Evidence of an active rift zone in the northern Okinawa Trough

Minami, Hiroki; Okada, Chiaki; Saito, Keita; Ohara, Yasuhiko

doi:10.1016/j.margeo.2021.106666

Cited by 7 publications

(1 citation statement)

References 68 publications

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“…The width of the Okinawa Trough increases from 60 to 100 km in the south to 230 km in the north, while the water depth decreases from 2,300 m to 200 m from south to north (Sibuet et al, 1987;Sibuet et al, 1998;Tsai et al, 2021). The crust and sedimentary layers become gradually thinner along the length of the trough, from 20 to 30 km in the north to 10-12 km in the south (Minami et al, 2022). The northern Okinawa Trough is composed of numerous half-grabens covered by thick terrigenous material layers up to 8 km thick from China's Yangtze and Yellow rivers, whereas the southern Okinawa Trough has a sedimentary cover of up to 2 km.…”

Section: Geological Backgroundmentioning

confidence: 98%

Geophysical evidence for submarine methane seepage on the Western slope of Okinawa Trough

Luo

Cai

et al. 2022

Front. Earth Sci.

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Identifying seafloor methane seepage efficiently has important implications for assessing environmental impact, reducing the uncertainty of top seal integrity, understanding the petroleum system, and mitigating the drilling hazards due to shallow gas influx. Pore water geochemistry analyses suggest that the study area has an extremely high methane seepage flux and active methane anaerobic oxidation processes. However, geochemical data cannot provide details about the internal seepages. The geophysical dataset from the Western slope of Okinawa Trough, including 2D high-resolution seismic, sub-bottom profiles, and bathymetry, gives us a good opportunity to understand the detailed characteristics of methane seepages in this study. Geophysical data have revealed numerous methane seepage-related features such as seismic chimneys, pockmarks, submarine domes, and amplitude anomalies, including bright spots and enhanced reflections. Pockmarks and domes are often associated with seismic chimneys, indicating that fluid migration is important in their formation. The various geophysical expressions may represent different stages of methane seepage. Fluid quickly drains, causing severe sediment deformation and forming pockmarks, whereas domes may indicate the early stages of fluid discharge. Chimneys that do not extend to the seafloor may indicate that the venting is gradual and focused. Flares linked to domes or pockmarks may indicate that the fluid migration is active. Several factors triggered the existence of methane seepages on the Western slope of the Okinawa Trough, including tectonic setting, overpressure and rapid sedimentation.

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