Fault activation and microseismicity in laboratory

experimentsThomas Göbel

Danijel Schorlemmer, Sergei Stanchits, Erik Rybacki

Georg Dresen, Thorsten Becker, Charles Sammis

1. Changes in spatial and size distributions of seismic events during fault reactivation

2. What type of seismic sources do we expect?

3. Future experiments

Sample and sensors

Rock specimen with notches

Pressure vessel and loading frame

Acoustic emission system:

o 16 channelso 10 MHz sampling frequencyo 16 bit resolutiono Piezo-electric sensors with

resonance frequency at 2MHzo Active and passive recordingo Full waveform recording

Loading curve during fault reactivation

Displacement (mm) Goebel et al. 2012

Waveforms of small and large events

Goebel et al. 2012

Typical AE event Large stress drop event

Goebel et al. 2012

Waveforms of small and large events

AE hypocenter locations

Goebel et al. 2013c

1. Spatial distribution and b-value

Lockner et al. 1991

Progressive failure

AE clustering at different stress levels

AE clustering at different stress levels

AE clustering at different stress levels

Cyclical changes of b-values and stress

Goebel et al. 2013a

Stress and b-values prior to slip events

Goebel et al. 2013a

2. Source mechanism

Fortin et al. 2009

Principle types of acoustic emission in porous media

Kwiatek & Goebel in prep.

Main source mechanism during stick-slip

Onset of slip event

Kwiatek & Goebel in prep.

Main source mechanism during stick-slip

Aftershock sequence

Moment tensors during slip event and aftershock sequence

Shear dominated

Kwiatek & Goebel in prep.

Thompson et al. 2009

Moment tensors of large magnitude events

Conclusion• b-values decrease during stress-increase

before fault activation in laboratory analog

• Fractal dimension close to 2 indicate fault related seismicity

• Slip instability is connected to shear-type seismic events

• Frequency content and amplitude spectra are sensitive to fluid content and loading

3. Future Experiments

Dresen et al. 2010Pp Pp Pp Pp

Dresen et al. 2010σ1

PcPc

σ1

Pp Pp Pp Pp

Dresen et al. 2010σ1

PcPc

σ1

σ1

Pc

σ1

Pp

Pc

Pp Pp Pp Pp

Dresen et al. 2010σ1

PcPc

σ1

σ1

Pc

σ1

Pp

PpPc

Pp Pp Pp Pp

Harrington & Benson 2011

Fluid induced eventsMicroseismicity in dry samples

No. Ch.

Thermally induced cracks vs. shear type events

Low frequency content, monochromatic spectrum

Burlini et al. 2007

- Thank You -

Additional Slides

Thermally induced cracks vs. shear type events

Low frequency content, monochromatic spectrum

Burlini et al. 2007

Thermally induced cracks vs. shear type events

Burlini et al. 2007

Self-similar scaling

Fluid induced eventsMicroseismicity in dry samples

Am

plitu

de

Am

plitu

deNo clear scaling

Harrington & Benson 2011

D = 2.75D = 2.66D = 2.25

Hirata et al. 1987

Creep tests at constant stress (547 MPa)~ 7 h to failure

Progressivefailure

Changes in fractal dimension with successive stick-slip events

Goebel et al. 2013b

Interslip Period Goebel et al. 2013b

Fractal dimension and fault smoothing

Frac

tal D

imen

sion

Shear dominated

Slip onset

Changes in source mechanism and orientation of principal stressdue to slip

Attenuation and changes in seismic velocityduring damage accumulation

Stanchits et al. 2003

Stanchits et al. 2003