The Earth is covered in enormous and irregular shaped rocks (known as plates) that are part of the planet’s lithosphere layer (the Earth’s crust and the Earth’s mantle). The Earth’s tectonic plates vary in size from as small as a few hundred kilometers across to thousands of kilometers.
Tectonic plates divide up the Earth’s crust. Earthquakes and volcanic activity are mostly concentrated along the boundaries of these plates. Many earthquakes happen around the mid-ocean ridges and the major faults that occur at the plates’ boundaries.
The crust or upper mantle, which extends from the Earth’s surface to about 800 kilometers (500 miles) below the surface, is where earthquakes occur.
The majority of tectonic plates contain both oceanic and continental crust. The Pacific Plate, on the other hand, is primarily composed of oceanic crust.
Volcanoes and earthquakes tends to be more concentrated at the margins of tectonic plates, particularly in the Pacific Ring of Fire where the Pacific Plate meets other tectonic plates like the North American Plate.
Types of Tectonic Plates
There are three categories of plates, based on the total area of the plate: major (or primary) plates, minor (or secondary) plates.
Major plates tend to be greater than 20 million km2 in area. Minor plates are less than 20 million km2 in size but greater than one million km2. Plates that are smaller than one million km2 are known as microplates.
Major Tectonic Plates
Major tectonic plates tend to be at least 20 million square kilometers in area. The seven major tectonic plates are:
- African Plate
- Antarctic Plate
- Eurasian Plate
- Australian Plate
- North American Plate
- Pacific Plate
- South American Plate
Earth’s Minor Plates and Microplates
Minor tectonic plates are those that are more than a million square kilometers but have an area of less than 20 million square kilometers.
Minor tectonic plates include: Arabian Plate, Nazca Plate, and Juan de Fuca Plate.
The Earth’s tectonic plates less than one million square kilometers are known as microplates. Examples include: the Bismark Plate, Mariana Plate, Easter Plate, and Juan Fernandez Plate.
Map of Tectonic Plates
This geology map created by the USGS highlights all the major and some of the Earth’s minor tectonic plates.
The map also shows the convergent boundaries like the dividing line between the Indian Plate and the Eurasian plate in the Himalayas. Another convergent boundary is in west South America where the Nazca Plate and the South American Plate meet.
Also shown on the map are divergent boundaries like the boundary between the North America Plate and the Eurasian Plate.
Plate Tectonics and Continental Drift Theory
The Earth’s plates are always slowly moving. This movement is responsible for the creation of mountains and the growing ocean floor. The Atlantic Ocean, for example, grows about an inch of new seafloor every year.
Plate tectonics expands on the continental drift theory and is based on the concept that there are seven or eight (depending on how the plates are defined) major plates and numerous minor plates and microplates that are made up of either the oceanic or continental lithosphere.
The drifting and shifting of the Earth’s plates is believed to be responsible for the rift that started 180 million years ago in the supercontinent, Pangea. The rift led to the Americas and Africa drifting apart and the subsequent formation of the Atlantic Ocean.
This informative video provides a concise overview of plate tectonics starting with Alfred Wegner’s continental drift theory, which paved the way for tectonic plate theory, before continuing on to a discussion about the types of plates and plate boundaries and how plates shape our earth.
Find Tectonic Plate GIS Data
There a few sources of freely available tectonic plate data that is available in various GIS data formats (such as shapefiles and KMZ).
In 2003, Peter Bird published a global data set of plate boundaries (Citation: An updated digital model of plate boundaries, Geochemistry Geophysics Geosystems, 4(3), 1027, doi:10.1029/2001GC000252, 2003).
This data has since been transformed from the original text files into shapefile and GeoJSON formats and is available via Github. This dataset contains files that represent global tectonic plates, orogens and plate boundaries and is freely available for downloading and use.
The University of Texas Institute for Geophysics (UTIG) offers plate boundaries in GMT-formatted (ASCII) and KMZ format (Citation: Coffin, M.F., Gahagan, L.M., and Lawver, L.A., 1998, Present-day Plate Boundary Digital Data Compilation. University of Texas Institute for Geophysics Technical Report No. 174, pp. 5. (PDF)).
The geographic datasets are broken out by plate type: ridges (R), trenches (T), or transform faults (F). The data page was compiled as part of the PLATES Project which is a research project focused on plate tectonics and geologic reconstructions. The data page contains additional geological datasets relating to plate tectonics.
The USGS hosts numerous files relating to earthquakes and plate tectonics on this data page. All GIS data is available in KMZ format.
Plate Visualization Software – GPlates
GPlates is an open source desktop software for the interactive visualisation of plate-tectonics developed in 2012 as a collaborative effort by the University of Sydney, the California Institute of Technology, and the Geological Survey of Norway.
GPlates runs on Windows, Linux, and MacOS X and allows users to “visualize and manipulate plate-tectonic reconstructions and associated data through geological time”.
A sample set of geologic data accompanies the GPlates application but additional tectonic plate data is available via the GPlates-compatible data page
More:
Williams, S. E., Müller, R. D., Landgrebe, T. C., & Whittaker, J. M. (2012). An open-source software environment for visualizing and refining plate tectonic reconstructions using high-resolution geological and geophysical data sets. GSA Today, 22(4/5), 4-9. Retrieved from http://www.geosociety.org/gsatoday/archive/22/4/article/i1052-5173-22-4-4.htm
This article was originally published on December 28, 2016 and has been since updated.
