OBS973-1 is a wide angle reflection and refraction deep seismic line using Ocean Bottom Seismometers (OBS), collected for the first time in the southern part of South China Sea. The line crosses the southern margin of the Southwest Sub-basin and the middle part of Nansha Block. By seismic phase analysing and travel time fitting, a 2D P-wave velocity model along the line is constructed. The modeling results show that the surface sedimentary layer has a velocity of 2.5∼4.5 km/s and a thickness of 1000∼3000 m, with locally rough basement interface. The crystalline basement has a velocity of 4.5∼5.5 km/s on the top, increasing to 6.8∼6.9 km/s near the bottom of the crust. In the middle crust there is a small velocity discontinuity (0.1∼0.2 km/s), while the Moho on the bottom crust has a large velocity contrast (1.2 km/s). In the top mantle the velocity is 8.0∼8.1 km/s. The Moho depth and the crustal thickness have much difference between the northern and southern segments along the line. The northern segment is in the deep sea basin, where the Moho is 11 km deep and the crystalline crust is only 5∼6 km thick, which are typical characteristics of oceanic crust. In contrast, the southern segment is on the continental block, where the Moho has a maximum depth of 24 km and the crust has a corresponding thickness of 20 km, which are representative characteristics of thinned continental crust. From the deep sea basin to the continental block, the Moho depth and the crustal thickness increase rapidly. In the continental area, the upper crust and lower crust have similar thickness and variation. No High Velocity Layer (HVL) is seen in the lower crust. These may imply that pure-shear extension and uniform thinning are dominating inside the crust, and magma underplating is not developed in the lower crust. Comparing with the structure models of OBS973-2 and OBS973-3, it is inferred that the middle and eastern parts of Nansha Block have similar tectonic characters, and the two sides of Southwest Sub-basin are a pair of non-volcanic asymmetric conjugate continental margins.
Processing and analysis of ocean bottom seismometer (OBS) data are of great importance to obtain the deep crustal structure. The deep seismic profile OBS2006‐2 was carried out in 2006 along the extinct spreading ridge of the northwest sub‐basin of the South China Sea. This survey is successful to provide high quality data whose seismic signals can be observed at the offset up to 120 km, but 2 OBSs’ recording data (OBS03 and OBS06) cannot be read correctly and were not used in later structure modeling. However, OBS data are very precious due to the high cost and arduous work. The price is more expensive when encountering severe weather during a survey. This paper is focused on reprocessing of these 2 OBSs’ data by use of the methods of checking data format, comparing signals with adjacent OBSs and resampling the data. Finally we acquire these 2 OBSs’ seismic record sections in which abundant seismic phases are clearly seen. We also obtain the seismic record section of OBS03 along the profile OBS973‐3 in the Nansha Island using the same methods above. The instrument OBS06 along the profile OBS2006‐2 and the instrument OBS03 along the profile OBS973‐3 are the same instrument confirmed by checking their logs recorded in 2006 and 2011, respectively. It demonstrates that the processing method for abnormal OBS data is reliable and effective. Then the ray‐tracing and travel‐time simulation were carried out for OBS06 and OBS03 using the interactive trial‐and‐error 2D ray‐tracing method based on the previous P‐wave velocity model of OBS2006‐2. The input of new travel‐time picks should provide stricter constraints for the deep structure beneath the profile OBS2006‐2. This research on abnormal data reprocessing does not only improve the reliability and resolution of the crustal structure, but also provide valuable experiences for OBS processing for other study areas in the future.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.