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Kombineret inversion af MEP og seismik data med boringsoplysninger som á priori Combined inversion of MEP and seismic data with drilling data as prior information. Roger Wisén 1 , Anders Vest Christiansen 2 , Esben Auken 2. Lunds Tekniska Högskola, Sverige

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Roger wis n 1 anders vest christiansen 2 esben auken 2

Kombineret inversion af MEP og seismik data med boringsoplysninger som á prioriCombined inversion of MEP and seismic data with drilling data as prior information

Roger Wisén1, Anders Vest Christiansen2, Esben Auken2

  • Lunds Tekniska Högskola, Sverige

  • GeoFysikSamarbejdet, Aarhus Universitet

Tack till:

CityTunnelProjektet och

Nordisk Forskerutdanningsakademi


Disposition

Introduction to the case boringsoplysninger som á priori

Geology and hydrogeology of the investigated area

Aim of the investigation

Part 1 – Combined interpretation of resistivity models from 2D smooth inversion and 2D-LCI

Part 2 – Combined inversion of seismic and resistivity data

Summary

Disposition


Railway trench in Malmö, Sweden boringsoplysninger som á priori


Map of the investigated area
Map of the investigated area boringsoplysninger som á priori


Geology och hydrogeology

  • Postglacial sediments

  • Clay till

  • Intermorainic sediments

  • Limestone


Aim of the investigations boringsoplysninger som á priori

  • Problem:

  • Inflow of groundwater from the limestone or intermorainic sediments during construction of the trench

  • The effects can be reduced if risk areas are known in advance

  • Aim:

  • Map depth to limestone

  • Map extension, thickness and composition of intermorainic sediments

Trench


Multi electrode profiling mep
Multi Electrode Profiling - MEP boringsoplysninger som á priori

  • Combination of Wenner and Schlumberger measurements

  • 2 m minimum electrode separation

  • About 25-30 m depth penetration


Disposition1

Introduction to the case boringsoplysninger som á priori

Geology and hydrogeology of the investigated area

Aim of the investigation

Part 1 – Combined interpretation of resistivity models from 2D smooth inversion and 2D-LCI

Part 2 – Combined inversion of seismic and resistivity data

Summary

Disposition


Profile along the planned trench boringsoplysninger som á priori

Pseudo-section

2D smooth inversion

2D LCI

Residuals


Profile along the planned trench boringsoplysninger som á priori

2D LCI

2D LCI with prior data


Disposition2

Introduction to the case boringsoplysninger som á priori

Geology and hydrogeology of the investigated area

Aim of the investigation

Part 1 – Combined interpretation of resistivity models from 2D smooth inversion and 2D-LCI

Part 2 – Combined inversion of seismic and resistivity data

Summary

Disposition


Multichannel analysis of surface waves masw

………………….. boringsoplysninger som á priori

VPh (m/s)

Seismic source

Geophones

FFT

f (Hz)

VS(m/s)

VPh(m/s)

Primary model parameters:

Vs – Shear wave velocity [m/s]

T – Lagertjocklek [m]

Secondary model parameters:

Ny – Poisson’s ratio [m]

Rho – Density [kg/m3]

Invers modelling

Dispersion-curve

Velocity-modell

Depth(m)

f(Hz)

Multichannel Analysis of Surface Waves - MASW


Combined lci on resistivity and seismic data
Combined LCI on boringsoplysninger som á prioriresistivity and seismic data


Combined lci on seismic and resistivity data
Combined LCI on boringsoplysninger som á prioriseismic and resistivity data

LCI on resistivity data

Separate LCI on seismic and resistivity data

Combined LCI on seismic and resistivity data


Summary part 1

Smooth 2D inversion provides high lateral resolution boringsoplysninger som á priori

2D-LCI provides sharp layer boundaries

The combined interpretation of the two resistivity models increase the possibility to make a precise geological interpretation

The use of a large amount of prior information in 2D-LCI, without increase of the data residual error, gives great confidence in the resistivity data

The prior information helps solving equivalence problems and decreasing 3D effects

The geological interpretation points out a few important features

The limestone level in the eastern part of the profile is very close to the planned bottom of the trench

Intermorainic sediments with large lateral extension coincide with the planned position of the trench

In some areas these sediments are high resistive and therefore expected to have high hydraulic permeability

Further investigations, mainly test pumping and construction of test pits, have already been started

Summary – part 1


Summary part 2

Combined inversion of resistivity and seismic data functions very well in this case

The seismic model is improved for the combined inversion

Depths to layers in the velocity model gets better determined when inverted together with resistivity data...

... which results in better determined velocities

With more seismic data available combined inversion could help to solve high resistive equivalence problems

Summary – part 2


Resultat från resistivitetsmätningar very well in this case

Tvärprofil


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