Auxiliary Material for
Seismic moment tensor and b-value variations over successive seismic cycle in laboratory
stick-slip experiments
Grzegorz Kwiatek1, Thomas Goebel2 and Georg Dresen1
1. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences,
Department 3: Geodynamics and Geomaterials, Section 3.2: Geomechanics and
Rheology, Telegrafenberg, D14473 Potsdam, Germany;
2. California Institute of Technology CALTECH, Seismological Laboratory, 1200 E.
California Blvd., MS 252-21 So. Mudd Building, Rm 262, Pasadena, CA 91125)
Geophysical Research Letters, 2014
Introduction
This supplementary material contains additional figures and thin sections photos useful in
understanding the relations between micromechanical processes occurring in investigated
samples during stick-slip friction experiment and acoustic emission response and its
characteristics (moment tensors, b-values).
Figure S1. Model of tensile earthquake (adapted from Vavryčuk [2001]). The tensile angle 

is the angle between slip vector u and its projection on the fault plane. The normal vector is


shown as n . For a pure shear faulting, the angle between P axis and normal to the fault n (or

slip vector u ) is 45° (   0 ), for shear faulting with compaction component this angle is
larger than 45° (   0 , ISO<0, CLVD<0) and finally for shear faulting with extension
component the same angle is smaller than 45° (   0 , ISO>0, CLVD>0), see Kwiatek and
Ben-Zion [2013] for corresponding P and S wave radiation patterns.
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Figure S2. Photo of the damage zone in S2cut sample displaying the fault topography is much
smoother in the saw-cut sample. The cumulative slip on this plane resulted in the creation of
a thin (<2 mm) gouge layer likely related to the fracture of fault asperities.
Figure S3. a) Spatial distribution of fault planes of AEs calculated from deviatoric part of the
MTs for the saw-cut sample S2cut (the plane was selected based on its proximity to
macroscopic fault plane). Orientations of the fault planes calculated from the deviatoric part
of the moment tensors b) Same fault planes together with the directions of P axes (cf. Fig 4)
showing steep P axis plunges.
Figure S4. Frequency-magnitude distribution for rough surface sample (cf. Fig. 3a in the
manuscript). The distribution follows clearly the power-law behavior.
Figure S5. a) Comparison of frequency-magnitude distributions for post- and pre-slip periods
for rough surface sample S1frac (cf. Fig. 3a). The post-slip periods are characterized by
increased AE activity. b) Dependence between AE magnitude and percentage of ISO
component (cf. Fig. 3b). No significant change in non-DC components is observed with AE
magnitude. Note that the AE magnitude is specific to the here employed transducers and is
not calibrated in an absolute sense.
Figure S6. Schematic representation of a shear-dominated micro-crack (a) and a micro-crack
that shows both compaction and shear contribution in the corresponding MTs (b). Note the
tensile angle is measured relatively to the fault plane whereas the P plunge is defined with
respect to the coordinate system of the sample as an angle between P axis direction and plane
perpendicular to the loading axis.
Figure S7. Photo of the damage zone developed in rough surface sample S1frac. Progressive
sliding along the fault with pronounced topography involves dilation and compaction of the
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fault zone and shearing along the anastomosing and localized slip bands within the fault
damage zone.
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