Post on 01-Jan-2016
interseismic deformation with aseismic stress-dependent fault slip
Eric A Hetland, Mark Simons, Ravi Kanda, Sue Owen
TO brown-bag – 03 April 2007
a very informal, and preliminary talk about how we are thinking about
Hsu et al., 2006
post-seismic slip following subduction ruptures:
fault rheology is not (explicitly) included in after-slip model
2005 Nias-Simeulue eq. (M8.7)
Pritchard & Simons, 2006
post-seismic slip following subduction ruptures:
fault rheology is not (explicitly) included in after-slip model
1995 Antofagasta eq. (M8.1)
post-seismic slip following subduction ruptures:
fault rheology is not included in after-slip model
2003 Tokachi-oki eq. (M8)
Baba et al., 2003
inter-seismic slip near regions of past subduction ruptures:
Suwa et al., 2006
model assumes fault slip during inter-seismic period is constant
Japan/southern Kurile trenches
we want an internally consistent model we want an internally consistent model that can describe observations of both that can describe observations of both inter-seismic and post-seismic inter-seismic and post-seismic deformation…deformation…
for now we are building subduction zone models that include repeated ruptures, on assumed asperities, with stress-dependent aseismic slip on the non-asperity portions of the subduction interface during the interseismic period…
Baba et al., 2003 Suwa et al., 2006
L
elastic half-space
long-termfault-slip
U’ cuts 1/2-space
with fault loading:
traction on the faultfinite fault plane in
1/2-space
slip on the fault(Burgers vector)
includes theoff-fault rheology
with fault loading:
=0
e.g.; Rice, 1993; Liu and Rice, 2005.
Note: no seismic radiation damping (e.g., Rice, 1993) - there are no seismic waves & no problems with unbounded slip velocities in our models…
“back-slip”introduced by J. Savage (Savage and Burford, 1973; Savage and Prescott, 1978; Savage, 1983) as a mathematically convenient fault loading mechanism in kinematic & quasi-kinematic models
+ =
Savage & Burford, 1973; Savage & Prescott, 1978
Suwa et al., 2006
red = lots of BSwhite = no BS
approximation only good approximation only good for spun-up systems:for spun-up systems:
rate of interseismic relaxation= rate of reloading
tractionon fault
part of faultthat is allowed to
slip interseismically
part of fault withcoseismic slip
part of faultthat slipssteadily
interseismicslip on fault
imposedruptures at
times Tp
long-termfault-slip
we impose ruptures - we do not solve for them:
locked
-
’-
tractionon fault
interseismicslip on fault
imposedruptures at
times Tp
part of faultthat is allowed to
slip interseismically
part of fault withcoseismic slip
part of faultthat slipssteadily
long-termfault-slip
we impose ruptures - we do not solve for them:
non-linear viscous(Montesi, 2004)
RS-friction(e.g. Marone et al., 1991)
linear viscous
need a fault rheology:
Dieterich, 1979; Ruina 1983; Rice and Gu, 1983 (figure from Ben-Zion, 2003)
rate- and state-friction
(a-b)<0 “ruptures”, (a-b)>0 “aseismic slip”
is a state variable, assume it is constant = L/v
= N
Ben-Zion, 2003
Lapusta et al., 2000
we impose ruptures - we only solve for aseismic slip:
fault rheology:
bulk rheology:
given by for now, assume elastic half-space and use Okada, 1992
model works for 3D, non-planar faults, with multiple asperities, arbitrary rheologic
parameters, we allow both dip- and strike-slip co- and inter-seismic slip, and irregular
(imposed) rupture sequencescurrently, we can impose coseismic slip in non-locked regions of the fault, but we do not allow interseismic slip in the locked regions…
use boundary elements…
= 30 GPa
’N = 300 MPa
D = 104 m
bo = 10 m
(a-b) = -1/10
-1 = 0.5 (a-b) = 0.05
-1 = 1.0 (a-b) = 0.10
10D
D/2
Dlockedsection
steady slip
at depth
“thrust fault” in an elastic half-space, dipping 45 degrees
modification of ubiquitous subduction back-slip model, by allowing interseismic slip here
10D
D/2
Dlockedsection
steady slip
at depth
“thrust fault” in an elastic half-space, dipping 45 degrees
interseismic surface
deformation is given by the locked
portions of the mega-thrust sliding as a normal fault at the plate rate (Savage, 1983)
a more realistic geometry
vert
ical
h
ori
zon
tal
back-slip model
10D
D/2
Dlockedsection
steady slip
at depth
“thrust fault” in an elastic half-space, dipping 45 degrees
does not include strains due to plate
bending, if incorporated, discrepancy
removed, total interseismic + coseismic =
subduction block motion…
a more realistic geometry
Ravi Kanda
vert
ical
h
ori
zon
tal
elastic slab model
“thrust fault” in an elastic half-space, dipping 45 degrees
10D
D/2
Dlockedsection
steady slip
at depth
in a spun-up model, total interseismic slip fills in the the areas above the co-seismic slip-profile
periodically impose this co-seismic slip
slip on the fault:
below the locked region
b>0 thrust slip
surface interseismic displacements:
xxxxxx
oo
surface interseismic displacements:
xxxxxx
ooo
surface interseismic displacements motivation:
2003 Tokachi-oki eq. (M8)
Baba et al., 2003
x
data from Sue Owen
slight curvaturetectonic?
surface interseismic displacements motivation:
2003 Tokachi-oki eq. (M8)
Baba et al., 2003
x
data from Sue Owen
determination of plate coupling:
Suwa et al., 2006
shown is back-slip rate vbs
invert GPS velocities for distributions of normal slip (vbs) on the mega-thrust
use back-slip model (Savage,
1983) to determine the “coupling coefficient”
• vbs = vT coupled (C=1)
• vbs = 0 uncoupled (C=0)
this assumes that the interseismic deformation is constant throughout the interseismic period
10D
D/2
Dlockedsection
steady slip
at depthinvert GPS velocities for distributions of normal slip (vbs) on the mega-thrust
use back-slip model (Savage,
1983) to determine the “coupling coefficient”
• vbs = vT coupled (C=1)
• vbs = 0 uncoupled (C=0)
slip is not constant through the cycle
determination of plate coupling:
this assumes that the interseismic deformation is constant throughout the interseismic period
variation of coupling through an interseismic period
xxxxxx
xxx
variation of coupling through an interseismic period
xxxxxx
variation of coupling through an interseismic period
xxxxxx
Lapusta et al., 2000
this model only contains co-seismic slip in the locked regions, no interseismic slip-allowed in the locked regions…
contrary to dynamic calculations…
two (of the many) remaining issues:
still learning to drive…
“lockedness” – we assume full slip in locked patches (asperities)
some directions currently aiming for:
include heterogeneous elastic structure by computing K(z;) from FE models…
include other bulk rheologies – K(z;): “simple” semi-analytic models & quite complicated FE models…
model the GPS data of inter- & post-seismic observations in Hokkaido (2D, 3D planar, respecting slab geometry, & …)
gOcad
1968
19732003
slip models from Yamanaka and Kikuchi (2002) vertically exaggerated