Gravity exploration is one of the most commonly used geophysical exploration methods, and it is widely used in the field of mineral resources’ exploration and engineering survey benefited from its advantages of large exploration depth, economy, and high efficiency. Gravity and its gradient data reflect the different distribution characteristics of subsurface anomalous objects, and therefore, the single data inversion cannot achieve an accurate identification for the underground objects and suffer from stronger nonuniqueness problems. To accurately identify the location and distribution characteristics of subsurface objects, we first construct models to perform separate inversions of gravity and gravity gradient data, analyze the identification ability of different anomaly components, and then innovatively introduce a cross-gradient function for the joint inversion of two gravity tensor data, ${V}_{ {xx}}$ and ${V}_{ {yy}}$ . The results show that the method combines the advantages of these two components and reflects the horizontal position of the targeted bodies more accurately; meanwhile, the portrayal of the boundary is also closer to the real model. Finally, we apply the above method to the Vinton Dome, and the inversion results recover the accurate spatial location of the Vinton Dome. The practical application results show that the joint cross-gradient inversion of gravity and gravity gradient data is more efficient for spatial location trapping and boundary inscription of subsurface targeted bodies compared with the inversion of individual component.

It is of great significance to construct a three-dimensional underground velocity model for the study of geodynamics and tectonic evolution. Southeast Asia has attracted much attention due to its complex structural features. In this paper, we collected relative travel time residuals data for 394 stations distributed in Southeast Asia from 2006 to 2019, and 14,011 seismic events were obtained. Then, teleseismic tomography was applied by using relative travel time residuals data to invert the velocity where the fast marching method (FMM) and subspace method were used for every iteration. A novel 3D P-wave velocity model beneath Southeast Asia down to 720 km was obtained using this approach. The tomographic results suggest that the southeastern Tibetan Plateau, the Philippines, Sumatra, and Java, and the deep part of Borneo exhibit high velocity anomalies, while low velocity anomalies were found in the deep part of the South China Sea (SCS) basin and in the shallow part of Borneo and areas near the subduction zone. High velocity anomalies can be correlated to subduction plates and stable land masses, while low velocity anomalies can be correlated to island arcs and upwelling of mantle material caused by subduction plates. We found a southward subducting high velocity body in the Nansha Trough, which was presumed to be a remnant of the subduction of the Dangerous Grounds into Borneo. It is further inferred that the Nansha Trough and the Dangerous Grounds belong to the same tectonic unit. According to the tomographic images, a high velocity body is located in the deep underground of Indochina–Natuna Island–Borneo–Palawan, depth range from 240 km to 660 km. The location of the high velocity body is consistent with the distribution range of the ophiolite belt, so we speculate that the high velocity body is the remnant of thee Proto-South China Sea (PSCS) and Paleo-Tethys. This paper conjectures that the PSCS was the southern branch of Paleo-Tethys and the gateway between Paleo-Tethys and the Paleo-Pacific Ocean. Due to the squeeze of the Australian plate, PSCS closed from west to east in a scissor style, and was eventually extinct under Borneo.

In this paper, we present a high resolution 3-D tomographic model of the upper mantle obtained from a large number of teleseismic travel time data from the ISC in the central Philippines. There are 2921 teleseismic events and 32,224 useful relative travel time residuals picked to compute the velocity structure in the upper mantle, which was recorded by 87 receivers and satisfied the requirements of teleseismic tomography. Crustal correction was conducted to these data before inversion. The fast-marching method (FMM) and a subspace method were adopted in the forward step and inversion step, respectively. The present tomographic model clearly images steeply subducting high velocity anomalies along the Manila trench in the South China Sea (SCS), which reveals a gradual changing of the subduction angle and a gradual shallowing of the subduction depth from the north to the south. It is speculated that the change in its subduction depth and angle indicates the cessation of the SCS spreading from the north to the south, which also implies that the northern part of the SCS opened earlier than the southern part. Subduction of the Philippine Sea (PS) plate is exhibited between 14° N and 9° N, with its subduction direction changing from westward to eastward near 13° N. In the range of 11° N–9° N, the subduction of the Sulu Sea (SS) lies on the west side of PS plate. It is notable that obvious high velocity anomalies are imaged in the mantle transition zone (MTZ) between 14° N and 9° N, which are identified as the proto-SCS (PSCS) slabs and paleo-Pacific (PP) plate. It extends the location of the paleo-suture of PSCS-PP eastward from Borneo to the Philippines, which should be considered in studying the mechanism of the SCS and the tectonic evolution in SE Asia.

Myanmar and its surrounding areas have complex topography and strong tectonic movement, which has always been a challenge to most geoscientists. We used teleseismic tomography to study the subsurface velocity structure in this area. We present a new P-wave tomographic model beneath Myanmar and the surrounding areas by inverting 129,788 arrival-time data recorded by 372 stations. We found an inclined high-velocity subducting plate beneath central Myanmar, where the dip angle becomes smaller near 25°~26°N, and the seismic depth is limited below 200 km. The Indian oceanic lithosphere is being detached from the Indian continental lithosphere, which limits the depth of the earthquake. The active Tengchong volcano is underlain by a prominent low-velocity (low-V) anomaly in the shallow mantle, which may be caused by the subduction and dehydration of the Burma microplate (or Indian plate). The formation of the Singu volcano is related to the mantle flow of the Qinghai–Tibet plateau and the tearing of the Indian plate. The Yangtze craton (beneath the Sichuan Basin) shows a high-velocity anomaly, and both the shallow and deep parts have been destroyed, which may be related to the upwelling of deep heat flow.

High-precision gravity observation is key to studying Earth’s gravity field, which reflects matter distribution and movement of matter within the Earth’s interior, on its surface, and in outer space. Compared to traditional mobile observations, continuous gravity array observations can effectively improve both accuracy and temporal resolution. The China Earthquake Administration has deployed a total of 115 continuous gravimeters, including superconducting gravimeters (SG), atom gravimeters (AG), and spring gravimeters, preliminarily establishing a continuous gravity observation network. However, the accuracy differences among different types of instruments constrain the comprehensive application of the data. To address this, it is imperative to conduct research on the accuracy evaluation of various gravimeters. This study innovatively introduces the Complementary Ensemble Empirical Mode Decomposition (CEEMD) algorithm to decompose and reconstruct the measured data from continuous gravimeters, extracting the solid Earth tide signal. Subsequently, an external conformity accuracy evaluation is performed by comparing it with theoretical tidal models, thereby achieving instrument accuracy assessment. To verify the feasibility and superiority of the CEEMD algorithm, this paper first designs a combined simulation signal experiment, in which the performance of Bessel filtering, Kalman filtering, Variational Mode Decomposition (VMD), Empirical Mode Decomposition (EMD), and CEEMD in extracting tidal frequency band signals is comparatively analyzed. Finally, these methods are applied to process observational data from three gravimeters (SG, AG, and DZW relative gravimeter (DZW)) at the Yilan station, extracting the solid Earth tide signal and comparing its external conformity accuracy with theoretical models. The results show that these algorithms can effectively extract the solid Earth tide signal, with the evaluated accuracy of the three instruments consistently ranked as follows: SG > AG > DZW. However,The CEEMD method demonstrated optimal performance in the accuracy evaluation of the three gravimeters, with the following external conformity accuracies achieved: SG: 1.83 μGal, AG: 2.59 μGal, DZW: 3.83 μGal.

The subduction and disappearance process of the Proto-South China Sea is closely related to the opening of the South China Sea. Studying its subduction process and dynamic mechanism helps to explore the Cenozoic evolution model of the South China Sea. We collected teleseismic travel time data from Southeast Asia over the past 20 years, preprocessed the original data through data filtering, picking first arrival , and crustal correction, and obtained a three-dimensional velocity model of Southeast Asia using the Fast Marching Teleseismic Tomography(FMTT) method. The velocity imaging results reveal the presence of high-velocity anomalies in the mantle and mantle transition zones beneath Borneo and the Philippines. It is worth noting that the distribution range of serpentinite and serpentinite belt discovered in this area is highly consistent with the range of high-velocity anomaly bodies. Therefore, it is highly likely that the high-velocity anomalous bodies discovered in this area are remnants of the Proto-South China Sea subduction plate in the mantle transition zone. The morphology of residual subduction plates indicates that the Proto-South China Sea was subducted and closed from south to north, which may have had a certain impact on the Cenozoic seafloor spreading of the South China Sea; The detailed distribution range of residual plates further delineates the location of the disappearance of the Proto-South China Sea.