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Microplate · oceanic crust

Balmoral Reef Plate

The Balmoral Reef Plate is a small oceanic microplate in the North Fiji Basin, northwest of Fiji. It is bounded by spreading ridges and transform faults, and the dataset records no earthquakes of magnitude 6.5 or larger on it since 1900.

Area
195,387 km²
Share of Earth
<0.1%
Size rank
40 of 52
Avg boundary speed
3.5 cm/yr
Map showing the location of the Balmoral Reef Plate and its neighbors Balmoral Reef New Hebrides Conway Reef Open on interactive map

Boundaries of the Balmoral Reef Plate

2,236 km of boundary in total: 10% convergent, 43% divergent, 47% 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 Divergent Oceanic transform fault, Mid-ocean spreading ridge 978 km 2.2 cm/yr
Australian Plate Transform Oceanic transform fault, Continental transform fault 544 km 6.9-6.9 cm/yr
New Hebrides Plate Divergent Mid-ocean spreading ridge, Oceanic transform fault 442 km 2.1-3.9 cm/yr
Conway Reef Plate Convergent Oceanic convergent boundary, Oceanic transform fault 272 km 1.5-2.4 cm/yr

Where it is

The Balmoral Reef Plate covers about 195,000 km² of seafloor in the northern part of the North Fiji Basin, between Vanuatu and Fiji. It carries no land in the dataset and takes its name from Balmoral Reef.

Like the neighboring Conway Reef Plate, it is one of the blocks that the PB2002 model uses to describe how the North Fiji Basin is opening. The basin formed behind the Vanuatu arc as the arc swung clockwise away from Fiji. Instead of one ridge, several short spreading centers and transform faults split the young seafloor into pieces. All of the crust on the plate formed as the basin opened, so it is much younger than the Pacific seafloor farther north.

What happens at its edges

Its longest boundary, 978 km, is with the Pacific Plate to the north. It combines spreading ridges, transform faults and a short rift, and relative motion is about 2.2 cm/yr.

The boundary with the Australian Plate, which carries Fiji, is mostly transform. Here the two plates slide past each other at about 6.9 cm/yr, the plate’s fastest relative motion. This boundary is part of the Fiji Fracture Zone, a system of strike-slip faults that runs west from the Fiji islands into the basin.

To the west, the plate spreads away from the New Hebrides Plate along 442 km of ridge, at about 3 cm/yr on average. To the south, it meets the Conway Reef Plate along a short boundary of slow convergence and transform faulting, at about 1.9 cm/yr.

A quiet microplate

The dataset lists no earthquakes of magnitude 6.5 or larger on the Balmoral Reef Plate since 1900 and no volcanoes. Its neighbors are far more active: the New Hebrides Plate to the west has recorded more than 200 large quakes. The difference comes from the type of boundary. Spreading ridges and transforms in young, hot crust release stress in small, frequent quakes, while subduction zones like the New Hebrides Trench can lock up and fail in great earthquakes.

Because so little of the plate rises above sea level and few large quakes outline its edges, its boundaries are among the least certain in the PB2002 model.

Countries on the Balmoral Reef Plate

No country sits mainly on the Balmoral Reef Plate. Its surface is almost entirely ocean floor.

Frequently asked questions

Why has the Balmoral Reef Plate had no large earthquakes?

Its boundaries are spreading ridges and transform faults in young, thin oceanic crust. That kind of crust is hot and weak, so it breaks in frequent small and moderate quakes rather than storing up strain for great ones. The dataset lists no quakes of magnitude 6.5 or larger on the plate since 1900, although smaller ones do occur.

Is the Balmoral Reef Plate a real plate?

It is a block that moves independently in the PB2002 model, but its existence is less certain than that of large plates. It has almost no land for GPS stations, so its motion comes from seafloor spreading patterns and earthquake data. Other studies divide the North Fiji Basin into different blocks, and many maps do not show it at all.

Where is the Balmoral Reef Plate?

It lies in the North Fiji Basin, in the open ocean between Vanuatu to the west and Fiji to the east. The Pacific Plate lies to its north, and the Conway Reef Plate to its south.

How big is the Balmoral Reef Plate?

The Balmoral Reef Plate covers about 195,387 km² (75,439 sq mi), roughly <0.1% of Earth's surface. That makes it the 40th largest of the 52 plates in the PB2002 model.

How fast does the Balmoral Reef Plate move?

Measured against its neighbors, the Balmoral Reef Plate moves at an average of 3.5 cm/yr (1.4 in/yr) along its boundaries. The fastest motion is against the Australian Plate, where relative speeds reach 6.9 cm/yr on a transform boundary.

What countries are on the Balmoral Reef Plate?

No country sits mainly on the Balmoral Reef Plate; it is almost entirely ocean floor. The nearest land is part of the neighboring plates.

What plates border the Balmoral Reef Plate?

The Balmoral Reef Plate shares boundaries with 4 plates: the Pacific Plate (divergent), the Australian Plate (transform), the New Hebrides Plate (divergent), the Conway Reef Plate (convergent).

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