EGU2015 - 10412 HS8.1.2

Contact:Dipl.-Geophys. Tatiana Feskova | tatjana-lew@hotmail.detatiana.feskova@ufz.de | +49341/235-1827 | www.ufz.deHelmholtz-Centre for Environmental Research - UFZDepartment Monitoring and Exploration Technologies (MET)Permoserstrasse 15, 04318 Leipzig, Germany

Hillslope characterization in terms of geophysical units based on the joint interpretation of

electrical resistivity and seismic velocity data1,2 1, 2Tatiana Feskova , Peter Dietrich

1. Helmholtz-Centre for Environmental Research – UFZ, Department Monitoring and Exploration Technologies, Leipzig, Germany 2. Eberhard Karls University of Tübingen, Department of Geosciences, Tübingen, Germany

Acknowledgement:The scientific research is conducted in the framework of CAOS (Catchment As Organized Systems) project and supported by the National Research Fund of Luxembourg and the Deutsche Forschungsgemeinschaft. This work was kindly supported by Helmholtz Impulse and Networking Fund through Helmholtz Interdisciplinary Graduate School for Environmental Research (HIGRADE). Additional thanks go to the Jörg Hausmann and Robert Nollau for excellent supporting during the field work and useful comments. Also, we thank the colleagues from the Centre de Recherche Public - Gabriel Lippmann: Dr. Laurent Pfister and Laurent Gourdol for administrative supporting.

Catchment parameters:Ÿ an area of 0.7 km²;Ÿ V-shaped valley;Ÿ valley slopes are mainly

forested (ca. 84%);Ÿ plateau surface is used by

agriculture (ca. 13%).

The outcrop representing the general geological sequence of study area:Ÿ soil surficial horizon;Ÿ periglacial deposits;Ÿ fractured schist;Ÿ compact schist.

Conclusions

Geophysical investigation along the selected hillslope:

Two-dimensional hillslope subsurface model in the terms of:Ÿ Geo-electrical investigation using ERT slope profile

(A) perpendicular to the Weierbach creek and VES-spreading (B) parallel oriented to the Weierbach creek in terms of electrical stratigraphic units (ESU s). The ’VES results for locations with lateral homogeneity perpendicular to the ERT profile are drawn with bold lines (a);

Ÿ Refraction seismic investigation (C) in terms of seismic velocity units (SVU s).’

Difference between VES and RS hillslope subsurface models (D) is ca. 2.6 m and is designated to a transition zone between periglacial deposits and fractured schist.

Box-whisker plots of resistivity (left graph) and thickness (right graph) destribution downhill as well as over the width of the investigated hillslope in terms of elementary functional units (EFU s).’

Sounding curves of measurements with Schlumberger and Half-Schlumberger arrays at ERT profile meter:

(a) 0 presenting an example for lateral homogeneity perpendicular to the ERT profile;(b) 75 presenting an example for lateral heterogeneity perpendicular to the ERT profile.

F Identification of three significant hillslope areas along the investigated hillslope in terms of EFU s;’F Determination of electrical and seismic stratigraphic units (ESU s and SVU s) with respect to the lithology of ’ ’the investigated study site;F Resistivity and seismic velocity hillslope models complement well one other.

The suggested approach provides a successful geophysi-cal investigation of the hillslope via combination of ERT, VES and RS in the efficient manner in contrast to the expensive 3D-measurements.

The test site is located in the north-west part of the Attert Baisn that lies in the contact zone between schistous Ardennes massif (Oesling) and the sedimen-tary Paris Basin (Gutland) in the mid-west of Grand-Duchy of Luxembourg.

European Geosciences UnionGeneral Assembly 2015

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Vienna | Austria | 12 - 17 April 2015

Pre-investigation cross to the hillslope using ERT to check the representation and homogeneity of the selected hillslope directly in the field.

Aim: Hillslope characterization in terms of functional units in a catchment using geo-physical methods in the efficient manner at a single profile.

Ÿ Hillslope as a functional landscape unit requires characterization of typical class members;

Ÿ The combination of electrical resistivity tomography (ERT) and refraction seismic (RS) for capturing lateral variability, and vertical electrical soundings (VES) for capturing the layering ;

Ÿ Schlumberger and Half-Schlumberger array to capture perpendicular to the homogeneityhillslope;

Ÿ Quantification of ambiguities in the interpretation of the geophysical data.

Geophysical description of the hillslope model in terms of

electrical and seismic units

Research questions:- typical for a investigated study site?- homogeneous?

Geophysical data acquisition

ERT VES

Data processing and interpretation

1D models2D model

Structural comparison of models

RS

3D

T

A

S

K

S

H y ld or - go ig se to s

GEOPHYSICIST

Research object

no

2D

Catchment characterizationin terms of landscape units

Selection of a reasonablerepresentative landscape unit

Test-measurement cross to the selected unit

Measurements along the selected unit

yes

1D

Flow chart for efficient geophysical investigation

see right diagram

Data interpretation as a multi-disciplinary result set

Introduction & Research philosophy

Selected representative landscape unit: A hillslope in the Weierbach catchment

Inversion result of the measure-ments at ERT profile meter 0 with equivalent models

J Typical for investigated areaJ Homogeneous: horizontal layering and nearly lateral invariable

Digital elevation model of the selected hillslope with measuring layout to combine geoelectrical and refraction seismic techiques.

a b

A

B

C

D

a b a

Results of Geophysicist’ tasks

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