TY - GEN
T1 - The effect of geometrical irregularities on damage zone width
T2 - Modeling and field observations
AU - Tal, Yuval
AU - Faulkner, Daniel
PY - 2020/5/5
Y1 - 2020/5/5
N2 - Geological and geophysical observations of fault zones reveal that fault
cores are surrounded by regions of damaged rocks consist of fractures at
a wide range of length scales with decaying intensity with distance from
the fault core. The main mechanisms proposed for the development of
off-fault damage include slip on faults with geometrical irregularities,
migrating process zones, and dynamic damage from the passage of
earthquake ruptures. Field observations of relatively deep exhumed fault
zones have shown that fault damage zone width scales with the
displacement on a fault. In this study, we combine such observations
with numerical modeling to test what is the dominant mechanism producing
off-fault damage at depth of several kilometres.The field data [Faulkner
et al., 2011] include measurements of micro-fracture damage zone width
from small displacement fault zones within the Atacama fault zone in
northern Chile that formed at ∼6 km depth within a dioritic
protolith. An increase in damage zone width with displacement is clearly
seen. We perform simulations of slip on synthetic faults, with roughness
properties similar to that of natural faults, and examine how the total
slip and roughness characteristics affect the extent and intensity of
inelastic deformation to constrain the geometrical and frictional
properties that could generate the observed damage. To accurately
account for the effects of geometrical irregularities on the fault and
allow slip that is large relative to the size the minimum roughness
wavelength, we use the mortar finite element method, in which
non-matching meshes are allowed across the fault and the contacts are
continuously updated. Inelastic deformation of the bulk is modelled with
Drucker-Prager viscoplasticity, which is a simple choice for describing
cracked medium and is closely related to the Mohr-Coulomb model. Our
results indicate that, for the depth and fault lengths in the field
data, geometrical irregularities produce the scaling of damage zone
width with displacement observed in the field and suggest that this,
rather than the other mechanisms, produce most of the damage.
AB - Geological and geophysical observations of fault zones reveal that fault
cores are surrounded by regions of damaged rocks consist of fractures at
a wide range of length scales with decaying intensity with distance from
the fault core. The main mechanisms proposed for the development of
off-fault damage include slip on faults with geometrical irregularities,
migrating process zones, and dynamic damage from the passage of
earthquake ruptures. Field observations of relatively deep exhumed fault
zones have shown that fault damage zone width scales with the
displacement on a fault. In this study, we combine such observations
with numerical modeling to test what is the dominant mechanism producing
off-fault damage at depth of several kilometres.The field data [Faulkner
et al., 2011] include measurements of micro-fracture damage zone width
from small displacement fault zones within the Atacama fault zone in
northern Chile that formed at ∼6 km depth within a dioritic
protolith. An increase in damage zone width with displacement is clearly
seen. We perform simulations of slip on synthetic faults, with roughness
properties similar to that of natural faults, and examine how the total
slip and roughness characteristics affect the extent and intensity of
inelastic deformation to constrain the geometrical and frictional
properties that could generate the observed damage. To accurately
account for the effects of geometrical irregularities on the fault and
allow slip that is large relative to the size the minimum roughness
wavelength, we use the mortar finite element method, in which
non-matching meshes are allowed across the fault and the contacts are
continuously updated. Inelastic deformation of the bulk is modelled with
Drucker-Prager viscoplasticity, which is a simple choice for describing
cracked medium and is closely related to the Mohr-Coulomb model. Our
results indicate that, for the depth and fault lengths in the field
data, geometrical irregularities produce the scaling of damage zone
width with displacement observed in the field and suggest that this,
rather than the other mechanisms, produce most of the damage.
U2 - 10.5194/egusphere-egu2020-5884
DO - 10.5194/egusphere-egu2020-5884
M3 - Conference contribution
VL - 22
SP - 1
EP - 1
BT - EGU Online 4-8 May 2020
ER -