Christian Brandes

Intraplate seismicity in northern Central Europe is induced by the last glaciation

There is growing evidence that climate-induced melting of large ice sheets has been able to trigger fault reactivation and earthquakes around the migrating ice limit. Even today, the stress due to glacial isostatic adjustment can continue to induce seismicity within the once-glaciated region. Northern Central Europe lies outside the former ice margin and is regarded as a low-seismicity area. However, several historic earthquakes with intensities of up to VII occurred in this region during the past 1200 years. Here we show with numerical simulations that the seismicity can potentially be explained by the decay of the Scandinavian ice sheet after the Weichselian glaciation. Combination of historic earthquake epicenters with fault maps relates historic seismicity to major reverse faults of Late Cretaceous age. Mesozoic normal faults remained inactive in historic times. We suggest that many faults in northern Central Europe are active during postglacial times. This is a novelty that sheds new light on the distribution of postglacial faulting and seismicity. In addition, we present the first consistent model that can explain both the occurrence of deglaciation seismicity and the historic earthquakes in northern Central Europe.

The Mesozoic–Cenozoic tectonic evolution of the New Siberian Islands, NE Russia

On the New Siberian Islands the rocks of the east Russian Arctic shelf are exposed and allow an assessment of the structural evolution of the region. Tectonic fabrics provide evidence of three palaeo-shortening directions (NE–SW, WNW–ESE and NNW–SSE to NNE–SSW) and one set of palaeo-extension directions revealed a NE–SW to NNE–SSW direction. The contractional deformation is most likely the expression of the Cretaceous formation of the South Anyui fold–thrust belt. The NE–SW shortening is the most prominent tectonic phase in the study area. The WNW–ESE and NNW–SSE to NNE–SSW-oriented palaeo-shortening directions are also most likely related to fold belt formation; the latter might also have resulted from a bend in the suture zone. The younger Cenozoic NE–SW to NNE–SSW extensional direction is interpreted as a consequence of rifting in the Laptev Sea.

Structure and kinematics of an outcrop-scale fold-cored triangle zone

Triangle zones are widespread structural elements that link fold and thrust belts with their foreland basins. We present a structural analysis of an outcrop-scale (~6 m [20 ft] wide) triangle zone that is exposed in the siliciclastic Carboniferous strata of the Harz Mountains in northern Germany. The geometry of the triangle zone is critically compared with larger outcrop and seismic-scale structures. The external form of the triangle zone is the same as that proposed for larger examples, with two bounding detachments that dip in opposing directions. However, the interior of the triangle zone is characterized by tight to isoclinal folds. We demonstrate how the triangle zone probably evolved from a fault-bend fold, which accreted further folds behind it. This is an alternative fold-based interpretation for a structure that is commonly modeled as a duplex stack. We present the resulting consequences for seismic interpretation and hydrocarbon reservoir evaluation.

Mesozoic structural evolution of the New Siberian Islands

Abstract The New Siberian Islands are affected by a number of Mesozoic tectonic events. The oldest event (D1a) is characterized by NW-directed thrusting within the South Anyui Suture Zone combined with north–south-trending sinistral strike-slip in the foreland during the Early Cretaceous. This compressional deformation was followed by dextral transpression along north–south-trending faults, which resulted in NE–SW shortening in the Kotelny Fold Zone (D1b). The dextral deformation can be related to a north–south-trending boundary fault zone west of the New Siberian Islands, which probably represented the Laptev Sea segment of the Amerasia Basin Transform Fault in pre-Aptian–Albian times. The presence of a transform fault west of the islands may be an explanation for the long and narrow sliver of continental lithosphere of the Lomonosov Ridge and the sudden termination of the South Anyui Suture Zone against the present Laptev Sea Rift System. The intrusion of magmatic rocks 114 myr ago was followed by NW–SE-trending sinistral strike-slip faults of unknown origin (D2). In the Late Cretaceous–Paleocene, east–west extension (D3) west of the New Siberian Islands initiated the development of the Laptev Sea Rift System, which continues until today and is largely related to the development of the Eurasian Basin.

Towards an Integrative Inversion and Interpretation of Airborne and Terrestrial Data

The aim of the joint research project is to generate information from airborne geophysical measurements that are properly transferred from physically quantitative descriptions of the subsurface (electrical conductivities, densities, susceptibilities) into spatial structures and information matching the understanding of end-users: geologists, hydrogeologists, engineers and others. We suggest new types of inversion, which are integrated in the interactive workflow to support typical trial and error approaches of inverse and forward EM and gravity/magnetic field modelling for 1D and 3D cases. Subsequently, we combine resistivity and density models with geological 3D subsurface models. The integrated workflow minimizes uncertainties in the interpretation of geophysical data and allows a significantly improved and fast interpretation and imaging of the 3D subsurface architecture. The results of the AIDA project demonstrate that combined 3D geological and geophysical models enable a much better reconstruction of the subterraneous space. AIDA stands for “From Airborne Data Inversion to In-Depth Analysis” and is part of the R&D program: Tomography of the Earth’s Crust—From Geophysical Sounding to Real-Time Monitoring.

Integrating High-resolution Shear Wave Seismics and Outcrop Data:A Case Study from Northern Germany

Shear wave seismic surveys allow a detailed assessment of the facies architecture and structural style of the Emme Delta in northern Germany. We combine outcrop and seismic data. The individual architectural elements that form the delta body were defined on the basis of their external geometry and the internal reflector pattern. Outcrops and borehole data were used to relate the seismic facies to the sedimentary facies. Special emphasize was placed on identifying faults, based on the reflector pattern. Faults are imaged as transparent lines that offset the reflectors. Syn-sedimentary faults can be indentified based on the wedge-shape of the growth strata. The faults have planar to slightly listric geometries and show vertical offsets in a range of 2 to 15 m. They form small graben and half-graben systems, which locally show roll-over structures. The fill of the half-grabens has a wedge-shaped geometry, with the greatest sediment thickness close to the fault.