Edge detection represents a critical task in potential field data interpretation and is extensively utilized for detecting faults, contacts, and other linear geological structures. However, conventional methods are constrained by several limitations, including inadequate balancing of signals with varying amplitude intensities, dispersed detection results, and insufficient suppression of spurious signals. To overcome these challenges, we propose an improved edge detection method, designated as the hyperbolic tangent (TANH) function with Gaussian envelope constraints on the total gradient modulus tilt angle (THASTG). The THASTG method is formally defined as a tilt angle approach based on the total gradient modulus, incorporating dual constraints through a Gaussian envelope and a TANH function. We initially conducted comparative analyses between the THASTG and established methods by using complex models simulating three distinct geological scenarios, thereby validating the feasibility of the methodology. Subsequent application to real gravity data from the South China Sea region demonstrated that compared with conventional techniques, THASTG yields enhanced structural detail, improved boundary resolution, and superior noise suppression. This method effectively suppresses noise interference and successfully avoids the introduction of spurious boundaries while maintaining consistency with previously documented major tectonic features. This study provides high-resolution structural constraints for the South China Sea region, delineates the offshore extension of the Red River Fault system, and accurately maps the continent–ocean boundary configuration. Our results demonstrate that the proposed methodology provides an effective tool for precise structural characterization and in-depth analysis of geodynamic evolution processes.

Understanding rupture transfer across fault junctions is critical for interpreting complex multi-fault earthquakes. For the 2023 M_w 7.8 Kahramanmaraş event, we construct three dynamic rupture models constrained by surface fault traces, relocated aftershocks, kinematic slip inversions, near-field strong-motion records, and GPS data to distinguish among potential nucleation sites along the East Anatolian Fault (EAF). Our simulations reveal that although the final slip distributions are insensitive to the precise nucleation point owing to complex fault geometry, the dynamic conditions required for rupture initiation on the EAF differ significantly. Nucleation at the triple junction is facilitated by dynamic Coulomb stress triggering from the Narlı branch fault. Although the supershear rupture velocity is different along the Narlı branch fault of Model 1 and Model 3, both models support nucleation at the triple junction. In contrast, nucleation at 9 km southwest of the triple junction requires artificial stress concentrations, as shown in Model 2. Model 3 shares the same stress concentration along the EAF; however, its near-P-wave supershear speed along the branch fault narrows the Mach cone and directly impedes nucleation to the southwest. All the models show good correspondence with the near-field seismogram and GPS observations. Additionally, we compare the source time functions of the three models with the U.S. Geological Survey result, which imply that the near-P-wave supershear speed along the branch fault is less likely. Our results suggest the triple junction is the most likely nucleation site, and although the 9 km southwest of the triple junction is still possible, it requires highly localized initial stress concentrations.

In this study, we investigate the source and dynamics of a mesoscale gravity wave (MGW) observed over northern China. On January 12, 2010, an OH airglow imager at the Xinglong station (40.2°N, 117.4°E) detected an MGW propagating from southwest to northeast, consistent with the background wind direction. The wave exhibited a horizontal wavelength of 125 ± 7.6 km, an observed period of 25 ± 3.2 min, and a phase speed of 83 ± 12.4 m/s. The momentum flux and the energy flux of the MGW were approximately 24.93 m²/s² and 1.08 × 10⁻⁵ W/m², respectively, from the airglow imaging observation. During propagation, wave breaking generated secondary ripples with wavelengths of 5–12 km. These ripples were likely caused by wind shear, as measured by the Doppler meteor radar at Shisanling (40.3°N, 116.2°E). According to OH emission profiles from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on board the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, the height of the OH airglow layer was ~81 km during the MGW propagation event. A separate northwestward-propagating small-scale gravity wave with a wavelength of ~35 km was also observed. The backward ray-tracing analysis conducted with European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis data indicated that the jet system near the Tibetan Plateau served as the source for the MGW.

As a planet lacking a global magnetic field, Mars interacts directly with the solar wind, forming an induced magnetosphere that mediates energy transfer and atmospheric ion loss. The topology of this interaction and the resulting atmospheric ion escape are strongly influenced by the orientation of the interplanetary magnetic field (IMF). In this study, we utilize a hybrid model to investigate how variations in the IMF orientation shape ion current systems and atmospheric ion escape rates of O⁺, O₂⁺, CO₂⁺. We first perform simulations with a constant |B_sw|, where varying the IMF cone angle results in different strengths of the convective electric field (E_sw = V_sw × B_sw). Our results suggest that the spatial morphology of ion plumes undergoes a substantial evolution, forming a distinct cross-flow plume as the IMF rotates from perpendicular to parallel. These ion plumes exhibit a mass-dependent deflection, where heavier CO₂⁺ travel farther with larger gyroradii than lighter O⁺, acting as an asymmetric obstacle in the –Y_MSE hemisphere (where MSE is the Mars solar electric coordinate frame). In turn, the solar wind proton current develops pronounced asymmetries under a parallel IMF, becoming largely diffused in the −Y_MSE hemisphere because of the interaction with the additional plume obstacles. Consequently, the ion escape rates exhibit a nonmonotonic dependence on the IMF orientation, peaking under a parallel  IMF as escape shifts from a tail- to plume-dominated flow with substantial upstream enhancement. To decouple the effects of IMF geometry from those of the convective electric field, we further conduct a comparative simulation with constant  B_y  (hence constant |E_sw|), where the cone angle is varied by changing the B_x component while allowing |B_sw| to vary. With increasing B_x toward a parallel orientation, the total field magnitude grows, causing the Alfvén Mach number (M_A) to decrease from super-Alfvénic to trans-Alfvénic and ultimately to sub-Alfvénic values. Within the range from perpendicular to a 30° cone angle, where the system remains in the super-Alfvénic regime, ion escape is largely insensitive to the growing B_x component. This finding indicates that the magnetic barrier maintains its shielding efficiency under the super-Alfvénic regime.