Where it is and what it carries
The Sunda Plate covers about 8.9 million square kilometers, or 1.75% of Earth’s surface. It carries all of Malaysia, Cambodia, Brunei and Singapore, 81.3% of the Philippines, 63.5% of Indonesia, 62% of Thailand, 54.2% of Vietnam and 32.4% of Laos. Its seafloor includes the South China Sea and the Java Sea.
The plate’s core is Sundaland, a block of continental crust that includes the Malay Peninsula, Sumatra, Java, Borneo and the shallow Sunda Shelf. Around this quiet core, the plate’s edges are crowded with trenches, island arcs and volcanoes.
What happens at its edges
The longest boundary, 3,294 km, is the Sunda Trench (often called the Java Trench) south of Sumatra and Java. Here the Australian Plate subducts northward at about 4.6-6.9 cm/yr. On the east, the Philippine Sea Plate sinks beneath the Philippines along 2,882 km, mainly at the Philippine Trench, at about 9.2-10.8 cm/yr.
To the northwest, a 1,783 km boundary with the Burma Plate combines spreading in the Andaman Sea with strike-slip faulting, moving at about 2.8-5.7 cm/yr. To the north, a 2,026 km boundary with the Eurasian Plate mixes collision, transform and rift segments at about 2.6-2.7 cm/yr, and a 906 km boundary with the Yangtze Plate is mostly transform at about 1.4-1.5 cm/yr.
Eastern Indonesia is a puzzle of microplates. The Sunda Plate converges with the Molucca Sea Plate at about 0.5-4.7 cm/yr and with the Banda Sea Plate at about 0.9-3.4 cm/yr. It slides past the Timor Plate at about 4.1 cm/yr, and its short boundary with the Bird’s Head Plate moves at about 10.7 cm/yr.
Why geologists separate it
Older maps place all of Southeast Asia on the Eurasian Plate. GPS surveys show that Sundaland moves eastward relative to Eurasia as a fairly rigid block, so PB2002 and many later models treat it as its own plate. Its boundary with Eurasia to the north is broad and diffuse, which is one reason the split is debated.
Earthquakes and volcanoes
The dataset lists 384 earthquakes of magnitude 6.5 or larger on the plate since 1900, six of them magnitude 8 or more. The largest is the 2005 Nias earthquake off Sumatra (M8.6), followed by the 2007 Bengkulu earthquake (M8.4). The southern Philippines produced the 1918 Celebes Sea earthquake off Mindanao (M8.3) and the 1976 Moro Gulf earthquake (M7.9), whose tsunami struck the Mindanao coast. The list also includes the 1977 Sumba earthquake (M8.3) in the Lesser Sunda Islands. The 2004 Sumatra-Andaman earthquake (M9.1) happened just to the north, on the Burma Plate.
The plate holds 87 volcanoes in the dataset. Java and Sumatra carry Merapi, Semeru and Marapi, and Krakatau in the Sunda Strait produced the catastrophic 1883 eruption. In the Philippines, Mayon, Taal, Kanlaon and Bulusan are among the most active.