An interplate earthquake 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 boundary, vertical if along a convergent boundary (i.e. subduction 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:
- Transform fault: Where two boundaries slide laterally relative to each other.
- Divergent boundary: Where two boundaries move apart.
- Convergent boundary: 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. This suggests that the boundaries between plates are significantly weaker than the plates themselves. 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. 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 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.
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!Date
!Latitude
!Longitude
!Depth (km)
!Magnitude
!Location
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|2011-03-11||38.297||142.373||29||9.1||near the east coast of Honshu, Japan
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|2004-12-26||3.295||95.982||30||9.1||off the west coast of northern Sumatra
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|1964-03-28||60.908|| −147.339||25||9.2||Southern Alaska
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|1960-05-22|| −38.143|| −73.407||25||9.5||Bio-Bio, Chile
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|1952-11-04||52.623||59.779||21.6||9||off the east coast of the Kamchatka Peninsula, Russia
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Major earthquakes (magnitude ≥ 9.0) since 1900