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Microplate · oceanic crust

Conway Reef Plate

The Conway Reef Plate is a small oceanic microplate in the southern North Fiji Basin, between Vanuatu and Fiji. It is bounded mostly by young spreading ridges and moves away from the New Hebrides Plate as the basin opens.

Area
144,452 km²
Share of Earth
<0.1%
Size rank
43 of 52
Avg boundary speed
5.0 cm/yr
Map showing the location of the Conway Reef Plate and its neighbors Conway Reef New Hebrides Balmoral Reef Open on interactive map

Boundaries of the Conway Reef Plate

1,860 km of boundary in total: 12% convergent, 67% divergent, 21% transform. Speeds are relative motion between the two plates, from the PB2002 model.

Neighboring plate Boundary type Main features Shared length Relative speed
Australian Plate Divergent Mid-ocean spreading ridge, Oceanic transform fault 850 km 1.2-5.5 cm/yr
New Hebrides Plate Divergent Mid-ocean spreading ridge, Oceanic transform fault 738 km 5.6-11.8 cm/yr
Balmoral Reef Plate Convergent Oceanic convergent boundary, Oceanic transform fault 272 km 1.5-2.4 cm/yr

Where it is and why it is separate

The Conway Reef Plate covers about 144,000 km² of seafloor in the southern North Fiji Basin, between Vanuatu and Fiji. It carries no land in the dataset. Its name comes from Conway Reef, a remote reef southwest of Fiji.

The North Fiji Basin is a back-arc basin that has opened over the past several million years as the Vanuatu arc swung clockwise away from Fiji. It does not open along one straight ridge. Instead, several spreading ridges and transform faults break it into small blocks, and PB2002 treats the Conway Reef Plate as one of them. Because there is almost no land on it for GPS stations, its motion is worked out from seafloor features and earthquakes, so its exact boundaries are less certain than those of large plates.

What happens at its edges

The 850 km boundary with the Australian Plate, which carries Fiji, is its longest. It is mostly spreading ridge with some transform faults, and relative speeds average about 2.9 cm/yr, ranging from about 1.2 to 5.5 cm/yr.

The most active edge is the 738 km boundary with the New Hebrides Plate to the west. This is the main spreading ridge of the North Fiji Basin, where the plates move apart at about 8.7 cm/yr on average and up to about 11.8 cm/yr. That is fast for a back-arc basin, faster than many mid-ocean ridges.

To the north, the plate meets the Balmoral Reef Plate along 272 km of slow convergence and transform motion, at about 1.9 cm/yr.

Earthquakes

The dataset lists eight earthquakes of magnitude 6.5 or larger since 1900, none reaching magnitude 8. Shallow quakes include an M7.1 event in February 2000 and an M6.8 event in 1972 about 281 km west-northwest of Lautoka, Fiji. Two quakes on the same day in November 1934, M6.6 and M6.5, struck near the southern end of the plate.

The largest event was very deep. In October 2021, an M7.3 quake struck 527 km down, followed a week later by an M6.9 quake at 535 km. These quakes do not come from the plate itself but from old subducted lithosphere lying far below it. The dataset lists no volcanoes on the plate.

Countries on the Conway Reef Plate

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

Largest earthquakes on the Conway Reef Plate

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

EarthquakeMagnitudeYearDepth
Vanuatu region · Vanuatu M7.3 2021 527 km
Vanuatu region · Vanuatu M7.1 2000 33 km
Vanuatu region · Vanuatu M6.9 2021 535 km
281 km WNW of Lautoka, Fiji · Fiji M6.8 1972 10 km
southeast of the Loyalty Islands · New Caledonia M6.6 1990 33 km
Vanuatu region · Vanuatu M6.6 1934 15 km
southeast of the Loyalty Islands · New Caledonia M6.5 1934 15 km
Fiji region · Fiji M6.5 2000 33 km

Frequently asked questions

Where is Conway Reef?

Conway Reef, called Ceva-i-Ra in Fijian, is a small, isolated reef with a tiny sand cay in the open ocean southwest of Fiji's main islands. It is administered by Fiji. The PB2002 model names the surrounding microplate after it.

Why are there deep earthquakes under the Conway Reef Plate?

The plate itself is young seafloor that is spreading, not sinking, so its own boundaries produce shallow quakes. The deep quakes, such as the M7.3 event at 527 km in October 2021, happen in old slab material that sank into the mantle beneath the North Fiji Basin. Geologists still debate whether that slab is a detached piece of an older subduction zone or part of the Tonga slab extending west.

Do all geologists recognize the Conway Reef Plate?

No. The North Fiji Basin is a complicated zone of short spreading ridges and transform faults, and different studies divide it into different blocks. PB2002 defines the Conway Reef and Balmoral Reef plates from seafloor structure and earthquake patterns, but many maps simply show the whole basin as part of the Australian or Pacific plates.

How big is the Conway Reef Plate?

The Conway Reef Plate covers about 144,452 km² (55,773 sq mi), roughly <0.1% of Earth's surface. That makes it the 43rd largest of the 52 plates in the PB2002 model.

How fast does the Conway Reef Plate move?

Measured against its neighbors, the Conway Reef Plate moves at an average of 5.0 cm/yr (2.0 in/yr) along its boundaries. The fastest motion is against the New Hebrides Plate, where relative speeds reach 11.8 cm/yr on a divergent boundary.

What countries are on the Conway Reef Plate?

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

What plates border the Conway Reef Plate?

The Conway Reef Plate shares boundaries with 3 plates: the Australian Plate (divergent), the New Hebrides Plate (divergent), the Balmoral Reef Plate (convergent).

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