Active out-of-sequence thrusting in the Molasse Basin constrained by a multidisciplinary approach (Eastern Alps, Austria)

Recent measurements of Qβ−1 of S waves in the lithosphere for frequency range from 0.02 to 25 Hz show a remarkable frequency dependence and systematic variation from place to place depending on the current tectonic activity. In order to test the hypothesis that the attenuation of S waves may be caused by the loss of energy by scattering due to heterogeneity, the amplitudes of S and coda waves were measured simultaneously for 900 local earthquakes in the central Japan for various frequency bands. The data were interpreted using the S to S single‐scattering theory for coda waves, which is now supported by the observed agreement between Q of coda and Qβ, and also by the observed identical local site effect on coda and S waves. The result shows that the loss of energy from S waves required to explain coda amplitudes agrees with the attenuation of S waves within the uncertainty of measurements. This conclusion is supported by several recent studies on Q of coda, Q of Lg, Qβ, and coda excitation by other workers.

The in-situ hydraulic fracturing stress measurements have been carried out around the coastal marginal land in Fujian Province. And the characteristics of magnitude, direction and distribution of tectonic stress have been obtained. Based on the observed stress data, the characteristics and activities of fault zones are analyzed and studied in the paper according to the Coulomb friction criteria. (1) The maximum horizontal principal compressive stress is in the NW-WNW direction from the north to the south along the coastline verge, which is parallel to the strike of the NW-trending fault zone, consistent with the direction of principal compressive stress obtained from geological structure and across-fault deformation data, and different from that reflected by focal mechanism solution by about 20°. (2) The horizontal principal stress increases with depth, the relation among three stresses is S H>S v>S h or S H≈S v>S h, and the stress state is liable to normal fault and strike-slip fault activities. (3) According to Coulomb friction criteria and taking the friction strength μ as 0.6–1.0 for analysis, the stress state reaching or exceeding the threshold for normal-fault frictional sliding near the fault implies that the current tectonic activity in the measuring area is mainly normal faulting. (4) The force source of current tectonic stress field comes mainly from the westward and northwestward horizontal extrusions from the Pacific and Philippine Plates respectively to the Eurasian Plate.

We present 81 paleomagnetic sites (Early Triassic to Early Cretaceous) from the central sector of the northern Calcareous Alps (NCA, Eastern Alps, Austria and Germany). Stepwise thermal demagnetization defines three magnetic directions mostly carried by low unblocking temperature and low‐coercivity minerals: J3, 350°; J2, 500°; J1, 575° and 680°. J3 and J2 show positive inclinations, whereas J1 (very seldom) is of dual polarity. The fold tests show that a J3 can be interpreted as a postfolding and posttilting remagnetization and J2 as a postfolding and pre(syn)tilting. J1 can be considered as primary because of the occurrence of two polarities and evidence presented by other authors in the area. All three components show a systematic and significant clockwise rotation after comparing with the expected European references. J2 or J1 are marked by higher rotation values than J3. J2 shows different inclinations depending on the structural position (north or southward dips). Considering the structural evolution and the observed inclinations, the first postfolding and pretilting remagnetization event (J2) could have taken place between Late Cretaceous and Eocene times but certainly before the thrusting of the NCA over the Rhenodanubian Flysch and northward tilting caused by the stacking of the lower Austroalpine nappes. The second postfolding and posttilting remagnetization (J3) would have been acquired after the final thrusting of the NCA over Penninic units. From then, the NCA behaved as a set of rigid blocks recording the main stage of vertical axis clockwise rotation (65° in average) associated with the continental collision. The variable degree of rotation in the different positions (from 40° to 134°) can be explained by individual vertical axis rotation in a block system trying to adjust to space problems. The constant declination differences between J2 and J3 (25° in average) would reflect the rotation related with the lateral differences of shortening during the oblique thrust of the Austroalpine units over the Penninic units.

The Oligocene-Miocene Molasse basin along the northern rim of the Swiss Alps is affected by a major fault zone that separates Plateau Molasse to the north from Subalpine Molasse to the south. As a result of alpine compression, thrusts along this zone brought up Subalpine Molasse rocks by an amount of up to 1000 m. On the northern shore of Lake Geneva, near the City of Lausanne, the fault zone is well defined (Fig. 1). However, its extension in the lake and on its southern shore is not well known. Geology on both sides of the lake, however, indicates that major changes in the distribution of Molasse units occur in this region. Locating the Molasse fault zone across Lake Geneva would help to better understand geology and would provide important constraints on tectonic models of the Alps. In order to study the extension of the Molasse fault zone across Lake Geneva, we conducted a 2-D high-resolution multi-channel seismic reflection survey. Molasse units in the lake are overlain by Quaternary sediments up to 300-400 m thick (Vernet et al. 1974). Our data imaged these sediments and detected several faults in the Molasse units.

Structure of the lithosphere beneath the Eastern Alps (southern sector of the TRANSALP transect)

Holocene reactivation of the aseismic Meers fault in southwestern Oklahoma illustrates the limitation of using the historical seismic record for identifying hazardous faults in the central United States. The 26- to 37-km-long fault scarp is one of the few known scamps recording Holocene movement in the central and eastern United States. Two documented late Holocene slip events, each with about 2.5 m of net slip and estimated M s ranging from 6¾ to 7¼, identify the Meers fault as a potentially hazardous fault. During Carboniferous and Early Permian tectonism, the Meers fault displaced rocks of sharply contrasting magnetic properties. Analysis of aeromagnetic data and twelve ground-magnetic profiles provides a detailed look at the fault within the magnetic basement. Because subsequent reactivation has been minor and of an opposite sense, the pronounced magnetic anomaly associated with the Meers fault reflects Paleozoic structures in the magnetic basement. The location of the Holocene fault scarp corresponds to the strong horizontal magnetic gradient caused by Paleozoic offset of magnetic basement, indicating that the Paleozoic fault controlled Holocene displacement. Two features apparent in both sets of magnetic data are splays of the Meers fault northwest of the Holocene scarp and dikelike bodies immediately south of the fault. Magnetic susceptibility measurements and rock magnetic data from unoriented core penetrating a dikelike body were incorporated into models of the ground-magnetic profiles. In most cases, secondary faults mapped or visible on low-sun-angle photographs correspond to faults modeled from magnetic data. This correlation shows that preexisting structures probably controlled secondary faulting. However, secondary faults at the southeastern end of the 26-km long continuous fault scarp, previously interpreted from low-sun-angle photography, are not apparent in the magnetic data. Of importance to seismic hazard evaluation, the magnetic models show that the northwestern splays probably begin at the northwestern end of the reactivated segment and may indicate a persistent rupture propagation barrier to the west. In addition, the models show the dip of the Meers fault to be nearly vertical to about 0.5 km depth. This dip is consistent with the nearly straight fault trace, results of trenching studies, interpretation of shallow seismicreflection data, and regional gravity and aeromagnetic models. In the present-day strike-slip regional stress field, the observed up-to-the-north Holocene displacement suggests that either the fault continues to dip steeply at depth or the regional stress field is approaching a normal-faulting stress regime. If the former is true, the scarcity of near-vertical faults with similar orientation within the area of the southern Oklahoma aulacogen implies that few are likely candidates for reactivation.

Confined channel-levee complex development in an elongate depo-center: Deep-water Tertiary strata of the Austrian Molasse basin

The undisturbed stress state of the subsurface is a key parameter for the assessment of geological barrier integrity in deep geological repositories. A robust knowledge of the stress state is required for forward simulations that predict the evolution of the deep geological repository during building, canister emplacement, and post-closure phase. However, stress magnitude data will always be sparse and point-wise and thus not sufficient to allow a continuous characterization of the stress field. 3D geomechanical-numerical models are incorporated to mitigate this shortcoming. The significance of such a model is tied to the stress magnitude data records whose availability is generally low and subject to measurement errors. In turn, the uncertainties of the modelled 3D stress state are large which lowers the predictive values of the ensuing forward models. Here, we present a novel approach to reduce the uncertainties of a modelled stress state (Ziegler and Heidbach, 2023).In a first step we estimate all possible and realistic stress states with respect to the available stress magnitude data and their uncertainties. This provides an overall quantification of the range of stress states that are supported by data. In a second step we limit this usually very large range of stress states using additional indirect stress information to determine upper and lower limits. Formation integrity tests (FITs) are used as a lower limit for the stress state. Observed borehole wall failures (drilling induced tensile fractures and borehole breakouts) provide an estimate of the quality of a modelled stress state in relation with estimations of the rock strength. Observed seismicity and observed seismological quiescence in connection with a failure criterion is used as an upper constraint of the stress state. These additional data allow to identify the probability of a modelled stress state based on its agreement with observations. A weight is estimated for each modelled stress state in a formalized Bayesian approach. This allows an improvement in the significant interpretation of the initial stress state in terms of its robustness and transparency.Results from an explanatory model and a case study in the Bavarian Molasse Basin show an improved significance in terms of clearly reduced model uncertainties. The amount of uncertainty reduction, however, depends significantly on the quality, suitability and assessment of the additional information. Reference:Ziegler, M. O., & Heidbach, O. (2023). Bayesian quantification and reduction of uncertainties in 3D geomechanical-numerical models. Journal of Geophysical Research: Solid Earth, 128, e2022JB024855. https://doi.org/10.1029/2022JB024855

Petrological data provide a good record of the thermal structure of deeply eroded orogens, and, in principle, might be used to relate the metamorphic structure of an orogen to its deformational history. In this paper, we present two‐dimensional thermal modelling of various subduction models taking into account varying wedge geometry as well as variation of density and topography with metamorphic reactions.The models clearly show that rock type accreted in the wedge has important effects on the thermal regime of orogenic wedges. The thermal regime is dominated by radiogenic heat production. Material having high radioactive heat production, like the granodioritic upper crust, produces high temperature metamorphism (amphibolitic conditions). Material with low radioactive heat production results in low temperature metamorphism of greenschist or blueschist types depending on the thickness of the wedge.Application of this model to seemingly unrelated areas of the Central Alps (Lepontine Dome, Grisons) and Eastern Alps (Tauern Window) explains the coexistence and succession of distinct Barrovian and blueschist facies metamorphic conditions as the result of a single, continuous tectonic process in which the main difference is the composition of the incoming material in the orogenic wedge. Accretion of the European upper continental crust in the Lepontine and Tauern Domes produces Barrovian type metamorphism while accretion of oceanic sediments results in blueschist facies metamorphism in the Valaisan domain.

Recent studies established the lithological and chemical sediment evolution in the Lower Austrian Molasse Basin (LAMB), a part of the North Alpine foreland basin, during the Early Miocene. In this study, we aim to integrate the clay mineralogy of seven wells across the LAMB with a newly proposed lithostratigraphy, and to infer implications for provenance, palaeo-geography and palaeoclimate. The results of our qualitative and quantitative evaluation of the clay-sized fraction with x-ray diffractometry largely support the stratigraphic model. The early stage of foreland basin formation (Egerian/Eggenburgian?) is represented by kaolinite contents up to 93 % in the clay sized fraction. This indicates an orogen-external source, i.e. the Bohemian Massif, and erosion of intensively chemical weathered products during this early Molasse basin stage. The over-lying marine Robulus Schlier (lower/middle Ottnangian) is characterized by a distinctly reduced kaolinite content and overall increased illite content compared to the other formations. Illite was predominantly provided from denudation of the rising Eastern Alps, i.e. characterizing the orogen-internal provenance. The pelites of the overlying carbonate poor Traisen Formation (upper Ottnangian) show again a higher kaolinite and smectite content. In the largely coeval basinal Wildendürnbach Formation, smectite reaches up to 70 % in the clay sized fraction. Peak smectite values may be linked to volcanic ash input from the nearby Carpathian volcanic arc. Generally rising smectite versus illite ratios during the Ottnangian-Karpatian could point to a warming and intensified chemical weathering of the rising Alpine orogen.

4D seismic monitoring appears to be quite an expensive and pinpoint tool to increase the efficiency of oil and gas fields' exploitation. To reach the desired profit results, it is necessary to select candidate-fields very accurately and provide individual monitoring parameters on every stage. In this work, the opportunity of a 4D marine seismic survey on the Filanovsky field, which is prepared for development, is being examined. The questions of technique's efficiency in these particular geological and geographical conditions are discussed. To conduct a feasibility study, 4D seismic modelling of possible reservoir development effects was performed and the most suitable design of marine 4D seismic survey was proposed considering international experience of such projects. A full package of interdisciplinary information was utilized as initial data: 3D seismic interpretation results, AVA seismic inversion results, well log data interpretation, core data laboratory testing results, results of reservoir simulation and geomechanical modeling. 4D modeling was performed by calculating 3D elastic parameter models for various periods of field development according to flow simulation and geomechanical modeling results. Then these petro-elastic models were used to generate synthetic seismic volumes. The possibility of 4D seismic effects appearance was proved based on the modeling outcome. After analyzing the latest field survey techniques of 4D seismic monitoring, the most effective scenario of their realization on the Filanovsky field was suggested taking into account all the specific aspects of geology and the local area. The 4D marine survey was completely designed according to all efficient parameters calculation.

The topography of the eastern Southern Alps (ESA) reflects indenter tectonics causing crustal shortening, surface uplift, and erosional response. Fluvial drainages were perturbed by Pleistocene glaciations that locally excavated alpine valleys. The Late Miocene desiccation of the Mediterranean Sea and the uplift of the northern Molasse Basin led to significant base level changes in the far field of the ESA and the Eastern Alps (EA), respectively. Among this multitude of mechanisms, the processes that dominate the current topographic evolution of the ESA and the ESA‐EA drainage divide have not been identified. We demonstrate the expected topographic effects of each mechanism in a one‐dimensional model and compare them with observed channel metrics. We find that the normalized steepness index increases with uplift rate and declines from the indenter tip in the northwest to the foreland basin in the southeast. The number and amplitude of knickpoints and the distortion in longitudinal channel profiles similarly decrease toward the east. Changes in slope of χ‐transformed channel profiles coincide spatially with the Valsugana‐Fella fault linking crustal stacking and uplift induced by indenter tectonics with topographic evolution. Gradients in χ across the ESA‐EA drainage divide imply an ongoing, north directed shift of the Danube‐ESA watershed that is most likely driven by a base level rise in the northern Molasse basin. We conclude that the regional uplift pattern controls the geometry of ESA‐EA channels, while base level changes in the far field control the overall architecture of the orogen by drainage divide migration.

Control of mechanical stratigraphy on the stratified style of strike-slip faults in the central Tarim Craton, NW China

Due to heavy industrialization and ongoing fossil fuel burning, CO2 emissions have been a major contributor to climate change and enhanced greenhouse gases. The growing public concern motivates considerable study towards discovering an efficient technique of managing and lowering the emission amounts, and CO2 collection and subterranean storage have been presented as viable alternative. In order to assess the geomechanical behavior of the multilayered In Salah CO2 storage site, a two-dimensional finite element model of fault activation processes in the context of CO2 storage was conducted. It is 4 km wide and 2 km deep and includes the key domains and formations (overburden, main caprock, lower caprock, and underburden). The simulation results suggest that the influence of fault reactivation under base pressure of 32 MPa causes peak vertical deformation of 0.044 m in the caprock and 0.015 - 0.020 m displacement at the surface layers. The obtained modelling results are in agreement with InSAR monitoring results conducted at the site. The geomechanical model was moderately sensitive to a decrease in the effective stress ratio and fault dip angle. The scenario with k = 0.5 performed a considerable displacement reduction compared to the benchmark run. The simulation with a 30° fault angle demonstrated a more pessimistic outcome with a larger displacement field, which could heighten the risks associated with the low-angle faults in the areas of high horizontal stress distribution.

This paper dialogues with the traditional historiographical reading of the Laurentian Complex, seeking to complement the established studies on the abstract modular Order by focusing on its material implementation. The essay advances the thesis that the Laurentian site – defined by pre-existing structures and a complex "piecemeal" evolution – is a "palimpsest" whose current form is the result of a continuous process of material adaptation.The Renaissance "module" is framed not as a rigid grid, but as an ideal norm (regula) constantly mediated by constructional practice (facture) and the inevitable in situ adaptations. This essay presents a "knowledge project" based on an integrated digital survey (TLS, GNSS, UAV). This apparatus is not aimed at a purely abstract verification of the module, but rather at scientifically measuring the discrepancy between the ideal norm and the reality of the construction site. The unified metric infrastructure allows, for the first time, for the mapping of three-dimensional discontinuities. This approach quantifies the structural and altimetric differences between the foundations, the transept of the first phase, and the subsequently built nave, as well as the physical constraints of pre-existing elements. This process transforms the Survey from a documentary act into a hermeneutic investigation. The Drawing (Representation) thus becomes the critical synthesis that "puts in order" the palimpsest, making legible the complex stratification of adaptation, which constitutes the material realisation of the Order on the site.