11:15 AM - 11:30 AM
[SCG52-13] Geological structure and tectonics of the northern slope area of East China Sea
Keywords:East China Sea, Okinawa Trough
In the context of the structural evolution of the Okinawa Trough (OT), the OT and the adjacent regions are usually considered to be divided into three segments; northern, central, and southern, by the Tokara Valley and the Kerama Gap, respectively [1]. Although the structural evolution of the central and southern OT is well discussed based on various scales of seismic refraction and reflection survey data by studies such as Arai et al. (2017) [2], the northern OT is not well studied enough. A bathymetric feature elongating southward from the Daiichi-Danjo Knoll and the Daini-Danjo Knoll, tentatively called the “Oki-Danjo Hills”, is located on the western slope area of the northern OT. Although this feature is important in the aspect of its bathymetric characteristics and its location to reveal the structural geological history of the northern OT, only a few previous works or surveys have mentioned about this feature.
In this study, we conducted high-resolution seismic reflection surveys and interpreted the seismic structures of hundreds-meter-depth under the sea floor of the Oki-Danjo Hills. For data acquisition, we used the mini-GI gun and the multi-channel streamer, and some of these seismic data were preprocessed using method such as deconvolution before the analyses.
The seismic reflection data show some distinctive unconformities and faults correlating to the bathymetric characteristics. Discontinuities of the unconformities in some survey lines due to fault displacement can also be identified by using bypassed survey lines. Our results imply that some layers filling the basin beside the Oki-Danjo Hills do not accumulate on the top of the hills, and we can discuss the tectonic sequence of faulting and depositions.
Furthermore, the spatial distribution of the faults and sediments may indicate that the Oki-Danjo Hills is the blocks complexly formed by normal faults that created half grabens and other subsequent faulting events.
These events can be compared to the advocated theory of the tectonic evolution of the northern Okinawa Trough based on the distribution of two types of faults [3], and we may be able to more widely explain the structural geological history of the northern Okinawa Trough and the adjacent regions. If we can obtain additional information such as ages from borehole samples, such information can provide stronger constraints on the structural geological history.
References: [1] Tokuyama et al. (2001) Journal of the Japan Society for Marine Surveys and Technology 13, 27-53. [2] Arai et al. (2017) Journal of Geophysical Research: Solid Earth 122, 622-641. [3] Oiwane et al. (2007) Journal of the Sedimentological Society of Japan 64, 137-141.
In this study, we conducted high-resolution seismic reflection surveys and interpreted the seismic structures of hundreds-meter-depth under the sea floor of the Oki-Danjo Hills. For data acquisition, we used the mini-GI gun and the multi-channel streamer, and some of these seismic data were preprocessed using method such as deconvolution before the analyses.
The seismic reflection data show some distinctive unconformities and faults correlating to the bathymetric characteristics. Discontinuities of the unconformities in some survey lines due to fault displacement can also be identified by using bypassed survey lines. Our results imply that some layers filling the basin beside the Oki-Danjo Hills do not accumulate on the top of the hills, and we can discuss the tectonic sequence of faulting and depositions.
Furthermore, the spatial distribution of the faults and sediments may indicate that the Oki-Danjo Hills is the blocks complexly formed by normal faults that created half grabens and other subsequent faulting events.
These events can be compared to the advocated theory of the tectonic evolution of the northern Okinawa Trough based on the distribution of two types of faults [3], and we may be able to more widely explain the structural geological history of the northern Okinawa Trough and the adjacent regions. If we can obtain additional information such as ages from borehole samples, such information can provide stronger constraints on the structural geological history.
References: [1] Tokuyama et al. (2001) Journal of the Japan Society for Marine Surveys and Technology 13, 27-53. [2] Arai et al. (2017) Journal of Geophysical Research: Solid Earth 122, 622-641. [3] Oiwane et al. (2007) Journal of the Sedimentological Society of Japan 64, 137-141.