The spatio-temporal variations of soil gas in the seismic fault zone produced by the 12 May 2008 Wenchuan Ms 8.0 earthquake were investigated based on the field measurements of soil gas concentrations after the main shock. Concentrations of He, H2, CO2, CH4, O2, N2, Rn, and Hg in soil gas were measured in the field at eight short profiles across the seismic rupture zone in June and December 2008 and July 2009. Soil-gas concentrations of more than 800 sampling sites were obtained. The data showed that the magnitudes of the He and H2 anomalies of three surveys declined significantly with decreasing strength of the aftershocks with time. The maximum concentrations of He and H2 (40 and 279.4 ppm, respectively) were found in three replicates at the south part of the rupture zone close to the epicenter. The spatio-temporal variations of CO2, Rn, and Hg concentrations differed obviously between the north and south parts of the fault zone. The maximum He and H2 concentrations in Jun 2008 occurred near the parts of the rupture zone where vertical displacements were larger. The anomalies of He, H2, CO2, Rn, and Hg concentrations could be related to the variation in the regional stress field and the aftershock activity.

No abstract

<p>With an increasing number of global and regional plate reconstruction models established in recent years, the motion of the Porcupine Bank, Irish Atlantic continental margin, underlain by orogeny-related pre-rift crustal basement terranes, have been investigated and restored as well.  However, these reconstructed models of the Porcupine Bank margin mainly depend on potential field data analysis and lack seismic constraints, failing to reveal the role of inherited crustal sutures during rifting and associated crustal deformation over geological time. In this study, five deformable models with distinct structural inheritance trends are established in GPlates by adjusting a previously published regional restoration model for the North Atlantic realm. For each model, driving factors (e.g., such as whether the Orphan Knoll is included, the altered rotational poles of the Flemish Cap, and the motion of the eastern border of the Porcupine Basin) are also taken into consideration. Crustal thicknesses from gravity inversion and seismic refraction data modelling are compared against those from these deformable plate reconstruction models to identify the most geologically reasonable one. The resulting preferred model has the Porcupine Bank subdivided into four blocks with each experiencing polyphase rotations and shearing prior to final continental breakup, implying strong inheritance and segmentation of the Porcupine Bank and the Porcupine Basin. The derived reconstructed paleo-positions over time of the Flemish Cap and the Porcupine Bank within the deforming topological network reveal new and evolving conjugate relationships during rifting, which are assessed using regional seismic transects from both margins. Finally, extensional obliquity between both margins is quantitatively restored, showing time-variant orientations due to the rotation and shearing of associated continental blocks, which contributes to unraveling the spatial and temporal evolution of southern North Atlantic rifting during the Mesozoic, prior to the initiation of seafloor spreading.</p>

Published plate reconstructions have provided insights regarding the formation of the North Atlantic, in which the motion of the Porcupine Bank, on the Irish Atlantic margin, underlain by orogenic pre‐rift crustal basement terranes, is investigated and restored. Previous reconstructions of the Porcupine Bank mainly relied on potential field data rather than seismic constraints and failed to reveal the role of inherited crustal terranes during rifting and subsequent crustal deformation. In this study, five deformable plate tectonic models with distinct structural inheritance trends are established in GPlates by adjusting a previously published restoration model for the North Atlantic. For each model, driving factors such as the inclusion of the Orphan Knoll, the Flemish Cap poles of rotation, and the motion of the eastern border of the Porcupine Basin are also considered. To assess the validity of deformable plate models, crustal thickness estimates obtained from gravity inversion and seismic data modeling are compared with those calculated via deformable plate models. The preferred deformable plate model proposes the subdivision of the Porcupine Bank into four blocks with each block experiencing poly‐phased rotation and shearing prior to the final continental breakup, implying strong inheritance and segmentation of the Porcupine Bank and Porcupine Basin. The reconstructed paleo‐positions of the Flemish Cap and Porcupine Bank within deformable regions reveal evolving conjugate relationships during rifting, which are assessed using regional seismic transects from both margins. Finally, extensional obliquity between both margins is quantitatively restored, showing time‐variant orientations due to the rotation and shearing of associated continental blocks.

No abstract