Segall, P.

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Coupled Thermo-Poro-Mechanical 
Effects in Earthquakes and Slow 
Slip Events
Paul Segall
Stanford University
Allan Rubin (Princeton)
Takanori Matsuzawa (NIED, Tokyo), Stuart Schmitt (Stanford)
Episodic Tremor and Slip
Dragert et al, Science, 2001
Obara, Science, 2002
Rogers and Dragert, Science, 2003
Cascadia Slow Slip Events
Szeliga et al, in review
Figure Courtesy of Tim Melbourne Slip rate ~ 10 x plate-rate
Kilauea Silent Earthquakes
Cervelli et al, Nature, 2002; Segall et al, Nature 2006
Mechanics of Slow Slip?
•Change in frictional behavior at high slip speed [e.g., 
Shibazaki and Iio, 2003].
•Rate-state friction near neutral stability  [Liu and Rice, 
2007.
•Dilatant stabilization of slip [this study].
Under what circumstances might a deep slow slip 
event trigger a damaging megathrust earthquake? 
Dilatant Strengthening
Frictional sliding causes 
dilatancy
Fault zone pore pressure 
decreases if dilatancy rate 
exceeds rate of fluid influx
Increases effective normal 
stress inhibiting slip
[Rice 1975; Rice and Simons, 1976l Rudnicki, 1979; Martin, 1980]
Pore Fluid
Fault Plane
Dilatancy and Slow Slip
V∞V∞ Friction + Dilatancy2
xx
y
W
Effect of Dilatancy on Slip-rate
No Dilatancy Dilatancy
Two dimensional elasticity, rate-state friction with  dilatancy (Segall and 
Rice, 1995), and one dimensional membrane diffusion.
Slow Slip in Subduction Geometry
Scaling Parameters
Without Dilatant Strengthening, W/h* is limited
Courtesy Allan Rubin
Moment Rate
W / h* = 25 W / h* = 7
Critical crack dimension h* for nucleation (Ruina, 1983)
With Dilatancy W/h* appears to be 
essentially unbounded
QuickTime™ and a
 decompressor
are needed to see this picture.
Thermal Pressurization
Frictional sliding 
generates heat
Pore fluid expands more 
than rock
Pore pressure increases if 
rate of heat production 
exceeds rate of fluid and 
heat transport
Reduces effective normal 
stress 
Sibson (1973), Lachenbruch (1980); Mase and Smith (1985, 1987); Lee and 
Delaney (1987); J. Andrews (2002): Noda and Shimamoto (2005); Wibberly and 
Shimamoto (2005): Rempel and Rice (2006);  Rice (2006);  Bizzari and Cocco
(2006); Segall and Rice (2006)
Questions
1. At what point do shear heating effects dominate 
frictional weakening?
•“Since the thermal process is important only for 
large earthquakes …” Kanamori and Heaton, 2000•.Andrews [2002] also suggests thermal 
pressurization effects important at ~ M 3-4.
• How does thermal pressurization 
influence earthquake slip and slip 
rate?
• Will an increase in pore-pressure 
limit the temperature rise and 
inhibit melting?
Kanamori and Heaton, 2000
Shear Heating Induced 
Thermal Pressurization
Influence of Thermal Pressurization on 
Nucleation Dimension
Without Thermal Pressurization With Thermal Pressurization
Aging Law, a/b = 1/3;  Dieterich (1992), Rubin and Ampuero (2005)
Weakening Mechanisms
Change in μ(θ,v)(σ−p0) Change in μ0(σ − p)
10-4 m/s
Conclusions and 
Speculations
1.Dilatancy capable of stabilizing 
against rapid slip.
2.Slip rates and repeat times 
plausibly in the range of 
observed slow-slip events.
3.In the absence of dilatancy
thermal pressurization becomes 
important well before seismic 
slip-rates.
4.Slow vs. fast slip may be 
controlled by competition between 
dilatant strengthening and 
Full Diffusion Normal to Fault
Analytical Approximation
Lockner, Naka, Tanaka, Ito and Ikeda, 
“Permeability and strength of core 
samples from the Nojima fault of the 
1995 Kobe earthquake”, USGS Open 
File Rpt. 00-129, 2000
Possible Active
Strands
10 -9
10 -8
10 -7
10 -6
10 -5
10 -4
P
e
r
m
e
a
b
i
l
i
t
y
,
 
D
a
r
c
y
NIED Borehole
Shallow Zone
(b)
10 -9
10 -8
10 -7
10 -6
10 -5
10 -4
P
e
r
m
e
a
b
i
l
i
t
y
 
(
d
a
r
c
y
)
Intact Rock
Permeability
Damage
Zone
Shear
Zone
GSJ Borehole
MATRIX PERMEABILITY
(a)
10 -9
10 -8
10 -7
10 -6
10 -5
10 -4
P
e
r
m
e
a
b
i
l
i
t
y
NIED Borehole
Intermediate Shear
Zone
(c)
Horizontal Distance from Shear Zone, m
-30 -20 -10 0 10 20 30
10–19 m2
10–17 m2
10–19 m2
10–17 m2
10–19 m2
10–17 m2
General Case with Rate-State Friction
 Thermal pressurization causes large displacement, slip 
velocity, and low frictional stress
These are spring slider models
Thermal Pressurization limits 
temperature and inhibits 
melting
Slow Slip Events World Wide
•Cascadia [Dragert et al, 2001; Miller et al, 2002, Szeliga et al, 2004]. 
•Southwest Japan [Hirose et al, 1999; Miyazaki et al, 2006; Ozawa et al, 20002]
•Mexico [Kostoglodov et al, 2003, Lowry et al, 2005.]
•New Zealand [Douglas, 2005,] 
•Kilauea volcano [Cervelli et al 2002, Segall et al, 2006,Brooks et al, 2006]. 
Boso, Japan, 
Ozawa (2003).
S.W. Japan, Obara, 2004
Seismicity Triggered by Slow Slip
Segall et al, Nature, 2006
Kilauea Silent Earthquake
Cervelli et al, Nature, 2002
8km Deep Fault Fits GPS Data
Relocated Earthquakes
Segall et al,  Nature, 2006
Analytical Approximation
Shear Heating Induced 
Thermal Pressurization
Cumulative 
number of 
earthquakes
Fault slip
Earthquakes Lag Slip
Segall et al,
Nature, 2006
2005 Slow 
Slip Event

Dilatancy Constitutive Law (Segall and Rice, 
1995), based on Marone lab data
Test of Finite Difference: Const 
μ and v
Analytical Result, 
Rice (2006)


Coupled thermo-poro-mechanical effects in earthquakes and slow slip events

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Coupled thermo-poro-mechanical effects in earthquakes and slow slip events

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