How Deep are the Earth’s Tectonic Plates?

Elizabeth Borneman


The study of Earth’s tectonic plates keeps researchers of all disciplines busy. Seismologists are particularly interested in the behavior of tectonic plates as they relate to earthquakes and other activity that affects the surface of the earth.

As you can imagine, studying tectonic plates requires no uncertain amount of creativity and technology; located deep beneath the surface, researchers have to come up with unique ways to study the shape, size, and movement of plates around the world.

Using Earthquake Vibrations to Measure the Depth of Tectonic Plates

Seismologists can use the vibrations caused by earthquakes to measure how deep the tectonic plates go. Seismic waves are able to penetrate the various layers beneath our feet to reveal the makeup and density of the rocky layers.

Using data compiled from earthquakes around the world, seismic waves have shown a layer of melted rock material that exists between 130-190 kilometers beneath the ground. (See also: A Jet Stream in the Middle of the Earth)

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Seismologists have long debated the depth of the Earth’s tectonic plates. As technology has caught up, researchers have been able to use seismic data to extrapolate more information about the boundaries of the world’s tectonic plates.

Seismologists estimate that the rigid rock material that makes up our landmasses extends about 175 kilometers below the surface, and is resting on a slightly more liquid rock. New seismic data could extend that rigid rock layer to 200 or 300 feet, however, and shows more of a gradient leading from cold, hard rock to hotter, more molten material.

Diagram showing the earth's upper crusts and how tectonic plate movement leads to volcano formation and mountains.
Image: USGS

What is the Difference Between Earthquake Vibrations and Seismic Waves?

Researchers have been able to create a better picture of tectonic plates by using both earthquake vibrations and seismic waves. Earthquake vibrations happen closer to the surface, while seismic waves travel much deeper below the surface.

Both of these elements show seismologists different data that can be combined to create a bigger picture of what our tectonic plates are doing.

Using Seismic Waves to Visualize Tectonic Plates

Seismic waves penetrate deep into the earth, but they also bounce off different layers of the tectonic plates. By analyzing the data surrounding seismic waves, scientists can create a picture of what they think the tectonic plate looks like under the surface.

This data is important not only for answering some long-held scientific questions, but for the future of seismology as well. The data allows researchers to understand more about the movement of tectonic plates and their composition; they are also able to establish baseline readings for each tectonic plate, which can be used again if the plates start to undergo changes.

This research also assists with the study of plate tectonics. Scientists could make better simulations of the movement of the plates and better be able to predict earthquakes and volcanic activity. Active monitoring of the Earth’s crust and the material it rests on could lead to better predictions of volcanic or earthquake activity that could pose a risk to humans on land.

By establishing what we know about tectonic plates, we can create an idea of what the plates looked like in the past and what they could resemble in the future. Seismologists and other researchers will keep working on improving technology to monitor seismic waves and the depth of Earth’s many tectonic plates.

The study:

Tharimena, S., Rychert, C., & Harmon, N. (2017). A unified continental thickness from seismology and diamonds suggests a melt-defined plate. Science, 357(6351), 580-583.

Commentary on the study:

Savage, B. (2017). A seismic shift in continental tectonic plates. Science, 357(6351), 549-550.

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About the author
Elizabeth Borneman
My name is Elizabeth Borneman and I am a freelance writer, reader, and coffee drinker. I live on a small island in Alaska, which gives me plenty of time to fish, hike, kayak, and be inspired by nature. I enjoy writing about the natural world and find lots of ways to flex my creative muscles on the beach, in the forest, or down at the local coffee shop.