3D modelling of fault-zone architecture along a major ... · 3D modelling of fault-zone architecture along a major Alpine wrench lineament: the Pusteria and Sprechenstein-Mules fault

3D modelling of fault-zone architecture along a major Alpine wrench lineament: the Pusteria and Sprechenstein-Mules fault system

Andrea Bistacchi, Matteo Massironi & Luca Menegon

1. How to build a computer model of fault-zone architecture?to model geometry and properties

topology of the model should reflect fault-zone architecture

geomodelling technology from the oil industry gOcadgeom

odel

ling

> overview

1. How to build a computer model of fault-zone architecture?need to model geometry and propertiestopology of the model should reflect fault-zone architecture geomodelling technology from the oil industry gOcad

2. Case studied: the Pusteria and Sprechenstein-Mules fault systemdataset: field geology and boreholes (from a deep tunnelling project)dextral (reverse) fault system with contractional stepovers

PF

-SM

F s

yste

mge

omod

ellin

g> overview

borehole data: > 2000 mcontinuous core and geophysical

log data across the fault zone

contractional stepover

> overview

1. How to build a computer model of fault-zone architecture?

need to model geometry and properties

topology of the model should reflect fault-zone architecture

geomodelling technology from the oil industry gOcad

2. Case studied: the Pusteria and Sprechenstein-Mules fault system

dataset: field geology and boreholes from a tunnelling project

strike slip fault system with contractional stepovers

3. Why a computer model of fault-zone architecture could be useful?visualization, understand complex structures, …

output realistic quantitative geometry and properties to mechanical models, fluid flow models, etc.

geom

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PF

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> how to build a computer model of fault-zone architecture?

gOcad topology and interpolation (CAD and geostats coupled)

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[Mallet, 2002]

n functions φn(α), ∀ α∈Ω

graph Ģ(Ω,N) linear constrains C

discrete model Mn(Ω,N,φ,C)

P(A)

A



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topology of a natural object A is approximated using a cellular partition model P(A) based on the GMaps algebraic structure

hierarchical embedded objects lines (n=1), surfaces (n=2), solids (n=3) [Mallet, 2002]

nodes neighborhood



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first three components of φn(α) define spatial coordinates at all nodes α of the discrete model: φx(α), φy(α), φz(α)

other n-3 components define any other continuousor categorical property: attitude of a surface (gradient), degree of fracturing, porosity, seismic impedance, density, lithology, age, etc.

any property can be calculated at any point by linear interpolation ( similar to FEM mesh) [Mallet, 2002]



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property functions φn are simultaneously interpolated based on available data (constraints)

C= hard equality constraints - to be honoured strictly

C≈ soft equality constraints – to be honoured in a least square sense

C> (hard) inequality constraints

Discrete Smooth Interpolator (DSI) interpolates φn based on

C = C= U C≈ U C> and “minimum local roughness” criterion [Mallet, 2002]



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discrete fault zone architecture model (DFZAM) fault surface network and surrounding volume (damage zone), modelled with hierarchical fully coupled topology, integrating all data from field and subsurface geology

> the Pusteria (PF) & Sprechenstein-Mules (SMF) fault systemP

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PF is the eastern segment of the Periadriatic lineament, one of the largest (>600 km) faults in the Alps. SMF is a younger dextral lineament, connecting the PF to the Brenner detachment

PFPF

SMFSMF

Bre

nner

Bre

nner

[Bigi, 1992; Castellarin, 2004]


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PF is the eastern segment of the Periadriatic lineament, one of the largest (>600 km) faults in the Alps. SMF is a younger dextral lineament, connecting the PF to the Brenner detachment

PFPF

SMFSMF

Bre

nner

Bre

nner

[Bigi, 1992; Castellarin, 2004]


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PF is the eastern segment of the Periadriatic lineament, one of the largest (> 600 km) faults in the Alps. SMF is a younger dextral lineament, connecting the PF to the Brenner detachment

[Massironi, 2004]


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[Massironi, 2004]


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PFPF

SMFSMFBrixen Granite (non-metamorphic footwall)Brixen Granite (non-metamorphic footwall)

Tonalitic “Lamella”(sheet-like pluton - 30Ma)

Tonalitic “Lamella”(sheet-like pluton - 30Ma)

Austroalpine Gneiss (Alpine metamorphism)Austroalpine Gneiss (Alpine metamorphism)SMFSMF

PFPF


[Massironi, 2004]

hangingwallhangingwall


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Time & temperature constraints:

o Brixen Granite (footwall) always below 150-200°C in the Tertiary.

o Tonalitic Lamella emplaced at 30 Ma at about 450°C – 15 km, then exhumed with its host rock, the Austroalpine basement. The two hangingwall units cooled below ca. 250°C at 24 Ma. [Bistacchi, in prep.]


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Time & temperature constraints:

o Brixen Granite (footwall) always below 150-200°C in the Tertiary.

o Tonalitic Lamella emplaced at 30 Ma at about 450°C – 15 km, then exhumed with its host rock, the Austroalpine basement. The two hangingwall units cooled below ca. 250°C at 24 Ma. [Bistacchi, in prep.]

Kinematics: dextral with thrust component since 30 MaKinematics: dextral with thrust component since 30 Ma

> fault network (FN) and tectonic unit boundaries model: geometryP

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field geology & borehole data 8km x 4 km x 1.5 km 3D model

[Bistacchi, 2007]


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[Bistacchi, 2007]



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[Bistacchi, 2007]


topology of FNtopology of FNconstraintsconstraints

interpolationinterpolation


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[Bistacchi, 2007]

> properties: 1- fault cores (preliminary characterisation)P

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fault core relatively thin layers (1-5 m?) of mature fault rocks, developed generally in correspondence of major tectonic boundaries and master faults, where much of the displacement is achieved

Brixen Granite Tonalitic Lamella &Austroalpine basement

5-10 m protocataclasite(ultra-) cataclasite along PSZs (dm-m)

thick greenschist facies phyllonites (pre-brittle faults) reactivated by frequent

PSZs (cm-m) with foliated ultracataclasite and polished SSs


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5 µm


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> properties: 2- damage zonesP

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damage zone how to (semi-) quantitatively map “damage” (40 km2)?

1m x 1m square window1m x 1m square window

towards fault core


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damage zone how to (semi-) quantitatively map “damage” (40 km2)?

Fd = cumulative fracture length/areaNj = number of joint setsFd = cumulative fracture length/areaNj = number of joint sets

Fd = 11.263 m-1

Nj ≤ 3Class 1

Fd = 11.263 m-1

Nj ≤ 3Class 1

Fd = 13.118 m-1

Nj ≤ 3Class 1

Fd = 13.118 m-1

Nj ≤ 3Class 1

Fd = 18.511 m-1

Nj = 4÷5Class 2

Fd = 18.511 m-1

Nj = 4÷5Class 2

Fd = 23.653 m-1

Nj > 5Class 3

Fd = 23.653 m-1

Nj > 5Class 3

Fd = n.d.Nj = n.d.Class 4




towards fault core


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damage zone how to (semi-) quantitatively map “damage”?

GISborehole

log

Nj class.

DSI interpolation

damagemodel

Nj class.

Interpolation on a 3D regular grid (voxet).Grid connectivity broken across faults

(topology of the model reflects fault zone architecture).


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damage zone how to (semi-) quantitatively map “damage”?

GISborehole

log

Nj class.

DSI interpolation

damagemodel

Nj class.

Interpolation on a 3D regular grid (voxet).Grid connectivity broken across faults

(topology of the model reflects fault zone architecture).

FAULT

> discrete fault zone architecture model (DFZAM)P

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> conclusionP

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1. Discrete model of fault zone architecture:dependence of damage zone thickness from fault network geometry (curvature, stepovers) and lithology has been verified

a new framework for damage zone characterization has been proposed (need to be further verified)

damage zones around stepovers are highly fractured “columns” hydraulic conduits

2. Why a computer model of fault-zone architecture could be useful?visualization, understanding complex structures

quantitative analysis of geometry (e.g. differential geometry) made easy

build realistic model of geometry and propertiesthat can be output to, and quantitatively compared to mechanical models, fluid flow models, etc.

BBT SE is acknowledged for giving access to > 2000 m of continuous core and borehole logging data of the Brenner Basistunnel project

ASGA, Earth Decision Sciences and Paradigm are thanked for welcoming Padova and Milano Bicocca Universities in the gOcad Research Consortium

… thank you!

Documents

3D modelling of fault-zone architecture along a major ... · 3D modelling of fault-zone architecture along a major Alpine wrench lineament: the Pusteria and Sprechenstein-Mules fault