Journal of Structural Geology最新文献

The ideal development of layer-bound, polygonal faults occurs in an isotropic stress field. However, some populations of layer-bound faults appear to have originated as ‘polygonal’ faults, but display atypical plan-view fault geometries that suggest development under anisotropic stress conditions. High-resolution 2D/3D seismic data in the southern Qiongdongnan Basin displays three tiers of layer-bound faults with distinct strike variations and complex structural patterns that depart from the geometries of isotropic polygonal fault cells. The lower fault tier displays preferred orientations along E-W, NE-SW, NW-SE directions; the middle fault tier shows a primary E-W orientation and a secondary N-S trend; the shallow tier features strong N-S and E-W orientations. Fault patterns in map view include orthogonal, quasi-polygonal and circumferential geometries, among which the orthogonal pattern is dominant in the shallow fault tier. Several factors are inferred to cause these variable geometrical and structural patterns in layer-bound faults, they are: pre-existing tectonic faults, an uplifted region, local slopes, contourite depressions, and large contourite-related channels. The orthogonal fault patterns have longer E-W orientation parallel to the contourite channels and shorter N-S trends perpendicular to the thalwegs. The presence of submarine channels is suggested to locally deflect the stress orientation, which in turn impacts fault patterns.

Fracture stratigraphy study for a subsurface sedimentary rock sequence can be a challenging and demanding task. Typically, the data obtained from seismic and well-logs are heavily impacted by resolution issues and are difficult to interconnect. In this work, we document and extract fracture properties (orientation, density, intensity, etc.) from a layered carbonate sequence for fracture stratigraphy characterization. High-resolution subsurface Ground Penetrating Radar (GPR) data images, coupled with drone and previously documented well-log profiles, were analyzed to achieve the structural characterization task. The studied outcrop is localized in the Potiguar Basin (Brazil), where the Cretaceous Jandaíra Formation carbonates are exposed for hundreds of meters. The sequence is subdivided into an upper packstone/grainstone portion and a lower wackestone bed package. We documented the higher fracture intensity/density in the lower bed package portion, highlighting that depositional texture and intra-bed stylolites control the higher fracture distribution in the sequence. Finally, a 3D conceptual model describing the overall results is presented. This model summarizes and shows the innovative fracture stratigraphy method based on the GPR data analysis.

The South China Sea (SCS) opened due to the extension of a compressional setting of the paleo-Pacific subduction. The pre-existing structure significantly influences the geometry of rift basins and the kinematic evolution of the rifting. However, structural evidence of the paleo-Pacific subduction in the northeastern SCS remains enigmatic. The deformation front, serving as the structural evidence of paleo-subduction, is associated with accretionary style deformation and would be reactivated during the subsequent extension phase. In this study, we use a multi-channel seismic profile to investigate the pre-existing structure related to the paleo-Pacific subduction in the northeastern SCS, emphasizing the influence of pre-existing structure on the rift evolution. The seismic profile reveals imbricate reflections in the lower crust. These reflections are interpreted as the deformation front of the Paleo-Pacific subduction. Notably, the deformation front is hyperextended in the Chaoshan Depression. The result of the stretching factors indicates that the ductile lower crust experienced preferential thinning during the rifting beneath the Chaoshan Depression. In the northern part of the profile, a transparent reflection zone was identified and interpreted as a magmatic arc related to Mesozoic subduction. One major achievement of our study is these seismic reflections provide the structural evidence for Paleo-Pacific subduction and reveal that the northeastern SCS has experienced crustal shortening and imbrication through a series of dipping thrusts. Subsequently, we discuss the role of pre-existing structures in lower crustal thinning and continental rifting. We propose the deformation front of the Mesozoic subduction, as a pre-existing weakness, facilitated the kinematic evolution of the rifting in the northeastern SCS during the Cenozoic.

Intraplate strike slip deformation structures play a crucial role in understanding how the earthquake are triggered, and respond to long-term deformation in plate interiors. One of the examples for intraplate structure is the Lake Salt Fault Zone (LSFZ) in Türkiye, located at the Central Anatolia region which has hosted a few moderate magnitude earthquakes. The LSFZ extends in NW-SE direction along the eastern border of the Lake Salt basin. In the western and central sections, it exhibits a rather linear trace, and it marks the west-northwestern boundary of the Cappadocian plateau. Along its strike, two big cities, namely, Aksaray and Niğde, and some significant eruption centers (the Hasan, Keçibuyduran and Melendiz Mountain stratovolcanoes) are located, and there is a 12 km right lateral offset. LSFZ has four main segments, namely, Karacaören, Keçikalesi, Obruk and Büyükkaraoğlan fault segments, and they have hosted two moderate-sized (Mw = 5.1 to 5.2) earthquakes (on September 20, 2020 and February 25, 2023) at the localities approximately 5 km ENE and SSW of Obruk Town (Niğde). Their focal mechanisms revealed that the LSFZ exhibits dominantly dextral strike-slip faulting with normal component. The vertical and horizontal displacement rates along the LSFZ are 0.14 mm/yr and 4.6 mm/yr, respectively. The recurrence interval of earthquakes of Mw ≥ 6.7 on the LSFZ is more than one thousand years, owing to the low slip rate. We propose that the LSFZ is in a seismic gap having potential to host a large earthquake.