An interplate earthquake occurs at the boundary between two
tectonic plate
Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
s. 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 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 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 (geology), fault along a plate boundary where the motion (physics), motion is predominantly Horizontal plane, horizontal. It ends abruptly where it connects to another plate boundary, either an ...
boundary, vertical if along a convergent boundary (i.e.
subduction
Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
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 earthquake
Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthq ...
s, which include most of the Earth's largest earthquakes.
Intraplate earthquake
An intraplate earthquake occurs in the ''interior'' of a Plate tectonics, tectonic plate, in contrast to an interplate earthquake on the ''boundary'' of a tectonic plate. They are relatively rare compared to the more familiar interplate earthqu ...
s 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 (geology), fault along a plate boundary where the motion (physics), motion is predominantly Horizontal plane, horizontal. It ends abruptly where it connects to another plate boundary, either an ...
: 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 List of tectonic plates, tectonic plates that are moving away fr ...
: 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
The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake.
Magnitude scales measure the inherent force or ...
, 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 , ) 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 underwater explosions (including detonations, ...
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 earthquake
An intraplate earthquake occurs in the ''interior'' of a Plate tectonics, tectonic plate, in contrast to an interplate earthquake on the ''boundary'' of a tectonic plate. They are relatively rare compared to the more familiar interplate earthqu ...
s or
tsunami earthquake
In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater Seismic magnitude scales, magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanam ...
s 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
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
(especially
California
California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
and
Alaska
Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...
), the northeastern Mediterranean region (
Greece
Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
,
Italy
Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
, and
Turkey
Turkey, officially the Republic of Türkiye, is a country mainly located in Anatolia in West Asia, with a relatively small part called East Thrace in Southeast Europe. It borders the Black Sea to the north; Georgia (country), Georgia, Armen ...
in particular),
Iran
Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq to the west, Turkey, Azerbaijan, and Armenia to the northwest, the Caspian Sea to the north, Turkmenistan to the nort ...
,
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
,
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
,
India
India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...
,
Japan
Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...
, and parts of
China
China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
.
Major earthquakes (magnitude ≥ 9.0) since 1900
See also
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Forearc
A forearc is a region in a subduction zone between an oceanic trench and the associated volcanic arc. Forearc regions are present along convergent margins and eponymously form 'in front of' the volcanic arcs that are characteristic of convergen ...
References
Plate tectonics
Types of earthquake