Introduction
The Sunda Plate is a minor tectonic plate in the Eastern Hemisphere that straddles the equator and constitutes the principal lithospheric foundation for much of Southeast Asia. Its geographic and geologic role is central to the arrangement of continental fragments and island arcs across the equatorial sector of the region. Although traditionally considered a portion of the Eurasian Plate, contemporary geodetic observations (notably GPS) reveal that the Sunda Plate behaves as an independent plate, translating eastward relative to Eurasia at roughly 10 mm yr⁻¹.
Extent
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The Sunda Plate underlies a broad sector of Southeast Asia, encompassing the South China Sea and the Andaman Sea and extending across southern portions of Vietnam, Myanmar, Laos and Thailand. It includes the territories of Malaysia, Singapore and Cambodia, the southern Philippines, and major Indonesian island groups such as Bali, Lombok (West Nusa Tenggara), Borneo, Sumatra, Java and parts of Sulawesi.
Its eastern margin is a mosaic of microplates and collision zones, abutting the Philippine Mobile Belt, the Molucca Sea Collision Zone and associated small plates (Molucca Sea, Banda Sea, Timor), producing a structurally complex boundary. To the south and west the plate meets the Australian Plate along a broad convergent margin that governs subduction and deformation of the Sunda Plate’s southern and western rims. By contrast, the northern margin, adjacent to the Burma, Eurasian and Yangtze plates, is relatively tectonically quiet.
Subduction of the Indo‑Australian Plate beneath the Sunda Plate occurs along the Sunda (Java) Trench and is the principal source of large earthquakes and tsunamis affecting adjacent seas and coastlines. Near Timor the subduction history is atypical: an original oceanic–oceanic regime evolved into a configuration in which continental lithosphere of the Indo‑Australian Plate is being drawn beneath an oceanic upper plate, a legacy of earlier consumption of oceanic lithosphere. Geodetic (GPS) data show that the lower Indo‑Australian Plate is the main driver of deformation across the Sunda–Banda arc system; imposed plate motions produce predominant shortening, concentrated in forearc and backarc sectors and expressed as active crustal shortening and mountain building within the Banda Orogen. Overall, the plate’s eastern, southern and western margins are tectonically intricate and seismically active, while its northern boundary remains comparatively quiescent.