Intraplate earthquake

An intraplate earthquake is an earthquake which occurs in the interior of a tectonic plate. They are relatively rare compared to the more familiar interplate earthquakes, which occur on the boundaries of tectonic plates. An earthquake that occurs within a subducting plate is known as an intraslab earthquake.

Because buildings far from plate boundaries are rarely protected with seismic retrofitting, large intraplate earthquakes can inflict heavy damage. Some notable examples include the devastating 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 how important it is to understand all kinds of earthquakes, even those that happen away from plate edges.

Description

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

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

Examples

Some well-known intraplate earthquakes happened in places far from plate boundaries. For example, there was a quake in Mineral, Virginia in 2011 with an estimated magnitude of 5.8, and another in Newcastle, New South Wales in 1989. In New Madrid in 1811 and 1812, an earthquake reached an estimated magnitude as high as 8.6, which 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 widespread damage. In 2017, a magnitude 6.5 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 must be prepared for the seismic risk of a rare, large intraplate earthquake. The reason these earthquakes happen is often unclear. In many cases, the fault causing the earthquake is deep underground and hard to locate. Some research suggests that fluids moving through old fault zones can trigger these quakes. This makes it challenging to predict the seismic hazard for a city, especially if only one earthquake has been recorded in history. Scientists are working to better understand the fault mechanics behind these events.

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

Prediction

Scientists work to understand why intraplate earthquakes happen and how often they might occur again. They use many seismometers to detect very small earthquakes. These tiny quakes often line up in patterns that help scientists learn about the faults causing the earthquakes. Sometimes, cryoseisms — loud sounds from freezing water — can be confused with intraplate earthquakes.

Intraslab earthquake

In seismology, an intraslab earthquake happens inside a subducting plate, called a slab. These earthquakes are most common in older, colder slabs and can occur at depths deeper than 500 km. They can also cause shallow earthquakes, which can be harmful to nearby cities. Some notable intraslab earthquakes include the 1970 Ancash earthquake, the 2001 Nisqually, and the 1949 Olympia earthquakes.