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| Nagasaki Trough | |
|---|---|
| Name | Nagasaki Trough |
| Location | East China Sea |
| Type | Submarine trough |
| Basin countries | Japan |
Nagasaki Trough is a submarine trough located off the western coast of Kyushu in the East China Sea near Nagasaki Prefecture. The trough lies within a complex marginal sea setting influenced by the Sea of Japan (East Sea), East China Sea, and continental shelves adjacent to Kyushu and Tsushima Island. Its geologic evolution reflects interactions among the Eurasian Plate, Philippine Sea Plate, and microplates associated with the Ryukyu Trench and Nankai Trough subduction systems.
The trough formed through Mesozoic to Cenozoic processes including rifting linked to the opening of the East China Sea Basin, post‑rifting thermal subsidence, and later deformation related to the Pliocene–Quaternary arc‑continent collision that reshaped the Ryukyu Arc and adjacent margins. Tectonosedimentary evidence ties stratigraphic sequences to episodes recorded in the Shimanto Belt, Oita and Saga Prefecture onshore geology, and correlations have been made with cores from the ODP and IODP drilling campaigns. Volcaniclastic contributions from eruptions related to Aso Volcano and Kirishima–Sakurajima systems influenced basin fill during the Miocene and Pleistocene.
The trough sits in a transitional zone between the Eurasian Plate passive margin and the active subduction of the Philippine Sea Plate beneath the Eurasian Plate along structures related to the Ryukyu Trench and the Nankai Trough. Interaction with the Yangtze Craton and back‑arc processes associated with the Izu–Bonin–Mariana Arc have been proposed, while microplate boundaries near Amami Ōshima and Tokara Strait influence strain partitioning. Seismic tomography and GPS campaigns by institutions such as Japan Meteorological Agency and Geological Survey of Japan document crustal deformation, slab geometry, and mantle flow beneath the marginal sea.
The trough exhibits a narrow, elongate bathymetric depression flanked by submarine ridges, terraces, and submarine canyons draining coastal catchments around Nagasaki Prefecture, Hirado Island, and the Genkai Sea. Multibeam surveys conducted by the Japan Agency for Marine‑Earth Science and Technology reveal steep escarpments, sediment waves, and depositional fans connected to channels feeding the East China Sea continental slope. Nearby geomorphic features include the Tsushima Basin, Noto Basin, and isolated seamounts related to Cenozoic volcanism.
Sediment fill in the trough comprises hemipelagic muds, turbidites, and shelf‑derived sands sourced from rivers such as the Chikugo River and influenced by episodes of sea‑level change during the Last Glacial Maximum and interglacials. Seismic reflection profiles show stacked clinoforms, contoured drift deposits, and mass‑transport deposits comparable to sequences studied in cores from the Continental Shelf and Aegean Sea analogs. Biostratigraphy using microfossils tied to Foraminifera and Radiolaria assemblages, and magnetostratigraphy correlated with the Brunhes–Matuyama reversal, provide age control for depositional units.
The trough region is seismically active with recorded earthquakes attributed to oblique convergence, strike‑slip faults, and thrusting along buried faults linked to the Ryukyu‑Nankai system; notable institutions monitoring seismicity include the Japan Meteorological Agency, National Research Institute for Earth Science and Disaster Resilience, and United States Geological Survey. Historical tsunamigenic events affecting Nagasaki and Kyushu coastlines have been linked to offshore earthquake sources, submarine landslides, and paleo‑seismic records preserved in turbidites; tsunami hazard models used by the Ministry of Land, Infrastructure, Transport and Tourism incorporate these scenarios for evacuation planning.
The trough and surrounding seas host productive habitats supporting fisheries targeting Japanese amberjack, Pacific saury, and demersal species exploited by fleets from Japan and neighboring regions; important ports include Nagasaki (city), Sasebo, and Hirado. Upwelling and shelf break dynamics influence plankton blooms hosting diatoms and copepods, which support higher trophic levels including squid and tuna. Benthic communities on soft‑sediment plains include echinoderms and mollusks studied by researchers at Kyushu University and Nagasaki University. Potential mineral resources such as gas hydrates and phosphate‑rich sediments have been investigated in conjunction with energy agencies and companies like Japan Oil, Gas and Metals National Corporation.
Exploration history spans Japanese coastal surveying in the Meiji era, postwar hydrographic work by the Hydrographic and Oceanographic Department of the Japan Maritime Self-Defense Force, and modern marine geology expeditions by JAMSTEC, University of Tokyo (Ocean Research Institute), and international partners through IODP and collaborative cruises with institutions like WHOI and GEOMAR. Key publications in journals such as Journal of Geophysical Research, Marine Geology, and Quaternary Research document stratigraphy, tectonics, and hazard assessments. Ongoing multidisciplinary programs integrate seismic reflection, multibeam mapping, piston coring, and remotely operated vehicle surveys to refine understanding of the trough's evolution.
Category:Geography of Nagasaki Prefecture Category:Oceanography of Japan