Imaging fault geometry to learn
about earthquake mechanics
Phillip G Resor
Wesleyan University
Vanessa Meer, Giulio Di Toro, Ashley Griffith
Fault zones record an integrated
history of fault slip
Fault geometry and earthquakes:
the seismological record
Geometry and kinematics
of exposed fault surfaces
Looking inside rocks to
see the frozen record of
ancient earthquake
Slip during earthquake rupture is
heterogeneous
Observed in surface
ruptures
Treiman et al., 2002, BSSA
And inversions of
seismological and
geodetic data
Mai and Beroza, 2002, JGR
Slip heterogeneity is attributed to
asperities and barriers
Rheological: fault zone
materials
Shipton and Cowie, 2001, JSG
Geometrical: Slip
surface geometry
Fault Analysis Group
Fault geometry effects
earthquake dynamics
Km-scale discontinuities:
earthquake initiation,
termination, near fault stress
Wesnousky, 2006, Nature
Small-scale slip-perpendicular
roughness: frictional properties,
near fault stress
Sagy and Brodsky, 2009, JGR
Fault surfaces are characterized by
a suite of slip-parallel features
Corrugation axis
Tool Track
Slickenside
lineations
Gutter
Hancock and Barka, 1987, JSG
Fault surface roughness is
fractal (self-affine) in nature
linear decay of
the power
spectrum with
slope of 1+2H
dz -> lHdz
0≤H<1
Dixie Valley Fault
Candela et al, 2011, BSSA
dz
dx -> ldx
Power et al, 1987, EPSL
TLS and other technologies have led to a
renaissance in fault surface analysis
Photo: Emily Brodsky
Sagy et al, 2007, Geology
Brodsky et al, 2011, EPSL
Can we document effects of fault
topography on fault kinematics?
Resor and Meer, 2009 EPSL
Data
Collection
Surface
Morphology
Striation
Orientation
Visualizing
Surface
Morphology
Quantifying Morphology
Slip parallel
profiles
Spectral
Analysis
Slip perpendicular profiles
Resor and Meer, 2009 EPSL
Incremental slip varies across
the corrugated surface
Resor and Meer, 2009 EPSL
Fault normal and striation orientation are
correlated across the entire exposure
Striations
Fault Normals
Resor and Meer, 2009 EPSL
Spherical correlation,
significant at 99% probability
Observations from creeping faults
corroborate role of slip-parallel
features
Earthquake streaks on creeping faults are
slip-parallel independent of local geology
Rubin et al., 1999, Nature
Summary of work on exposed fault
surfaces
Fault surface exhibit self-affine scaling
over many orders of magnitude
Faults evolve (slowly)
toward smoother profiles
in the slip direction
Faults roughness
perturbs fault slip
direction
But, these results are derived from faults from <~5 km depth
Dynamic Rupture experiments reveal
a number of lubrication processes
Di Toro et al., 2011, Nature
Pseudotachylyte (frictional
melt) is the only unequivocal
evidence of earthquake
rupture velocities preserved
in fault zones
Pseudotachylyte-bearing fault
surfaces are not widely exposed
TLS and photogrammetry used to
image 3D geomtry of fault trace
Bistacchi et al, 2011, Pageoph
Roughness of pseudotachylyte-bearing
faults appears similar to small-slip faults
Self-affine scaling over
3-5 orders of magnitude
Smoother in slip
direction
Micro-roughness is critical to dynamic
slip and melt lubrication
Experiments reveal
that weakening
distance decreases
with increasing
normal stress
CT scanning
allows us to image
micro-scale
roughness of fault
surface
L05_07 core from extensional
fault bend
Griffith et al, 2010, JGR
Extensional bend surface roughness
due to fracture and wear
Griffith et al, 2010, JGR
L05_06 core from contractional
fault bend
Griffith et al, 2010, JGR
Contractional bend surface roughness
dominated by differential melting
Griffith et al, 2010, JGR
Conclusions and future directions
Exposed fault surfaces exhibit self-affine roughness
• Evolves with slip
• Perturbs incremental slip direction
• How is roughness generated?
Ferril et al., 1999, JSG
Sagy and Brodsky, 2009 JGR
Pseudotachylyte-bearing fault traces also exhibit selfaffine roughness at larger scales
• Fault zone geometry may be different
• Micro-roughness is controlled by melting
• Tie fault observations to experimental work
Slow to High Velocity Apparatus (SHIVA), INGV
“Rocks [melt] like butter in Rome” G. Di Toro
Corrugation axes are correlated
with long wavelength shape
Corrugation Axes
Fault Normals
Spherical correlation
significant at 99% probability