A volcano tectonic earthquake or volcano earthquake is caused by the movement of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

beneath the surface of the Earth. The movement results in pressure changes where the rock around the magma has a change in stress. At some point, this stress can cause the rock to break or move. This

seismic activity An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...

is used by scientists to monitor volcanoes. The earthquakes may also be related to dike

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

and/or occur as

earthquake swarm In seismology, an earthquake swarm is a sequence of seismic events occurring in a local area within a relatively short period. The time span used to define a swarm varies, but may be days, months, or years. Such an energy release is different fr ...

s. Usually they are characterised by high seismic frequency and lack the pattern of a main shock followed by a decaying aftershock distribution of fault related tectonic earthquakes.

Cause of volcano tectonic earthquakes

One possible scenario resulting in a possible volcano tectonic earthquake occurs in tectonic subduction zones. The compression of plates at these subduction zones forces the magma beneath them to move. Magma can not move through the newly compressed crust as easily. This means it tends to pool in

magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it u ...

s beneath the surface and between the converging tectonic plates. Many of the famous and most well known volcanoes are of this type, including those of the

Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a tectonic belt of volcanoes and earthquakes. It is about long and up to about wide, and surrounds most of the Pa ...

. As the plates move, magma underground may be forced in and out of these chambers and form intrusions into surrounding crust. This movement is capable of causing the unstable rocks around it to cave in or shift. The movement of this magma as described, causes measurable seismic activity. Where plates diverge such as at

mid-ocean ridge A mid-ocean ridge (MOR) is a undersea mountain range, seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading ...

s the magma also can move into storage chambers and form intrusions again causing shifts in the rocks around them that can be detected as earthquakes. This is separate from earthquakes directly related to faults. However it is known than tectonic earthquake triggering has occurred with some volcanic eruptions, and there may be other associations of these in place and time with some eruptions, which could cause confusion because of the similar terminology. Scientists monitoring volcanoes have noticed that magma movement may lead to earthquake swarms depending on the movement of magma and the interaction with rock beneath the ground. Additionally, the volatility of volcanoes and the accompanying earthquakes has been shown to be linked to dike induced stress and the interaction this causes between the magma, rock, and wall of the chamber.

Importance

Volcano tectonic

seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 194 ...

is an important tool as it may predict the eruptions of volcanoes. Seismic activity occurs as a precursor to most large eruptions. Rarely, because of complex interactions, it may appear to settle just before an eruption. Such tectonic events can predict eruptions in long- dormant volcanoes and the size of the magma pocket. Some notable examples of eruptions preceded by volcano tectonic earthquakes include ones at

Nevado del Ruiz Nevado del Ruiz (), also known as La Mesa de Herveo () is a volcano on the border of the departments of Caldas and Tolima in Colombia, being the highest point of both. It is located about west of the capital city Bogotá. It is a stratovolca ...

(1985), Pinatubo (1991), Unzen (1990), and Cotopaxi (2002). Quakes with volcano-tectonic characteristics accompany magmatic intrusions in near real time.

Use in monitoring volcanoes

Nearly every recorded volcanic eruption has been preceded by some form of earthquake activity beneath or near the volcano. This does not mean that always this activity will give sufficient warning of an eruption. However, for individual volcanoes, the relationship between earthquakes and magma movement or possible eruptions has resulted in approximately 200 of the world's volcanoes being seismically monitored. The recording of several years of background seismic data has allowed classification of volcanic earthquakes. These earthquakes tend to occur in swarms as opposed to mainshock–aftershock sequences, have smaller maximum sizes than tectonic structure earthquakes, have similar waveform patterns, increase in number before eruptions, and occur near or beneath the site of the eruption. Volcano tectonic earthquake seismicity typically originates lateral to the site of the volcanic eruption to come, at tectonic fault structures a few kilometres away. Such earthquakes have a large non-double couple component to their

focal mechanism The focal mechanism of an earthquake describes the Fault (geology)#Slip.2C heave.2C throw, deformation in the Hypocenter, source region that generates the seismic waves. In the case of a Fault (geology), fault-related event, it refers to the ori ...

. Other types of seismic activity monitored in relation to

volcanoes A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

and their eruptions are long period

seismic wave A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large ma ...

s (caused by sudden sporadic movement of magma that had previously not been moving due to a blockage), and harmonic tremor (indicating steady magma movement).

References

{{DEFAULTSORT:Volcano Tectonic Earthquake Volcanism Seismology