Geza Worum

Slip tendency analysis as a tool to constrain fault reactivation: A numerical approach applied to three‐dimensional fault models in the Roer Valley rift system (southeast Netherlands)

We describe a new numerical approach to constrain the three‐dimensional (3‐D) pattern of fault reactivation. Taking advantage of the knowledge of the tectonic stress field, the ratio of the resolved shear and normal stresses (slip tendency) as well as the direction of the shear stress is calculated at every location on the faults modelled by triangulated surfaces. Although the calculated contact stresses represent only a first order approximation of the real stresses, comparison of the 3‐D pattern of slip tendency with the frictional resistance of the fault can provide useful constraints on the probability of fault reactivation. The method was applied to 3‐D geometrical fault models in the Roer Valley Rift System (southeast Netherlands) which is presently characterized by pronounced tectonic activity. The input stress tensors were constrained by published stress indicators. The analysis demonstrated that the observed fault activity could be explained within a reasonable range of frictional parameters and input stress magnitudes. In addition a fairly good correlation was found between the predicted slip directions and the focal mechanisms of local earthquakes. This suggests that in the study area, fault models being valid in the uppermost part of the crust are suitable to constrain fault reactivation even in the deeper part of the seismogenic layer. The analysis further demonstrated that fault hierarchy and the regional tectonic contexts of the fault system are important factors in fault reactivation. Therefore they always should be taken into account during evaluation of the calculated slip tendency and slip direction patterns.

Tertiary deformation history from seismic section study and fault analysis in a former European Tethyan margin (the Mecsek–Villány area, SW Hungary)

Abstract Outcrop-scale structural data and seismic section interpretation are combined to unveil a very complicated Tertiary deformation history of a once Tethyan margin: the Mecsek–Villany area of Hungary. This combination of data helped to reconstruct the possible activity of individual fault zones. At least four ENE–WSW striking zones—the Northern Imbricates, the South Mecsek zone, the Gorcsony–Mariakemend ridge and the Villany Mountains—were confirmed as regional long-lived transpressive zones with very complicated internal deformation, frequently with oppositely dipping thrust faults. Tertiary structural history began with a roughly N–S-directed shortening in the South Mecsek zone. It was followed by a NE–SW-directed transpression activating practically all important wrench zones together with perpendicular transfer faults. Basins were created along some of these deformation zones, but were also affected by major tilts due to inversion. After a relatively quiescent period in the Middle Miocene, the Late Sarmatian inversion followed. Shortly after, this event was relayed by a NE–SW-directed extension–transtension. An important inversion period characterised by NW–SE compression occurred in Late Pannonian (Messinian), when all the former wrench zones were reactivated as right-lateral shear. This event is responsible for the present topography of the region.

Implications of continuous structural inversion in the West Netherlands Basin for understanding controls on Palaeogene deformation in NW Europe

A detailed analysis of high-quality 3D seismic and borehole data provides new insights into the Palaeogene tectonic history and inversion of the West Netherlands Basin. The inversion characteristics are compared with those of other basins in the region, to provide constraints on the Palaeogene compressional tectonic movements in NW Europe. The inversion of the West Netherlands Basin, which is characterized by the doming of the basin centre and by the reactivation of pre-existing faults in a reverse mode, was found to be the result of a continuous inversion process rather than a distinct tectonic pulse. The intensity of the tectonic movements was not uniform throughout the Eocene and was strongest during the Latest Eocene. These characteristics are similar to those of other basins in the southern North Sea region and in the English Channel area. In addition, a good correlation exists between Alpine tectonic events and the Palaeogene inversion phases. In light of these observations the Latest Eocene inversion pulse in the southern North Sea region can be considered as the culmination of a long-term inversion process that originated from the Alpine collision.

High-resolution quantitative reconstruction of Late Cretaceous-Tertiary erosion in the West Netherlands Basin using multi-formation compaction trends and seismic data: implications for geothermal exploration

A workflow is presented to determine the detailed, high-resolution pattern of erosion in maturely explored Sedimentary Basins by analysing the sonic log-based interval velocity patterns of nine stratigraphic intervals complemented by a geometrical approach involving the extrapolation of 3-D seismic reflectors. The jointly evaluated results of the two approaches not only provide important constraints on the inversion tectonics of a basin, but are also used to better constrain its maturity history and reservoir quality for geothermal energy. The developed workflow is demonstrated for the West Netherlands Basin. The pattern of erosion, which is consistent with observed subcrop maps, shows increasing amount of erosion towards the East and reflects the complex deformation of the basin, in which the reactivation of faults played a major role. Indirectly the results also indicate that continuous, syn-inversion sedimentation was taking place on the flanks of the basin during the Late Cretaceous, while its centre was characterised by non-deposition or slight erosion. For geothermal exploration the inferred variations of amount of erosion has implications for the spatial distribution of porosity which is an important parameter for the assessment of reservoir quality.