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Étude in-situ des interactions hydromécaniques entre fluides et failles Application au laboratoire du rift de Corinthe. Ð O À N Mai Linh Institut de Physique du Globe de Paris. Fault slip. Fluid pressure Build-up. Fluid Pressure decrease. Fluid-fault interactions.

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Ð O À N Mai Linh Institut de Physique du Globe de Paris

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O n mai linh institut de physique du globe de paris

Étude in-situ des

interactions hydromécaniques

entre fluides et failles

Application au laboratoire du rift de Corinthe

ÐOÀN Mai Linh

Institut de Physique du Globe de Paris


Fluid fault interactions

Fault slip

Fluid pressure

Build-up

Fluid Pressure

decrease

Fluid-fault interactions

Example of fluid-fault hydromechanical coupling:

Fault-valve mechanism (Sibson70)

Fault closed


Motivations

Lots of

theory and

laboratory

works

Motivations

  • But field data:

  • altered outcrops

  • after slip

  • dynamical seismics

  • indirect

After Matthai (1992)


Structure of the presentation

Structure of the presentation

I Presentation of the Gulf of Corinth

and the DGLAB project

II Characterization of the hydraulic setting

III A peculiar kind of hydraulic transients:

Events triggered by far earthquakes

I Presentation of the Gulf of Corinth

and the DGLAB project

II Characterization of the hydraulic setting

III A peculiar kind of hydraulic transients:

Events triggered by far earthquakes


The corinth rift

subduction

shear zone

extension

Rift of Corinth

Pindos

Gavrovo-

Tripolitza

The Corinth Rift

Greece

Complicated

geodynamics

Complex

geology

From Jolivet (2005)


The corinth rift1

1.5cm/yr

Aigio fault

1-3cm of slip

After Koukouvelas (1998)

The Corinth Rift

After Bernard (1997)


D eep g eodynamic lab oratory

0.9±0.1MPa

karst

Deep Geodynamic LABoratory

South

North

0.5±0.1MPa


Initial hydraulic knowledge of the aigio fault

  • Laboratory test on core samples

K=0.9-2 10-18m²

(Song,2004)

  • Difference in mineralization

Initial hydraulic knowledge of the Aigio fault

Impervious fault

  • Difference in overpressure


Initial hydraulic knowledge of upper aquifer

(Giurgea, 2004)

Double porosity model

Results to

be taken

with caution

Bulk properties

Matrix properties

Initial hydraulic knowledge of upper aquifer

Drawdown [m]

Hydraulic tests by GFZ – July 2003


Initial hydraulic knowledge of the karst

Permanent regime 

Dupuit formula

Q~600m³/h

Initial hydraulic knowledge of the karst

k=1-1.5 10-5 m/s

No storativity


Aig10 permanent sensors

AIG10 permanent sensors


Pressure sensors

Pressure sensors

Tides

Log10(Pressure [MPa])

2 absolute pressure gauges

- high precision

- low precision

1 relative pressure gauge

- hydrophone

Log10(Frequency [Hz])


Structure of the presentation1

Structure of the presentation

I Presentation of the Gulf of Corinth

and the DGLAB project

II Characterization of the hydraulic setting

III A peculiar kind of hydraulic transients:

Events triggered by far earthquakes


Quality of the pressure signal

Quality of the pressure signal

Pressure

Pressure (Bar)

UT Time

Resolution better than 1%

The pressure is similar to that of the karst

The karst dominates the measured pressure


Strategy

Strategy

Tidal

calibration

Tidal

calibration

Long-term

fluctuations

How sensitive is the pressure signal to deformation ?

What are the

dimensions

of the aquifers ?

How water

flows through

the aquifers ?

Thermal

Regime


Tidal inversion

Trizonia

  • Oceanic load

  • (P. Bernard)

(Aigio)

Temeni

Also

  • Barometric pressure

  • (V. Léonardi)

Tidal inversion



Triple origine

  • Earth Tide

  • (Prediction ETERNA 3.3)

Aigion


Analysis of the tidal signal

Analysis of the tidal signal

Linear regression on the input data

Ouput: pressure in Aigio

Input: Tide gage in Trizonia

Input: Barometric pressure in Temeni

Input: Theoretical tidal strain in Aigio


Analysis of the tidal signal1

Analysis of the tidal signal

dP=2.748 10-4 dhoc – 1.784 10-4 dter

No offset


Barometric effect

Barometric effect

Bad weather at the end of the year 2003

Observed pressure (detided)Û Atmospheric pressure


Interpretation of the coefficients

Interpretation of the coefficients

Poroelastic model (large wavelengths)

B : Skempton coefficient

Ku : Undrained bulk modulus

u : Undrained Poisson ratio

 : Barometric efficiency

=0.3±0.1

B Ku=17±1GPa


Oceanic load

Water flux

Oceanic load

S

Aig10

N

¯¯ Oceanic load ¯¯

Loading profile at a depth of 700m induced by a unit load

σxx+σzz/2ρgh

AIG10

Distance to southern shore (m)

The oceanic load should induce a phase lag !


Influence of boundaries

Influence of boundaries

S

Aig10

N

¯¯ Oceanic load ¯¯

Aigio

fault

Helike

fault

Can the presence of impervious faults explain

this absence of phase lag ?

Analytical prediction of phase lag

for a 1D aquifer with impervious boundaries


Oceanic load1

S

N

N

Oceanic load

Map of semi-diurnal phase lag (°) for a semi-infinite ocean

Phase lag

[-5 min 5min]

ß

[-2.5° 2.5°]

L

x/L


Is aigio fault impervious at all depths

Is Aigio fault impervious at all depths ?


Tidal information

Tidal

calibration

Long-term

fluctuations

Tidal information

Tidal

calibration

Tidal

calibration

Long-term

fluctuations

How sensitive is the pressure signal to deformation ?

Poroelastic parameters

→ excellent « strain » sensor

Karst confined

in a NS direction.

By Aigio fault ?

What are the

dimensions

of the aquifers ?

Storativity

→ Hydraulic

diffusivity

How water

flows through

the aquifers ?

Thermal

regime


Long term data

Long-term data

Pressure

Flow between

the two

previously

independent

aquifers

No

sharp

seasonal

variations

14 kPa

Pressure (bar)

Time

1 year


Analytical solution

Axisymmetric response for infinite aquifers

Pressure (bar)

Time (day)

Analytical solution

Axisymmetric analytical solutions

 Finite aquifers

 Transients controlled by the radii of the aquifers and borehole radius


Development of the fem2 1d method

Development of the FEM2.1D method

1. Finite Element Method 2D

to describe flow

in upper and lower aquifers

2. Manual coupling at a

well node (0.1D)

Same pressure

Mass conservation of fluid

  • Efficient

  • Keep the characteristic

    distance of the well radius


Dimensions of the aquifers

Dimensions of the aquifers ?

Can the decrease in pressure observed during the first 3 months

provide constraints on the dimensions of the aquifers ?

Rectangular-shaped aquifers 4 unknowns

Hydraulic properties of the upper aquifer 1 unknown (storativity)

2 pieces of information to fit : amplitude and duration of the drop

Try to find plausible configurations


Dimensions of the aquifers1

Too small

Too slow

Dimensions of the aquifers ?

Upper aquifer: LNS=1000m LWE=200m

Lower aquifer: LNS=5000m LWE=?

Pressure (bar)

Pertinence of

The homogeneous

Model for the karst ?

Time (days)


Long term information

Long-term

fluctuations

Thermal

regime

Long-term information

Tidal

calibration

Tidal

calibration

Long-term

fluctuations

Poroelastic parameters

→ excellent « strain » sensor

Karst confined

in a NS direction

Both aquifers

are confined

Hydraulic

diffusivity

(Almost) no flow

Storativity

→ Hydraulic

diffusivity

Thermal

Regime


Thermal profile

Thermal profile

1 year

after drilling

Temperature (°C)

Depth (m)


Heat flow measurement

=

Heat flow measurement

50±10 mW/m2

~22°C/km


Karst convection

zt

Tt

770m

Tmes

H>600 m

 Gavrovo-Tripolitza nappe

Karst convection

Fault vertical offset=150m

zt-770m  <150m

qb= 70mW/m²

qb=100mW/m²

qb=200mW/m²

Relation Ttzt

from extrapolation of

Thermal gradient

H > 400 m


Thermal anomaly

Temperature (°C)

30

30.2

30.4

30.6

30.8

31

31.2

31.4

31.6

31.8

700

But the introduction of the

karst convection does.

710

720

Depth (m)

500

730

Karst in

conduction

1000

740

Karst in

convection

1500

0

10

20

30

40

50

60

Temperature (°C)

Thermal anomaly

Heat generated by fault slip

does not explain this anomaly


Thermal information

Thermal information

Tidal

calibration

Tidal

calibration

Long-term

fluctuations

Poroelastic parameters

→ excellent « strain » sensor

Hydraulic

diffusivity

Internal advection

Hydraulic

diffusivity

(Almost) no flow

Both aquifers

are confined

Both aquifers

are confined

Large vertical extension

Thermal

regime

Low heat flow

50±10 mW/m²


Structure of the presentation2

Structure of the presentation

I Presentation of the Gulf of Corinth

and the DGLAB project

II Characterization of the hydraulic setting

III A peculiar kind of hydraulic transients:

Events triggered by far earthquakes


A panel of hydraulic anomalies

A panel of hydraulic anomalies

~10minute-long

~2minute-long

10-200 Pa

10-200 Pa

~100 events/yr

~20 events/yr

Pressure

~2minute-long

~30minute-long

10-400 Pa

50-60 Pa

~200 events/yr

2 events/yr

Only associated with

teleseismic transients

Time


The m w 7 8 rat island earthquake

Much earlier than

other published

triggered events

The Mw=7.8 Rat Island Earthquake

November, 17th 2003

06:43 UTC

Drop of 60 Pa

(equivalent to 3.5nstr)

BKu~17GPa

determined from tidal analysis

30min

5min


Review of triggered hydraulic anomalies

Review of triggered hydraulic anomalies

Strain>10-8

2003

Rat Island

Event

Magnitude

Strain<10-8

Distance to epicenter (km)

After Montgomery and Manga (2003)


Comparison with other local sensors

Anomalous drop on pressure data only

h<5nstr

Comparison with other local sensors

Trizonia

Aigio

LF signal

0 10km

Sacks-Evertson

Strainmeter

STS2

broad-band

Seismometer

(North component)


Validity of the pressure data

Validity of the pressure data

Comparison of seismic oscillations

of both «deformation» sensors

Nyquist frequency

of the pressure

sensor

P

Frequency

h

- Strainmeter

- Pressure

Good correlation of both sensors

Time


Response to a dislocation

Response to a dislocation

One single wellhead value

Average of pressure

anomaly

along the borehole

Poroelastic response

HETEROGENEOUS

along the borehole

Fault movement


Response to a dislocation1

Response to a dislocation

Average of pressure along the borehole

induced by a double-couple located at (x,y)

M0=DS

Map of Log10(Pressure anomaly) for D×S=1m3

x

y

S= slip area

D= relative displacement

Dip direction

z

x

y

Distance from borehole

~ √hydraulictrelaxation

D×S~1m3

<5000m3 (Trizonia data)


High frequency hydrophone data

High-frequency hydrophone data

Hydrophone

Close-up

Pressure

UTC Time 07:07:02

07:15

07:10

07:05

07:05

07:10

07:15

Hydrophone

+0.000

+0.100

07:05

07:10

07:15

Time


Angle of slip

Average of pressure along the borehole

induced by a double-couple located at (x,y)

Map of Log10(Pressure anomaly) for D*S=1m3

Not seen by pressure sensor D*S<0.1-1m3

Angle of slip

z

x

x

y

y

Fault plane

Slickensides


The m w 9 sumatra event

Below Nyquist frequency

The Mw=9 Sumatra event

Data acquisition problem Irregular sampling

Pressure

in Aigio

December, 26th 2004

00:58 UTC

P

S

Strain

in Trizonia


Conclusion

Conclusion

Hydraulic characterisation of AIG10

  • We measure the pressure of the bottom karst

  • Poroelastic response to both Earth tides and ocean load

    ÞSensitive “strain” sensor

  • Aquifers are confined with almost no flow at the boundaries

    and internal convection within the karst

  • Aigio fault is impervious at the intersection with the borehole

    but is it the case below the Pindos nappe

  • Low heat flow

Hydraulic characterisation of AIG10

It is now possible to model

the wellhead pressure response to

fault movement

within an homogeneous poroelastic framework

Hydraulic anomalies

The DGLAB project provides the opportunity

to study

dynamic fluid-fault interactions

Hydraulic anomalies

  • A large set of hydraulic anomalies.

  • An anomalous hydraulic anomaly

    dynamically triggered by S waves from a teleseism,

    with a concomitant local microseismic event


Perspectives

Perspectives

Interpretation of the remaining hydraulic events

  • Better knowledge of the surrounding seismicity

  • Better interpretation of the hydrophone signal

  • Better understanding of the aquifer and its heterogeneities

  • But we monitor fluids around a fault

  • rather than fluids inside a fault

  • But no independent evaluation

  • of fluid evolution and fault movement


Perspectives1

Perspectives

Expected full instrumentation

0 m

Hydrophone

Installation of the

whole instrumentation

scheduled in

March 2006

Hydrophone

700 m

High-precision

pressure gage

750 m

High-precision

pressure gage

870 m

3C Seismometer

1000 m


Link between storativities

Link between storativities

S = uniaxial storativity11= 22=0, d33=0

S = unstrained storativity =0

S = strained storativity d=0

S SS

S= (1-αB) S


The aig10 borehole

0.9±0.1MPa

karst

The AIG10 borehole

0.5±0.1MPa


Age of the karst water

Age of the karst water

Simple optimistic model :

Čermák model

T>1000 yr

(In accordance

with the absence of

Tritium in water)


The lower aquifer is karstic

The lower aquifer is karstic

900

800


Are the aquifers well confined

Are the aquifers well confined ?


All the three studies were necessary

All the three studies were necessary

Tidal

calibration

Tidal

calibration

Long-term

fluctuations

Thermal

regime


Pressure sensors1

Pressure sensors

Tides

Log10(Pressure [MPa])

2 absolute pressure gauges

- high precision

- low precision

1 relative pressure gauge

- hydrophone

Log10(Frequency [Hz])


Development of the fem2 1d method1

Development of the FEM2.1D method

Analytical axisymmetric solutions

shows that the transitory regime

is partly controlled by

the borehole radius

1. Finite Element Method 2D

on each aquifer

2. Manual coupling at a

well node (0.1D)

  • Efficient

  • Keep the characteristic

    distance of the well radius


Conclusion1

Conclusion

Hydraulic characterisation of AIG10

  • We measure the pressure of the bottom karst

  • Poroelastic response to both Earth tides and ocean load

    ÞSensitive “strain” sensor

  • Aquifers are confined with almost no flow at the boundaries

    but internal convection within the karst

  • Aigio fault is impervious at the intersection with the borehole

    but is it the case below ?

  • Low heat flow and rigid block. Not a process zone.

Hydraulic anomalies

  • A large set of hydraulic anomalies.

  • A anomalous hydraulic anomaly

    dynamically triggered by S waves from a teleseism,

    with concomitant a local seismic event

  • Borehole instrumentation provides tools

  • to understand the triggering mechanism


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