleus is liquid because S waves do not pass through it.

tectonic plates

The outermost layer of the earth has broken into about 15 large plates called tectonic plates. These plates form the lithosphere, which is made up of the crust (continental and oceanic) and the upper part of the mantle. The tectonic plates move very slowly relative to each other, usually a few centimeters per year, but this still causes enormous deformation at the plate boundaries, which in turn causes earthquakes.

Observations show that most earthquakes are associated with tectonic plate boundaries and plate tectonics theory can be used to provide a simplified explanation of the global distribution of earthquakes, while some of the properties of earthquakes Earthquakes can be explained by a simple elastic rebound theory.

What drives the movement of tectonic plates?

Beneath the tectonic plates is Earth's asthenosphere. The asthenosphere behaves like a liquid on very long time scales. There are a number of competing theories that try to explain what drives the movement of tectonic plates. Three of the forces that have been proposed as the main drivers of plate tectonic movement are:

  • Mantle Convection Currents: Warm mantle currents propel and transport lithospheric plates like a conveyor belt.
  • Ridge thrust (floating mantle at mid-ocean ridges): Newly formed plates at mid-ocean ridges are warm, so they have a higher elevation at the mid-ocean ridge than colder, denser plate material further out ; Gravity causes the top plate of the ridge to push the lithosphere further away from the ridge.
  • Plate pull: Older, cooler plates sink at subduction zones because, as they cool, they become denser than the underlying mantle, and the sinking colder plate drags the rest of the warmer plate behind her.

researchhas shown that the main driving force for most plate motions is plate traction, since plates with more subducted edges move faster. However, recent research also shows that ridge thrust is a force driving plate movement.

(Video) We are the British Geological Survey

Types of plate boundaries

There are three types of silver borders:

  • divergent: plates move apart
  • convergent: plates come together
  • transform: plates move next to each other

The boundaries between tectonic plates are formed by system faults. Each boundary type is associated with one of three basic fault types called normal, reverse, and strike faults.

The plates can move apart at a boundary. This type of limit is called a divergent limit. It is also known as a constructive plate boundary because new material is produced at the interface. This type of boundary is dominated by normal faults, although other types of faults can be observed.

What causes earthquakes? - British Geological Survey (13)

Hot magma rises from the mantle at mid-ocean ridges, pulling the plates apart. Earthquakes occur along the fractures that occur when the plates pull apart. Examples are the East African Rift Valley and mid-ocean ridges where two oceanic plates are pulling apart, such as the regions near the Azores and Iceland. Divergent boundaries are associated with volcanic activity, and earthquakes in these zones tend to be frequent and small.

Continental collisions create mountains and fold belts as rocks are pushed up. The plates can move towards each other in a limit. This type of boundary is called a convergent boundary and is dominated by thrust faults, although other types of faults can be observed.

What causes earthquakes? - British Geological Survey (14)

When the boundary is between an oceanic plate and a continental plate, it is also known as a destructive plate boundary. At subduction zones, the oceanic plate is pushed or subducted under the continental lithosphere. As the oceanic plate sinks, earthquakes are generated within the plate and at the interface between the plates.

Destructive plate boundaries include deep oceanic trenches, such as the Peru-Chile Trench, where the Nazca plate (an oceanic plate) is subducting beneath the South American (continental) plate, i.e., the oceanic plate is being pushed under of the continental plate. These limits tend to produce most earthquakes of magnitude greater than 6.0. Subduction zones also produce the strongest earthquakes.

Where the boundary between two continental plates is, one plate curves up over the other rather than one plate subducting. Examples are the Eurasian plate-African plate boundary forming the Alps and the Indian-Eurasian plate boundary forming the Himalayas where the Eurasian plate is being pushed up and over the Indian plate.

This type of boundary tends to create a diffuse zone of activity. Continental collisions create mountains and fold belts as rocks are pushed up.

What causes earthquakes? - British Geological Survey (15)

The plates can pass each other at a boundary in the same plane. This type of limit is called a transformation limit. This type of boundary is dominated by strike faults, although other types of faults can be observed.

When two plates slide past each other, shallow earthquakes occur. This type of plate boundary is also known as a conservative plate boundary because it includes movement but not loss or accumulation of material on the surface. Some examples are the San Andreas Fault in the US and the Anatolian Fault in Asia Minor.

What causes earthquakes? - British Geological Survey (16)

Transform boundaries often produce large, shallow-focused earthquakes. Although earthquakes occur in the central regions of the plates, large earthquakes do not usually occur in these regions.

elastic rebound theory

The elastic rebound theory was originally proposed by geologist Henry Fielding Reid after the Great San Francisco earthquake of 1906 to explain the deformation caused by earthquakes.

(Video) What Causes Earthquakes

Before an earthquake, the buildup of stress in the rocks on either side of a fault causes gradual deformation. Eventually, this deformation exceeds the frictional force holding the rocks together and sudden slippage along the fault occurs. This releases the built-up stress and the rocks on both sides of the fault return to their original shape (elastic rebound), but are displaced on both sides of the fault.

What causes earthquakes? - British Geological Survey (17)

types of errors

There are three basic types of errors: normal, reverse, and slippage. Certain types of faults are characteristic of different plate boundaries, although more than one type of fault often occurs there. This can help us understand the relative motion of the plates and the nature of the deformation.

For a normal error, the block above the error moves down relative to the block below the error. ©IRIS. All rights reserved.

With an inverted error, the block above the error moves up relative to the block below the error. ©IRIS. All rights reserved.

In strike slip, the movement of blocks along a fault is horizontal. ©IRIS. All rights reserved.

During an earthquake, the rock on one side of the fault suddenly slides relative to the other. The failure surface can be horizontal or vertical, or any angle in between. Faults are classified based on the fault angle with respect to the surface (known as dip) and the direction of slip along the fault.

Faults that move along the direction of the dip plane are called dip slip faults, while strike slip faults are classified as right-hand or left-hand. Faults that show both dip-slip and strike-slip motions are called slant-slip faults.

What causes earthquakes? - British Geological Survey (19)

(Video) Knowing about Earthquakes in the Mandatory Levant - Dr Sarah Irving

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What are the causes of earthquake in geology? ›

Earthquakes are usually caused when underground rock suddenly breaks and there is rapid motion along a fault. This sudden release of energy causes the seismic waves that make the ground shake.

What causes an earthquake GCSE geography? ›

Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get stuck. When this happens pressure builds up. When this pressure is eventually released, an earthquake tends to occur.

What causes earthquakes in the UK? ›

Earthquakes in the UK

They include regional compression caused by motion of the Earth's tectonic plates and uplift resulting from the melting of the ice sheets that covered many parts of Britain thousands of years ago. Each year, between 200 and 300 earthquakes are detected and located in the UK by BGS.

What are 3 major things that causes earthquakes? ›

Earthquakes are the result of sudden movement along faults within the Earth.
There are three types of plated boundary:
  • divergent: plates moving apart.
  • convergent: plates coming together.
  • transform: plates moving past each other.

What are the 10 main causes of earthquake? ›

Things that cause earthquakes
  • Groundwater extraction – decrease in pore pressure.
  • Groundwater – increase in pore pressure.
  • Heavy rain.
  • Pore fluid flow.
  • High CO2 pressure.
  • Building dams.
  • Earthquakes.
  • No earthquakes (Seismic quiescence)
4 Dec 2012

How are earthquakes caused geography? ›

The surface of the Earth is made up of tectonic plates that lie beneath both the land and oceans of our planet. The movements of these plates can build mountains or cause volcanoes to erupt. The clash of these plates can also cause violent earthquakes, where Earth's surface shakes.

What plate boundary causes earthquakes? ›

About 80% of earthquakes occur where plates are pushed together, called convergent boundaries. Another form of convergent boundary is a collision where two continental plates meet head-on.

What are the factors of earthquake? ›

Earthquakes are caused by the sudden release of energy within some limited region of the rocks of the Earth. The energy can be released by elastic strain, gravity, chemical reactions, or even the motion of massive bodies.

Why does the UK rarely get any earthquakes? ›

Because of its complex tectonic history, the crust of the UK south of the Iapetus Suture, the boundary between “Geological England” and “Geological Scotland”, is mostly rather weak and can rarely store sufficient energy for large seismic events; we consider a tectonic event with a magnitude 6 a VERY significant event ...

Is the UK on a fault line? ›

The geology of much of the UK is pretty old – hundreds of millions of years across much of the west of mainland Britain – and it is riddled with ancient fault lines that were once very active but are now virtually extinct.

Why doesn't the UK have earthquakes? ›

Most earthquakes happen at the boundaries between the Earth's tectonic plates, where there is the largest amount of stress. The UK is located in the middle of the Eurasian tectonic plate, so is not subject to significant earthquake activity.

What are the 3 most common stresses that cause earthquakes? ›

There are three types of stress: tensional, compressional, and shear. Tensional stress involves forces pulling in opposite directions, which results in strain that stretches and thins rock. Compressional stress involves forces pushing together, and compressional strain shows up as rock folding and thickening.

What is the direct cause of most earthquakes? ›

Most earthquakes are caused by the release of stresses accumulated as a result of the rupture of rocks along opposing fault planes in the Earth's outer crust. These fault planes are typically found along borders of the Earth's 10 tectonic plates.

What are the 5 main effects of earthquakes? ›

Earthquakes can result in the ground shaking, soil liquefaction, landslides, fissures, avalanches, fires and tsunamis.

How convergent boundaries cause earthquakes? ›

Earthquakes at convergent plate boundaries mark the location of the subducting lithosphere. The motion of the lithosphere as it plunges through the mantle causes the quakes. At greater depths, the plate heats up enough to deform plastically.

Do earthquakes occur at all plate boundaries? ›

Earthquakes occur along all types of plate boundaries: subduction zones, transform faults, and spreading centers. However, there are earthquakes which occur within plates.

What are the causes and measures of earthquake? ›

What Causes an Earthquake? Earthquakes are caused due to sudden tectonic movements in the earth's crust. When the tectonic plates slide over one another, there is a cause of orogeny which results in earthquakes and volcanoes. These disturbances cause vibrations that spread in all directions.

What stress causes earthquakes? ›

Faults are usually locked in the upper crust (right figure), leading to a gradual change in surface velocity across the fault and bending of the upper crust. This bending produces stress buildup that eventually leads to earthquakes.

Why does the UK not have volcanoes or strong earthquakes? ›

As Britain lies a long way from the plate boundaries, we have no volcanic activity. Plates move very slowly (a few centimetres per year) and so it will take millions of years before Britain will be 'at' a plate boundary. Consequently, we shall not need to worry about volcanoes for quite a long time to come!

Has UK ever had a major earthquake? ›

The North Sea earthquake of 7 June 1931, with a magnitude of 6.1ML and with an epicentre offshore in the Dogger Bank area (120 km NE of Great Yarmouth), is the largest known earthquake in the UK.

Why does Britain have no active volcanoes or major earthquakes? ›

There are no active volcanoes or major earthquakes in Britain because it is far away from areas that are seismically active. Those areas that are active are usually near the boundaries of tectonic plates.

Is the UK on its own tectonic plate? ›

Although the UK is not located on a plate margin and is therefore not currently tectonically active, this has not always been the case.

Could a tsunami hit UK? ›

The threat the UK faces from tsunamis is minimal. The British Isles sits in the middle of the tectonic plate known as Eurasia. The nearest plate boundary is at the mid-Atlantic ridge, where the earthquakes are too small to generate tsunamis.

Is the UK seismically active? ›

The maps confirm that seismic hazard is generally low in the UK but that the hazard is slightly higher in areas like Wales and north central England. This largely reflects the higher rates of historical earthquake activity in these regions.

When was the last major earthquake in the UK? ›

Earthquakes in the United Kingdom since 1950

The strongest earthquake in the United Kingdom happened on 09/22/2002 in the Mansfield, Dudley region with a magnitude of 4.8 on the Richter scale.

Is England prone to earthquakes? ›

YES, between 200 and 300 earthquakes are detected and located in the UK, by the British Geological Survey annually.

When was UK's last earthquake? ›

Magnitudes are local magnitude (ML) and are calculated to one decimal place, as is standard practice in earthquake seismology.
Last updated: Sat, 03 Dec 2022 04:00:01 (UTC)
Time (UTC)21:10:49.3
22 more columns

What type of fault causes the most earthquakes? ›

Reverse faults, particularly those along convergent plate boundaries are associated with the most powerful earthquakes, megathrust earthquakes, including almost all of those of magnitude 8 or more.

What 3 factors contribute to the amount of damage and shaking during an earthquake? ›

Many factors influence the strength of earthquake shaking at a site including the earthquake's magnitude, the site's proximity to the fault, the local geology, and the soil type.

Does human activity cause earthquakes? ›

The three main reasons are wastewater injection, hydraulic fracturing and enhanced oil recovery. Within the United States, each of these three activities has induced earthquakes to varying degrees in the past few years.

What is earthquake in geology? ›

An earthquake is what happens when two blocks of the earth suddenly slip past one another. The surface where they slip is called the fault or fault plane.

What causes fault in geology? ›

A fault is formed in the Earth's crust as a brittle response to stress. Generally, the movement of the tectonic plates provides the stress, and rocks at the surface break in response to this.

What are the 4 types of earthquake? ›

There are four different types of earthquakes: tectonic, volcanic, collapse and explosion. A tectonic earthquake is one that occurs when the earth's crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes.

What is earthquake and how its start? ›

An earthquake is a weak to violent shaking of the ground produced by the sudden movement of rock materials below the earth's surface. The earthquakes originate in tectonic plate boundary.

What are the 4 major faults? ›

There are four types of faulting -- normal, reverse, strike-slip, and oblique. A normal fault is one in which the rocks above the fault plane, or hanging wall, move down relative to the rocks below the fault plane, or footwall. A reverse fault is one in which the hanging wall moves up relative to the footwall.

What are the three types of faults geology? ›

There are three main types of fault which can cause earthquakes: normal, reverse (thrust) and strike-slip.


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