An interplate earthquake is an
earthquake
An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in intensity, from ...
that occurs at the boundary between two
tectonic plates. Earthquakes of this type account for more than 90 percent of the total
seismic energy released around the world.
If one plate is trying to move past the other, they will be locked until sufficient stress builds up to cause the plates to slip relative to each other. The slipping process creates an earthquake with relative displacement on either side of the fault, resulting in
seismic waves which travel through the Earth and along the Earth's surface. Relative plate motion can be lateral as along a
transform fault
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subducti ...
boundary, vertical if along a convergent boundary (i.e.
subduction
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...
or thrust/reverse faulting) or a divergent boundary (i.e. rift zone or normal faulting), and oblique, with horizontal and lateral components at the boundary. Interplate earthquakes associated at a subduction boundary are called
megathrust earthquakes, which include most of the Earth's largest earthquakes.
Intraplate earthquakes are often confused with interplate earthquakes, but are fundamentally different in origin, occurring within a single plate rather than between two tectonic plates on a plate boundary. The specifics of the mechanics by which they occur, as well as the intensity of the stress drop which occurs after the earthquake also differentiate the two types of events. Intraplate earthquakes have, on average, a higher stress drop than that of an interplate earthquake and generally higher intensity.
Mechanics
Mechanically, interplate earthquakes differ from other seismic events in that they are caused by motion at the boundary between two tectonic plates. An interplate earthquake event occurs when the accumulated stress at a tectonic plate boundary are released via
brittle failure and displacement along the fault.
There are three types of plate boundaries to consider in the context of interplate earthquake events:
[Bellam, S. S. (2012). ''Assessment of Interplate and Intraplate Earthquakes'' (Doctoral dissertation, Texas A & M University).]
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Transform fault
A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subducti ...
: Where two boundaries slide laterally relative to each other.
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Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent ...
: Where two boundaries move apart.
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Convergent boundary
A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...
: Where one plate moves towards, and potentially subducts beneath, another plate.
Precursory tremors
Scientists have determined that interplate earthquakes are sometimes preceded by an irregular occurrence of small tremors.
Precursory tremors are often associated with slow slip along a plate boundary.
These precursory tremors can sometimes be identified within days or weeks of an interplate earthquake event and allow researchers to anticipate interplate earthquakes and introduce strategies to mitigate damage.
Differences with intraplate earthquakes
Beyond the inherent mechanical differences leading to interplate earthquake events and location of interplate earthquakes on plate boundaries, these seismic occurrences can be differentiated by other means.
Intensity
Interplate earthquakes differ from intraplate earthquakes in that the intensity of intraplate earthquakes exceed those of interplate earthquakes by nearly two points.
Using the
Modified Mercalli Intensity scale, earthquakes are categorized descriptively on a scale from I (not felt) to XII (total destruction) based on observed effects of the seismic event. While the ground accelerations of these two types of events are similar, the resulting intensity of intraplate earthquakes is significantly greater than that of interplate earthquakes
due to the greater energy release (stress drop) across intraplate faults.
Stress drop
Stress drop is a measure of the stress across a fault before and after an earthquake rupture. While intraplate and interplate earthquakes obey similar length proportional scaling laws, interplate earthquakes exhibit stress drop values that are systematically smaller by a factor of 6.
[Scholz, C. H., Aviles, C. A., & Wesnousky, S. G. (1986). Scaling differences between large interplate and intraplate earthquakes. ''Bulletin of the Seismological Society of America'', ''76''(1), 65–70.] This suggests that the boundaries between plates are significantly weaker than the plates themselves.
The reason for the measurable, systemic difference in stress drop between interplate and intraplate earthquakes is not entirely understood.
However, intraplate earthquake models show that stress is distributed uniformly across the fault whereas interplate earthquakes have stress concentrated in specific areas along the boundary.
[Kato, N. (2009). A possible explanation for difference in stress drop between intraplate and interplate earthquakes. ''Geophysical Research Letters,36''(23). doi:10.1029/2009gl040985] Furthermore, interplate earthquakes release stress immediately, as compared to intraplate earthquakes which release stress gradually.
Effects
Subduction erosion
Basal erosion, the process of removal of materials from the underside of the upper plate by the subducting plate, occurs at numerous, but not all, convergent margins. As the process of subduction erosion is not completely understood, a model has been proposed in which basal erosion is supplemented by cyclical, interplate earthquakes.
[Wang, K., Hu, Y., Huene, R. V., & Kukowski, N. (2010). Interplate earthquakes as a driver of shallow subduction erosion. ''Geology,38''(5), 431–434. doi:10.1130/g30597.1] The model suggests that erosion does not occur gradually in subduction zones, but rather in brief episodes of elevated seismicity along the plate boundary.
Tsunamis
Earthquakes are a major factor in the creation of
tsunami
A tsunami ( ; from ja, 津波, lit=harbour wave, ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater exp ...
waves. As interplate earthquakes result in an immediate release of stress along a fault, they produce significant seismic energy and can cause seafloor uplift, generating large waves as the energy from the sudden slip along the fault is transferred to the overlying water body. However, the majority of interplate earthquakes are not intense enough to create tidal waves, with most tsunamis being caused by
intraplate earthquakes or
tsunami earthquakes due to their comparatively slow stress release regimes and proximity to the surface of the Earth.
Major interplate earthquakes
Interplate earthquakes account for over 90% of all
seismic energy released worldwide.
As such, their effects are widespread and interplate earthquake events are numerous. Earthquakes of magnitudes higher than 5 in populated regions are considered highly dangerous and pose a direct threat to human life and property.
Some of the largest, most devastating earthquakes that have occurred in the last century have been identified as interplate events. Some areas of the world that are particularly prone to interplate earthquakes due to the presence of prominent plate boundaries include the west coast of
North America (especially
California
California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the ...
and
Alaska
Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S ...
), the northeastern Mediterranean region (
Greece
Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders wit ...
,
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
, and
Turkey
Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a list of transcontinental countries, transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with ...
in particular),
Iran
Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkm ...
,
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...
,
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...
,
India
India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...
,
Japan, and parts of
China.
Major earthquakes (magnitude ≥ 9.0) since 1900
See also
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Forearc
References
Plate tectonics
Types of earthquake