Overview of the seismic survey and dredge sampling in the vicinity of the Tokara Islands conducted during geological map research cruises in 2021

<p>Multichannel seismic survey and dredge sampling were conducted near the Tokara Islands, northwest of the northern Okinawa Trough during GB21-2, GB21-3, and GS21 cruises with the aim of constructing marine geological maps at a 1:200,000 scale. We present an overview of the seismic survey and dredge sampling results, and report characteristic geological structures along the observed seismic profiles. Seismic profiles east of the Tokara Islands reveal a sedimentary basin overlaying the acoustic basement. Within this basin, numerous WNW–ESE-trending normal faults are developed, particularly in the northern and southern sectors. We recognized an unconformity that reflects a few stages of tectonic movements during the formation of the sedimentary basin. Dredging from a lower unit outcrop yielded sedimentary rocks. Seismic profiles west of the Tokara Islands reveal a normal fault that extends almost 50 km along the western margin of a topographic high, cutting through strata and dipping to the west. In this region, the flat seafloor surrounding the topographic high displays widespread NNE–SSW trending normal faults, while ENE–WSW trending faults are exclusively found west of the nSuwanosejima Island and Akusekijima Island. Additionally, normal faults, potentially with strike-slip components, are densely concentrated in the southwestern part of the topographic high. We aim to proceed with the construction of seismic stratigraphy and the interpretation of structural history after the conclusion of all planned research cruises in the vicinity of the Tokara Islands. These results will provide further insights into the tectonic evolution of the northern Okinawa Trough and the surrounding region of the Tokara Islands.</p>