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Multi-component seismics in over-deepened Alpine basins

This project is being carried out at two locations in Germany and Austria. It integrates high-resolution three-dimensional (3-D) and multi-component seismic for the improved structural and facies characterisation of overdeepened valleys and basins and, hence, processes within these structures. The investigation is affiliated to the ICDP project: "Drilling Overdeepened Alpine Valleys (DOVE)".

Motivation

The European Alps are surrounded and pervaded by valleys and basins that were primarily eroded and refilled during the Pleistocene ice ages. Some of these structures reveal an overdeepened character, i.e. the glaciers eroded deeper than the base of the fluvial sequence during the glaciations. It is assumed that this erosion was caused by high-pressure meltwater beneath the ice. After the erosion, the overdeepened valleys and basins were either completely or partially filled with glacial or meltwater deposits. Lake Constance is the most prominent example of an overdeepened basin in Germany. These structures are of scientific and societal relevance for a variety of reasons, e.g. in the context of groundwater, tunnelling, and the safety of nuclear repositories (Preusser et al. 2010).

Fig. 1: Alpine area with zones of over-deepened valleys and basins (red), the catchment areas of the main glaciers (blue), as well as the borehole locations (numbered) planned for the DOVE part of the ICDP project (Anselmetti et al. 2016; unpubl.). This figure also shows the maximum extent of the Pleistocene glaciation (black line) as well as the last glacial maximum (pink line).
Fig. 2: Schematic diagram of erosion of an overdeepened basin. (a) fluvial erosion, (b) subglacial erosion and (c) refilled over-deepened basin, to be investigated by DOVE (after Anselmetti et al. 2016; unpubl.).

The DOVE ICDP project (Drilling Overdeepened Alpine Valleys; Anselmetti et al. 2016) will drill into sediments of a number of overdeepened basins to gain insights into the spatial and temporal extent of the various glaciations and, therefore, the climatic history. Other questions concern the genesis and filling of the basins.

'Multi-component seismic' project

This DFG-funded project investigates the possible use and benefits of reflection seismic with multi-component technology, prior to the actual drilling of the scientific wells. For this reason, seismic surveys were carried in recent years at two locations: the Tannwald Basin, located 50 km to the north of the Alps, and the inner-Alpine Lienz Basin. In addition to high-resolution P-wave seismic for structural and facies characterisation, the surveys also included S-wave registration with 1- and 6-components (horizontal source stimulation in two directions and 3-component receivers).

Objectives

  • To establish a structural 3-D model with reflection seismic to determine basin depth, possible faults, and the main reflectors,
  • To characterise multi-phase glacial deposits/erosion, facies, and mass movements,
  • To investigate anisotropy by application of P- and S- waves.

First results

Fig. 3: Geological map of the Tannwald Basin with location of existing wells, as well as the seismic lines measured with P-waves (vertical source and receivers; black lines), SH-waves (horizontal source and 1-component receivers, both orthogonal to the line direction; red lines), and multi-component (horizontal sources in two directions and 3-component receivers; yellow line).

Tannwald Basin

The P-wave results reveal the structure of the basin that cuts into Tertiary Molasse sediments. Various facies can be differentiated in the basin fill and provide information on how the basin was filled. For instance, we have identified one block of Molasse within the basin fill that must have been transported there after basin erosion. Although the evaluation of the SH-waves and multi-component lines is still ongoing, they already indicate findings complementary to the P-wave seismic.


The results were used to establish a basin fill model and to select a drilling site for the DOVE research borehole.

Fig. 4: P-wave section of lines 2 (left) and 3 (right), including interpretation, and the Schneidermartin borehole. The letters refer to the interpreted seismic facies.
Fig. 5: Satellite image of the Lienz Basin with the location of the seismic lines measured with P-waves (vertical source and receiver; blue lines), SH-waves (horizontal source and 1-component receivers, both orthogonal to the line direction; red lines) and multi-component (horizontal sources in two directions and 3-component receivers; yellow line).

Lienz Basin

The data from the Lienz Basin is currently being evaluated. Initial findings from the P-wave surveys reveal a deeply cut valley of approx. 600 m depth. In addition, internal structures can also be identified that are crucial for the selection of a suitable drilling location.

Project-relevant literature:

  • Improving the processing of vibroseis data for very shallow high-resolution measurements. - Near Surface Geophysics, 5(3), 173-182.
    2007, BUNESS, H.
  • Finite difference modelling to Evaluate Seismic P-Wave and Shear Wave Field Data.  Solid Earth, 6, 33-47; doi: 10.5194/se-6-33-2015.
    2015, BURSCHIL, T., BEILECKE, T. & KRAWCZYK, C.M.
  • The Quaternary of the southwest German Alpine Foreland (Bodensee-Oberschwaben, Baden-Württemberg, Southwest Germany). E & G Quaternary Science Journal, 60 (2-3), 306-328; doi: 10.3285/eg.60.2-3.07.
    2011, ELLWANGER, D., WIELANDT-SCHUSTER, U., FRANZ, M. & SIMON, Th. 
  • The Heidelberg Basin, Upper Rhine Graben (Germany): a unique archive of Quaternary sediments in Central Europe. Quaternary International, 292, 43-58.
    2013, GABRIEL, G., ELLWANGER, D., HOSELMANN, C., WEIDENFELLER, M., WIELANDT-SCHUSTER, U. & The Heidelberg Basin Project Team
  • Surveying near-surface depocentres by means of shear wave seismics. First Break, 31 (8), 63-75.
    2013, POLOM, U., BAGGE, M., WADAS, S., WINSEMANN, J., BRANDES, C., BINOT, F. & KRAWCZYK, C.M.

Project Scientist

Dr. Thomas Burschil

 

Funding

DFG

Duration

2015-2019