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A number of studies defined the extent of the Ryukyu Arc geographically and morphologically into three parts: Northern Ryukyu, which includes the [[Ōsumi Islands]]; Central Ryukyu, which includes [[Amami Islands]] and [[Okinawa Islands]]; Southern Ryukyu, which includes [[Miyako Islands]] and [[Yaeyama Islands]].<ref name=":1" /><ref name=":5" /> The northernmost and southernmost parts of the Ryukyu Arc terminate in Kyushu and Taiwan, respectively.<ref name=":9">{{cite report|last1=Foster|first1= H. L.|date=1965|title=Geology of Ishigaki-shima, Ryukyu-retto|series=US Geological Survey, Professional Papers|publisher=US Geological Survey|doi=10.3133/pp399A}}</ref>
The geological and structural features of Southern Ryukyu are quite different from those of Northern and Central Ryukyu; Southern Ryukyu, and Northern and Central Ryukyu may have developed in disparate geological settings before the middle [[Miocene]].<ref name=":1" /> [[Accretionary wedge|Accretionary complexes]] in Northern and Central Ryukyu are considered as the extension of the Outer Zone of Southwest Japan,<ref name=":5" /><ref name=":25">{{cite book|last1=Taira
[[File:Location of the Ryukyu Islands.JPG|thumb|upright=1.5|Location of the Ryukyu Islands.]]
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=== Seismicity ===
The Ryukyu Arc is a site of active [[seismicity]] characterised by shallow earthquakes, given the ongoing convergence between the Philippine Sea Plate and Eurasian Plate.<ref name=":9" /> Seismic data of earthquakes have been used to detect seismic structures below the Ryukyu Arc.<ref name="a">{{cite journal |last1=Roecker
[[File:M≥6.0 (1960-2022) Earthquakes in the Ryukyu Arc.png|thumb|upright=2.2|M≥6.0 (1960-2022) Earthquakes in the Ryukyu Arc. Earthquake data from USGS-ANSS Catalog. Contours in 1 km interval. Figure made with GeoMapApp (www.geomapapp.org) / CC BY / CC BY (Ryan et al., 2009).<ref name="fig" />]]
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Major, but not all, geological units of the Ryukyu Arc are herein summarised.
[[File:Simplified Geological Map of Ishigaki Island.png|thumb|upright=1.5|Simplified Geological Map of Ishigaki Island, after Nakae (2013)<ref name=":6" /> and Nishimura (1998)<ref name=":14" />]]
[[File:Simplified Geological Map of northern Okinawa Island.png|thumb|upright=1.5|Simplified Geological Map of northern Okinawa Island, after Miyagi et al., (2013).<ref>{{cite journal |last1=Miyagi
===Motobu and Yonamine Formations===
The Motobu and Yonamine Formations are [[Permian]] rocks that constitute the basement of the Motobu peninsula of [[Okinawa Island]], Central Ryukyu.<ref name=":10">{{cite journal |last1=Ishibashi
The Motobu Formation consists mainly of [[limestone]] interbedded with [[chert]] and [[phyllite]].<ref name=":11">Flint, D. E., Saplis, R. A., & Corwin, G. (1959). Military geology of Okinawa-jima, Ryukyu-retto. US Army Pacific Office Eng., 5, 88.</ref> The limestone contains [[foraminifera]] fossils of Permian age.<ref name=":9" />
The Yonamine Formation, with strata of interbedded phyllite, [[slate]], [[sandstone]], limestone, greenstone, and chert,<ref name=":11" /> underlies the Motobu Formation<ref name=":12">Konishi, K. (1963). Pre-Miocene basement complex of Okinawa, and the tectonic belts of the Ryukyu Islands. ''Sci. Rep. Kanazawa Univ., 8'', 569–602.</ref> and contains Permian corals.<ref name=":13">Haikawa, T., & Ishibashi, T. (1981). Waagenophyllum (Waagenophyllum) okinawense, a new Permian coral from Okinawa-jima, Ryukyu Islands: Paleontological Study of the Ryukyu Islands-VII. ''Mem. Fac. Sci. Kyushu Univ., ser.D, Geology, 24''(3), 179–188</ref>
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===Tomuru Formation===
The Tomuru Formation is distributed in the [[Iriomote Island|Iriomote]] and [[Ishigaki Island|Ishigaki]] Islands of the Yaeyama Islands, Southern Ryukyu.<ref name=":5" /><ref name=":14">{{cite journal |last1=Nishimura
===Fusaki Formation===
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