Based on magnetotelluric array data and the three‐dimensional (3D) inversion algorithm, we obtain the 3D electrical structure of the 1976 Ms7.8 Tangshan earthquake zone. The seismogenic structure comprised a thick resistive anomaly located east of the Tangshan fault (TSF), a thin resistive belt extending westward, and the TSF zone. A geodynamic model is proposed based on the 3D electrical model and the other research findings. The model indicates that the primary cause of the Tangshan earthquake was the almost EW‐trending horizontal pushing from the west. The local uplift of deep thermal materials on the west side of TSF produces tensile deformation superimposed on the existing shear deformation. The combined effect of these two forces controls the Tangshan earthquake deformation characteristic. Prevailing horizontal pushing from the west and local uplift of hot material may be associated with the Tibet Plateau's eastward escape and the subduction of the Pacific plate.

SUMMARY: Marine magnetotelluric (MT) and controlled source electromagnetic (CSEM) methods have been routinely applied to survey the crustal and upper mantle electrical resistivity structures beneath the sea floor. In practice, there are inevitably site gaps and contamination by noises in the collected data because of lost ocean bottom electromagnetic receivers, unusable data, and difficulties in deploying instruments near deep trenches. So far, it remains unclear to what degree those factors will lower the resolution and the credibility of marine MT and CSEM inversion models. In this paper, we investigate the individual and combined effects of site gaps and data noises on the inversion models through synthetic analyses based on a simple block resistivity model and a realistic resistivity structure derived from the Mariana Trench. The results suggest that data with a sufficiently high signal-to-noise ratio can reasonably recover the subseafloor structures in the area of data gap. The transverse electric mode and tipper data from the MT method are much more sensitive to the structure near the site gap. The joint inversion of MT and CSEM data would improve the model's resolution at the site gap area. The inversion of data with a relatively low signal-to-noise ratio, for example, 10 per cent, can recover the structures with few artefacts if there is no site gap. But if the site gap and noisy data are combined, even a joint inversion cannot correctly recover the burial depths and geometries of the anomalous bodies beneath the site gap where vertical strips are likely present. To improve the model's resolution and suppress inversion artefacts, we propose constraining part of the model with as much a prior information as possible. Specifically, for a survey in the subduction zone, we could reduce the penalties on the model's smoothness at the upper and low interfaces of the resistive subduction slab, or even fix the resistivity of the resistive slab with the help of other information, if any. The inversion models shown in this paper provide valuable references for the site design before marine MT and CSEM surveys as well as for interpreting real data inversion models that may be subject to the same biases introduced by the site gap and noise.

Antarctica is covered by a thick ice sheet, and the application of geophysical methods is necessary to image the subglacial structures for studying the hydrologic systems and tectonic deformations in the Antarctic continent. The magnetotelluric (MT) method is one of the best approaches to obtain the subglacial electrical resistivities. However, only a very small volume of data has been collected so far in Antarctica using this method. In this paper, we report on a broadband MT profile collected at 10 sites in the south of the Chinese Zhongshan Station at Prydz Bay, and a 3D resistivity model was constructed by inversion of these data. This 3D model shows two low resistivity zones at a depth shallower than 6 km. They are consistent with the low-velocity zones in the previous shear-wave model and can be interpreted as the result of interconnected fluids associated with a downward migration of subglacial water. In addition, a distinct eastward dipping low resistivity zoneis present in the crust, which extends from the top surface to the lower crust. Since its location coincides with the highly positive magnetization named Amery Lineament, it is proposed that this eastward dipping low resistivity zoneextending in the entire crust probably reveals the geometry structure of the Amery Lineament at depth. Besides, it can be inferred from this new 3D resistivity model that the Amery Lineament is at least a crustal-scale structure, which probably outcrops on the land surface but was covered by the ice sheets in the study area.

Arc magmatism serves as a key archive of subduction dynamics, yet the dynamic mechanisms that drive the compositional evolution and eventual cessation of long-lived arc magmatism remains insufficiently understood. The Antarctic Peninsula preserves a unique, progressive south-to-north cessation of arc magmatism, thus offering a natural laboratory to address this issue. Although ridge-trench collision could explain the termination in the south, the geodynamic drivers for the final arc demise in the north (represented by South Shetland Islands) remain elusive. Here, we present new geochronological and geochemical data for Cenozoic basalts and basaltic andesites from the South Shetland Islands (SSI), and integrate them with regional datasets to track the mantle-source evolution and the mechanisms responsible for its shutdown. The 40Ar/39Ar dating for feldspar grains from one representative basalt sample near the Great Wall Station yielded a well-defined plateau age of 30.56 ± 0.45 Ma. The studied rocks exhibit variable SiO2 (46.0–56.9 wt.%) and K2O (0.23–1.40 wt.%) contents and can be classified as basalt and basaltic andesite. Overall, the samples display relatively low 87Sr/86Sr (0.70335–0.70418) and high 143Nd/144Nd (0.51293–0.51301) ratios, which, together with typical arc-like trace element signatures (e.g., Ba/Nb = 60–210, Th/Nb = 0.76–2.69), indicate derivation from a depleted mantle metasomatized by slab fluids and sediment melts. Combined with published data, the results reveal a systematic compositional transition from the Cretaceous to the Paleogene, characterized by a shift from high (87Sr/86Sr)i and low εNd(t) to low (87Sr/86Sr)i and high εNd(t) values. Trace-element and isotopic modeling demonstrate that this evolution reflects a progressive increase in the proportion of slab-derived fluids in the mantle source, rising from 20–50% to 50–80% of the total subduction component. Spatiotemporally, Cenozoic magmatism exhibits a landward migration trend, consistent with geophysical evidence for a low-angle subduction geometry beneath the SSI. Integrating these lines of evidence, we propose that arc cessation in the north resulted from a progressive decrease in subduction angle that ultimately transitioned to a flat-slab regime at ~20 Ma, highlighting the profound influence of subduction dynamics on mass recycling and arc magmatic evolution.