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Microplate · oceanic crust

Mariana Plate

The Mariana Plate is an oceanic microplate in the western Pacific that carries Guam and the Northern Mariana Islands. The Pacific Plate subducts beneath its eastern edge at the Mariana Trench, the deepest trench on Earth, while a back-arc basin opens behind it.

Area
420,773 km²
Share of Earth
<0.1%
Size rank
30 of 52
Avg boundary speed
4.8 cm/yr
Map showing the location of the Mariana Plate and its neighbors Mariana Philippine Sea Open on interactive map

Boundaries of the Mariana Plate

3,549 km of boundary in total: 51% convergent, 41% divergent, 8% transform. Speeds are relative motion between the two plates, from the PB2002 model.

Neighboring plate Boundary type Main features Shared length Relative speed
Pacific Plate Convergent Subduction zone, Oceanic transform fault 1,867 km 4.9-7.7 cm/yr
Philippine Sea Plate Divergent Mid-ocean spreading ridge, Oceanic transform fault 1,682 km 0.9-5.6 cm/yr

A plate between a trench and a back-arc basin

The Mariana Plate is a small oceanic plate of about 421,000 square kilometers, or 0.08% of Earth’s surface. It is a narrow sliver that carries the Mariana island arc, including all of Guam and the Northern Mariana Islands.

The plate exists because the Mariana arc has split away from the Philippine Sea Plate. Between them, the Mariana Trough is a back-arc basin where new seafloor forms. As the trough widens, the arc and its plate move east toward the trench. Many simpler maps leave this strip as part of the Philippine Sea Plate, but PB2002 treats it as its own plate.

What happens at its edges

The eastern edge is the Mariana Trench, where the Pacific Plate subducts westward beneath the Mariana Plate. This 1,867 km boundary moves at about 4.9-7.7 cm/yr. Near the plate’s southwestern corner lies the Challenger Deep, the deepest known point in the oceans at nearly 11 km below sea level. The Pacific crust here is some of the oldest seafloor on Earth, and it sinks almost vertically into the mantle.

The western edge is the 1,682 km boundary with the Philippine Sea Plate along the Mariana Trough. PB2002 classifies most of it as an oceanic spreading ridge, with transform offsets and a short rift section. The spreading rate ranges from about 0.9 to 5.6 cm/yr.

Earthquakes and volcanoes

The dataset lists 43 earthquakes of magnitude 6.5 or larger on the plate since 1900, none of them magnitude 8. The largest is the 1993 Guam earthquake (M7.8), centered south of the island at about 59 km depth. Others include the 1940 Mariana Islands earthquake (M7.7) and the 2016 Pagan earthquake (M7.7) at about 196 km depth, inside the sinking Pacific slab. Large Mariana earthquakes tend to be smaller than those in Japan or Chile, which geologists link to the weak coupling between the plates at this steep, old subduction zone.

The plate holds 26 volcanoes in the dataset. Anatahan had its first recorded eruption in 2003, and Pagan erupted strongly in 1981. Many others are submarine, such as NW Rota-1 and Ahyi, along with active vents on the spreading center of the Mariana Trough.

Countries on the Mariana Plate

Share of each country's land area that lies on this plate.

Largest earthquakes on the Mariana Plate

43 earthquakes of magnitude 6.5 or more since 1900 had their epicenter on this plate. Data: USGS.

EarthquakeMagnitudeYearDepth
32 km S of Inarajan Village, Guam · Guam M7.8 1993 59 km
Mariana Islands region · Northern Mariana Islands M7.7 1940 15 km
Pagan region, Northern Mariana Islands · Northern Mariana Islands M7.7 2016 196 km
Volcano Islands, Japan region · Japan M7.6 2000 127 km
Northern Mariana Islands · Northern Mariana Islands M7.5 1902 –
Volcano Islands, Japan region · Japan M7.5 1934 35 km
Mariana Islands region · Northern Mariana Islands M7.2 1905 200 km
Pagan region, Northern Mariana Islands · Northern Mariana Islands M7.2 1930 25 km

Volcanoes on the Mariana Plate

The Smithsonian Global Volcanism Program lists 26 Holocene volcanoes on this plate. The most recently active:

See all volcanoes on the live map

Frequently asked questions

Is the Mariana Trench on the Mariana Plate?

The Mariana Trench marks the boundary between the Pacific Plate and the Mariana Plate. The Pacific Plate bends down into the trench and slides beneath the Mariana Plate, so the trench floor is Pacific seafloor while the islands to the west sit on the Mariana Plate.

Why is the Mariana Trench so deep?

The Pacific seafloor entering the trench is very old, cold and dense, so it sinks steeply into the mantle. The Mariana Plate is also moving away from the trench as the Mariana Trough opens behind it, so the trench is not filled by a pile-up of crust. Together these let the trench reach nearly 11 km at the Challenger Deep.

Are the Mariana Islands volcanic?

Yes. The northern Mariana Islands, such as Pagan, Anatahan and Farallon de Pajaros, are active volcanoes fed by magma that forms above the subducting Pacific Plate. The southern islands, including Guam and Saipan, are older volcanic islands capped by limestone.

How big is the Mariana Plate?

The Mariana Plate covers about 420,773 km² (162,461 sq mi), roughly <0.1% of Earth's surface. That makes it the 30th largest of the 52 plates in the PB2002 model.

How fast does the Mariana Plate move?

Measured against its neighbors, the Mariana Plate moves at an average of 4.8 cm/yr (1.9 in/yr) along its boundaries. The fastest motion is against the Pacific Plate, where relative speeds reach 7.7 cm/yr on a convergent boundary.

What countries are on the Mariana Plate?

Countries mostly on the Mariana Plate: Guam and Northern Mariana Islands. Shares are measured by land area using Natural Earth outlines.

What plates border the Mariana Plate?

The Mariana Plate shares boundaries with 2 plates: the Pacific Plate (convergent), the Philippine Sea Plate (divergent).

All 52 tectonic plates