Journal of Structural Geology最新文献

The study investigates tectonic movements in northeast Japan by using long-term (2000–2022) global navigation satellite system (GNSS) and tide gauge measurements. The effect of the 2011 Tohoku-Oki earthquake including the other eight seismic events that occurred within this period is also discussed using GNSS time-series. The result showed the break in GNSS-time series because of occurred earthquakes and pointed out tectonic movements significantly. The GNSS sites located in the central and southern parts of northeast Japan showed that the velocity vectors have strong internal variation and suggest the existence source of alternative deformation because of geological terranes within the region. A least square approach was used, and the trend of sea-level measurements was fitted with the straight line. The obtained results from tide gauge measurements showed a rising trend at almost every site and indicated lithospheric uprising movement because of tectonic activities. This is possible because of the ongoing subduction of the Pacific and Philippine Sea plates beneath the Eurasian and North American plates.

The longer time for recording large earthquakes on a plate boundary fault, the better that understanding of large earthquake rupture behavior and seismic hazard on the fault zone. However, large earthquakes (M ≥ 7) are rarely recorded on the boundary fault with slow slipping rate, such as the Red River fault zone (RRFZ), which is an important plate boundary fault that marks the southwestern boundary of the Yangtze platform or south China block. There have been no large earthquake records on the southern segments (including the segment in Vietnam) of the RRFZ since historical earthquake records began in 886 AD, except the 1652 Midu M 7 earthquake and the 1925 Dali M 7 earthquake on the northern segment. The southern segment of the RRFZ will not have a large earthquake in the future or as a large earthquake seismogenic zone with a long period of recurrence, remains controversial, in part because of the absence of constraints from geological evidence. This controversial seriously restricts the risk assessment of future large earthquakes on the southern segment of the RRFZ. By careful interpretations of high resolution remote sensing images, in combination with a detailed field geological and geomorphic survey, we found a series of fault valleys and bedrock outcrops from Gasha toYaojie and Yuangjiang to Hekou on the southern segment of the RRFZ. Multiple trench excavation and radiocarbon dating sample analyses show that the mid valley trace in the southern segment of the RRFZ is an active fault. Geological and geomorphic evidence from Gasha to Yaojie and Yuanjiang to Hekou indicate that the mid valley trace in the southern segment of the RRFZ exhibits dip slip and dextral strike slip motion characteristics. This result is inconsistent with those of previous studies that the mid valley trace is purely strike slip. Furthermore, trenches opened on the range front trace in the southern segment of the RRFZ in Ejia are found to still be active, differing from previous studies. Thus, the seismic hazard on the southern segment of the RRFZ should be reevaluated.

We study in detail the M_w 5.4 September 6, 2021 Tofalaria earthquake occurred in a mountain area of the Eastern Sayan which is characterized by a low level of seismic activity. An interest in the seismic event is caused, on the one hand, by poor knowledge about stress-strain field of the crust in the considered region, and, on the other hand, by its relation to the NW segment of the ancient Main Sayan fault – a structural boundary between the Sayan-Baikal fold belt and the tectonically stable Siberian platform. Seismic moment tensors and hypocentral depths of the mainshock and its largest aftershock (M_w 4.6) are inverted from intermediate-period surface wave amplitude spectra calculated at the stations located at teleseismic distances. Integral source parameters of the mainshock, characterizing its spatio-temporal development, are also estimated and the fault plane is determined. Epicenters of 31 aftershocks with M ≥ 1.8, occurred up to the end of 2021, are constrained from body waves recorded at regional seismic stations. The obtained results show that the Tofalaria earthquake occurred under the influence of the SW-NE compression, which is observed in Western Mongolia. Focal mechanism of the largest aftershock and the NE elongation of the aftershock epicentral field (22 km) indicate stress redistribution after the mainshock in a local crustal volume, bordered by small-scale faults.

Folds are common structures that provide valuable insights into the direction and amount of shortening and the rheological properties of deformed rocks. Most thin plate folding theory started from M.A. Biot has historically been applied to isotropic materials, but rocks are often anisotropic due to the presence of tectonic foliations, bedding, veins, dykes, etc. Mechanical anisotropy can enhance partitioning of deformation, resulting in low-strain domains and localised high-strain shear domains. Using the Viscoplastic full-field code coupled with the modelling platform Elle (VPFFT-Elle), we investigate the evolving fold geometries, stress field and strain-rate field differences and redistributions resulting from layer-parallel shortening deformation of an isotropic, competent layer embedded in an anisotropic, weaker power-law viscous matrix. We focus on the effect of the orientation of the mechanical anisotropy relative to the competent layer. The simulation results illustrate that the deformation localisation behaviour, and hence fold geometry, depend on (i) the initial orientation of the anisotropy, (ii) the intensity of anisotropy, and (iii) strength of the competent layer, relative to that of the matrix. Variation in the localisation behaviour resulting from different strain-rate distributions lead to two end-member fold geometries: (1) classical Biot-type buckle folding and thickening of the competent layer coupled to the formation of a new axial-planar crenulation cleavage in the matrix, and (2) what we call ‘shear-band folding’ in which sections of the competent layer are offset due to the formation of shear bands in the matrix with opposite sense of shear. This leads to rapid fold amplification. Classical Biot-type buckle folds dominate when the initial anisotropy is parallel or subparallel to the shortening direction, while shear-band folds dominate when the initial anisotropy is normal or at high angle to the shortening direction. Results presented here contribute to our understanding on how mechanical anisotropy controls folding and the rearrangement of the matrix components. Furthermore, the modelled scenarios can serve as a “virtual glossary” to compare real folds in different tectonic settings, providing insights into the possible pre-fold configuration of the folded layer and its anisotropic matrix.

Balanced cross sections through thrustbelts affected by post-orogenic extension reveal that normal faults are mostly developed in the backlimbs of pre-existing, asymmetric, fault-propagation and detachment folds. Outcrop study, geological cross section balancing, reflection seismic interpretation and numerical modeling in the Eastern Balkans indicate that the nucleation of these normal faults is affected by the occurrence of plastic strain zones in backlimbs, represented by clusters of small-scale dilatant shear fractures. Thrustbelt segments where these zones did not evolve into thrust faults and became passively rotated into steeper geometries are prone to normal fault development during post-orogenic extension. Instead of developing its own precursor fracture clusters, each normal fault of this type nucleates using pre-existing clusters as a shortcut in its development. Rare occurrences of post-orogenic extension-driven faults, which reactivate entire pre-existing thrust fault ramps or develop in fold forelimbs indicate the existence of other parameters that co-control the development of normal faults in this setting. These parameters include thrustbelt topography as well as variations in décollement geometry and frictional properties.

Characterizing the active deformation of the foreland is particularly valuable for understanding the dynamics of regional structural evolution within active contractional orogens. We focus on the Guman fold, one of the most prominent fold-and-thrust belts along the foothill of the Western Kunlun Mountains (Xinjiang, China). The anticline growing above the blind thrust faults progressively deforms river terraces. However, contemporaneous terrace surfaces are buried under young deposits north of the fold. We propose a novel method that extends terrace surfaces above the forelimb of the fold within the extent of deformation determined on the seismic reflection profile, to estimate the sediment thickness after abandonment of the terraces. Furthermore, cosmogenic nuclide (¹⁰Be and ²¹Ne) depth profile dating was used to determine the exposure ages of the two terrace surfaces: 413–673 kyr for T1b and 3.7–5.2 Myr for T3b. Combining the age and deformation amount, the slip rate on the frontal fault ramp within the fold is estimated to be 0.4^+0.2/_-0.1 mm/yr and 0.17^+0.07/_-0.03 mm/yr since the abandonment of the T1b and the T3b terrace respectively. These rates represent the recent crustal shortening rate across the Guman fold and likely account for most of the total crustal shortening rate across the Western Kunlun Mountains. However, these rates appear to be notably lower by an order of magnitude compared to the long-term (∼23 Ma) average crustal shortening rate (∼1.1–2.6 mm/yr) in this region. This may indicate a rapid slowing down of the deformation at the scale of the whole Western Kunlun Mountains, possibly related to a regional reorganization.

Rivers tend to alter the morphology of their bed and valley as a response to changes in their base level. The study of a drainage basin's tectonic activeness is very important. But especially in areas where rates of vertical tectonic movements are scarce, the morphometric analysis can be proved to be a very accurate method for assessing the effects of neotectonic movements on a drainage network. This method is easy to apply, as it does not require a lot of data. This study concerns the drainage basin of Acheron river in Epirus, Greece. In order to assess of river's response to active tectonic movements, a morphometric analysis was conducted, using a digital elevation model (DEM). Seven morphometric parametres and five geomorphic indices were calculated for the entire basin, as well as 9 sub-basins. Subsequently, each sub-basin was categorised into three categories regarding tectonic activeness (high-medium-low) for each index individually. The relative active tectonics index was also calculated, as the average of the aforementioned morphometric parametres and geomorphic indices. Based on that, each sub-basin was categorised into three categories regarding the overall tectonic activeness (low-medium-high). These results were compared with the drainage pattern and field observations, so as to gain insights on the tectonic activeness of the sub-basins and the entire basin of Acheron.

Reconstructing the stratigraphic paleosurfaces of a fold is essential for deciphering the folding mechanism, simulating landscape evolution processes, and investigating mineral resource distribution. However, standard methods for reconstructing paleosurfaces in tectonic landforms, primarily applied on large-scale sedimentary basins and orogenic belts, heavily rely on extensive geological data and generally yield low-accuracy results. This limits their applicability to small to intermediate-scale geological structural areas. Therefore, this paper introduces a stratigraphic paleosurface reconstruction method tailored for small and intermediate-scale folds, leveraging structural element features to constrain this reconstruction, which is notably helpful when dealing with sparse geological and topographic data. This method involves several steps. Firstly, define the fold units for diverse landforms. Secondly, extract fold structural elements (FSEs) with diverse geological data. Next, fit the paleo-boundary of each stratum within the two-dimensional (2D) cross-section using elemental feature constraints. Finally, the Morphing technique is applied to interpolate multiple paleo-boundaries, which are then utilized in reconstructing the stratigraphic paleosurfaces through the Contour Reconstruction Algorithm (CRA). To validate the method, tests were conducted on three representative folds in China: the eastern Sichuan comb-like fold belt, the Dayueshan Anticline on Mount Lu, and the Wulongshan Dome near the Huangling Dome. Experimental results demonstrate that utilizing structural features as constraints enables automatic, accurate, and reliable stratigraphic paleosurface reconstruction. The reconstructed paleosurfaces facilitate the analysis of geometric characteristics and structural development mechanisms of folds within the study area. Furthermore, they can be readily incorporated into landscape evolution models (i.e., TTLEM) to simulate realistic topographic evolution and tectonic paleogeographic mapping or construct three-dimensional (3D) solid models.