To address the demand for high-precision exploration of natural gas hydrates in the northern South China Sea, this paper presents a novel high-precision small-scale 3D seismic exploration technology. The research team independently developed a seismic acquisition system, incorporating innovative designs such as a narrow trace spacing of 3.125 m and a short streamer length of 150 m. By integrating advanced processing techniques, including pre-stack noise suppression, spectral broadening, and refined velocity analysis, the system significantly enhances the precision and spatial resolution of shallow seismic data. During field trials in the Qiongdongnan basin, the system successfully acquired 3D seismic data over an area of 50 km², enabling fine-scale imaging of sub-seabed strata within the upper 300 m. This represents a notable improvement in resolution compared to conventional 3D seismic technologies. When benchmarked against international counterparts such as P-cable, our system demonstrates distinct advantages in terms of exploration depth (reaching 1800 m) and dominant frequency range (spanning 10~390 Hz). The research findings provide a reliable technical approach for the detailed characterization of natural gas hydrates and the inversion of reservoir parameters, thereby holding significant practical value for advancing the industrial development of natural gas hydrates in China’s offshore areas.

The Beibu Gulf and its surroundings are a significant intraplate seismic zone in the northwest of the South China Sea. At least 15 M>5 earthquakes and 4 M>6 events have occurred historically. In 1605, a destructive earthquake with M7.5 occurred in the southern Beibu Gulf, causing villages to submerge into the sea with an area exceeding 100 km2 of land subsidence into the sea. This seismic zone has serious earthquake risk, but few studies focused on the moderate to strong earthquake sequence in this area, leading to unclear seismic structures, mechanisms, and triggers of earthquakes in the region. In this work, waveform data of the 2023 Beibu Gulf earthquake sequence (ML5.4) are well analyzed based on 4-month data recorded at 51 broadband stations. One foreshock and 73 aftershocks were detected by template matching techniques. The entire earthquake sequence is relocated using the HypoDD relocation method and the focal mechanism solutions of 12 M>1.5 earthquakes are inverted. The results show that the 2023 Beibu Gulf earthquake sequence forms a belt in the NWW-SEE direction, with a lateral extent of ~5.0 km and a width of ~1.5 km. Vertical slices show that the earthquake sequence is distributed continuously and densely with a dip angle of about 50° toward the NNE direction. Most foreshocks and aftershocks have similar source mechanisms to the main shock including the NWW-trending fault plane having a strike of 288°, a dip angle of 51°, and a slip angle of 177°. The location and attitude of the seismic fault match well with the NWW-trending Wei-2 Fault (F1) identified by petroleum exploration. The stereographic projection of the P-axes indicates that the principal compressive stress direction is NW-SE in the source area, which intersects obliquely with the F1, resulting in the right-lateral strike-slip faulting of the 2023 Beibu Gulf earthquake sequence. The seismic images in the research area show that the location of the 2023 Beibu Gulf earthquake sequence corresponds well to the deep columnar low-velocity zone, indicating that the triggering of the event may be related to the magmatic-hydrothermal fluids produced by the Hainan mantle plume. By comparing the seismic activity characteristics of the surrounding areas, and combining geological with geophysical survey information, we believe that deep hydrothermal fluids and fault structures or weak zones are the main driving factors of seismicity in this area.

Shallow subsurface structure detection in coastal zones serves as a critical foundation for resource development and engineering construction. However, conventional geophysical methods exhibit significant limitations in land–sea transition zones, where pronounced “boundary effects” create substantial “exploration gaps” due to difficulties in merging terrestrial and marine datasets. To achieve truly seamless subsurface imaging across the coastal boundary, this study develops and implements an integrated cross-boundary survey approach utilizing nodal seismometers and seismic ambient noise. At Dong’ao Island, Zhuhai, we deployed a comprehensive seismic profile spanning hillside, sandbeach, and seafloor environments to evaluate the method’s applicability in complex coastal settings systematically. Results demonstrate substantially stronger ambient noise energy in submarine environments compared to terrestrial settings. All stations recorded abundant and stable high-frequency (>1 Hz) noise signals, which are adequate for shallow subsurface imaging. Rayleigh wave dispersion curves extracted via the advanced Frequency-Bessel transform method enabled inversion of a continuous 2D shear-wave velocity profile along the survey line. Bedrock interface depths determined using the Horizontal-to-Vertical Spectral Ratio (HVSR) method showed remarkable consistency with the bedrock morphology revealed by the shear-wave velocity structure, validating the reliability of our approach in coastal environments. This research successfully demonstrates the feasibility of seismic ambient noise imaging as a bridging technique for land–sea exploration, providing an efficient, environmentally friendly, and continuous technical solution to overcome coastal zone exploration challenges.

The geodynamics and plate tectonics of the South China Sea (SCS)-Taiwan region since Miocene times are uncertain because the former extent and tectonic configuration of the subducted easternmost SCS along the Manila trench is uncertain. Here we unravel the regional kinematic context from main offshore constraints including published unfolding of the Manila slab from seismic tomography, which provides insight on restoring the subducted part of the SCS. We reconstruct a whole northern SCS continent-ocean boundary (COB) that consists of a northeastern SCS COB segment (called ‘S3’), trending N070° that roughly parallels the present SCS shelf; a 350-km long ~N-S trending segment S2 that steps north to Hualien; and, a third segment S1 that extends from east of Hualien beneath the Ryukyu subduction zone trending N085° that ends near Miyako Island in the Ryukyus.We demonstrated that the two-plate kinematic model is the best framework to explain the existing data. The boundary between Eurasia and Philippine Sea plate is a ~NS oriented left-lateral lithospheric shear fault called the Manila transcurrent fault (MTF). The MTF initiated ~18 Ma at the onset of the tear and progressively moved eastward, creating the intra-oceanic Luzon arc. The MTF ancestor was a N337° oriented left-lateral shear fault, while the HB-PSP/EU motion was changing to N307°, allowing the HB-PSP plate to subduct between the two lips of a westward propagating tear fault until ~7 Ma. Since ~7 Ma, the MTF-PFZ constantly moved westward and 23° clockwise rotated from N337° to ~NS, which began collision ~7 Ma ago along the EU margin. Plate kinematic reconstructions from ~18 Ma to Present are synthesized in terms of continental or oceanic nature of the main PSP-HB and EU entities before their subduction that provide new understanding on Taiwan, PSP-SCS kinematics, and regional histories. This work is supported by Key projects of the Chinese National Natural Science Foundation (contracts 91958212, 42106078).

The coastal zone, a critical interface between land and sea, is characterized by intense human activity and development, making it a key area for multidisciplinary research. However, achieving accurate shallow subsurface detection in these areas, including nearshore waters, remains challenging due to limitations in current exploration technologies and the distinct challenges of marine and land-based survey methods. This study tackles this issue by investigating the western coastline of Dong'ao Island, Zhuhai. A network of 22 node seismograph stations were deployed across varied coastal environments—hillside, beach, and seafloor—to systematically analyze seismic ambient noise characteristics in each setting. The research aims to enhance understanding of seismic noise in different coastal contexts, contributing to improved techniques for shallow subsurface detection in coastal zones. Key findings from the analysis can be summarized as follows:Submarine stations exhibit higher seismic ambient noise energy levels compared to their hillside and beach counterparts. Dominant frequency bands concentrate within the ranges of 2~10 s and 0.5~0.01 s. Sources of this noise are primarily attributed to mechanical disturbances originating from coastal and offshore maritime activities, alongside anthropogenic influences such as nearby human activities and road traffic. High-frequency seismic background noise greater than 1 Hz in the three environments is rich in information and balanced in signal, which meets the needs of shallow strata imaging in coastal zones. Employing F-K inversion techniques, a two-dimensional shear wave velocity profile was successfully generated for the study area, delineating the depth of the basement interface beneath the sedimentary layer. The viability of utilizing ambient noise for probing coastal zones was substantiated via comparison with results obtained from the horizontal-to-vertical spectral ratio (HVSR) method and corroborated by adjacent drilling data. This outcome underscores the potential of passive seismic methodologies for investigating complex coastal geophysical structures. To derive high-order mode dispersion curves characterized by energy concentration, comparative experiments were conducted with varying operational parameters for data acquisition. Subsequently, a joint inversion of both high-order and low-order modes was performed, yielding higher-resolution and more accurate velocity structure imaging results beneath the coastal zone. The successful acquisition of two-dimensional shallow shear wave velocity profiles in the western coastal zone of Dong'ao Island unequivocally validates the feasibility of employing passive source node seismograph exploration technology to eliminate blind spots in shallow strata exploration within coastal zones. This approach transcends the limitations imposed by traditional exploration techniques, achieving seamless integration of land-to-sea seismic exploration. It is anticipated that this research will furnish robust technical support for engineering projects and resource development initiatives in coastal regions. This research was granted by the National Natural Science Foundation of China (No. 42106078) and the Guangzhou Science and Technology Plan Project (No. 2023A04J0243).