Intraplate earthquake

An intraplate earthquake is an earthquake that happens inside a tectonic plate. These earthquakes are less common than interplate earthquakes, which happen at the edges of tectonic plates. An earthquake that happens inside a subducting plate is called an intraslab earthquake.

Buildings far from plate edges are often not made to withstand earthquakes, so large intraplate earthquakes can cause a lot of damage. Some well-known examples are the 2001 Gujarat earthquake, the 2011 Christchurch earthquake, the 2012 Indian Ocean earthquakes, the 2017 Puebla earthquake, the 1811–1812 New Madrid earthquakes, and the 1886 Charleston earthquake. These events show why it is important to learn about all kinds of earthquakes, even those that happen far from plate boundaries.

Description

The Earth's crust is made up of large pieces called tectonic plates that move very slowly. These plates move on top of hot currents in the mantle. When plates move in different directions, they can bump into each other or slide past one another. This often causes earthquakes at their edges.

Earthquakes that happen far from where plates meet are called intraplate earthquakes. These are less common. They can happen where old cracks or weaknesses exist in the Earth's crust. This makes it easier for shaking to occur when the ground is under pressure. Intraslab earthquakes happen inside a sinking plate. They can release more shaking energy than earthquakes at plate edges, even if they seem smaller.

Examples

Some well-known intraplate earthquakes happened far from plate boundaries. For example, there was a quake in Mineral, Virginia in 2011, and another in Newcastle, New South Wales in 1989. In New Madrid in 1811 and 1812, an earthquake was very strong for an area not near plate edges.

Other examples include the Boston (Cape Ann) earthquake of 1755, quakes felt in New York City in 1737 and 1884, and the Charleston earthquake in South Carolina in 1886. In 2001, a large intraplate earthquake hit Gujarat, India, causing damage. In 2017, a earthquake shook Botswana, and in 1888, an intraplate quake was felt in cities along the Río de la Plata in South America.

Causes

Many cities need to be ready for the seismic risk of a rare, large intraplate earthquake. We often don’t know why these earthquakes happen. Sometimes, the fault that causes the earthquake is deep underground and hard to find. Some research shows that fluids moving through old fault zones can start these quakes. This makes it hard to predict the seismic hazard for a city, especially if only one earthquake has ever been recorded there. Scientists are studying the fault mechanics to learn more.

Intraplate earthquakes can also happen because of natural processes like the melting of ice sheets or the wearing away of land by wind and water.

Prediction

Scientists study intraplate earthquakes to learn why they happen and when they might happen again. They use seismometers to find very small earthquakes. These tiny quakes often form lines that help scientists understand the faults that cause earthquakes. Sometimes, loud sounds from freezing water, called cryoseisms, can seem like intraplate earthquakes.

Intraslab earthquake

In seismology, an intraslab earthquake happens inside a subducting plate, called a slab. These earthquakes often occur in older, colder slabs and can happen very deep underground, more than 500 km below the surface. They can also cause shallower earthquakes that may affect nearby cities. Some well-known intraslab earthquakes include the 1970 Ancash earthquake, the 2001 Nisqually, and the 1949 Olympia earthquakes.