Stress, earthquakes, volcanoes
Tim Wright, University of Leeds
Questions
• Fundamental physics governing
earthquake faults, magma emplacement?
• How do earthquakes and volcanoes
interact?
• Can we improve forecasting of
earthquakes or eruptions?
Selected examples
1. Earthquake induced triggered slip
(Shahdad thrust, Iran)
2. Tectonic control of volcanic intrusions
(Afar, Ethiopia)
3. Volcanic control of earthquake
mechanisms (Montserrat)
4. Coulomb stress and earthquake
forecasting (various)
Coseismic triggered slip on the
Shahdad Thrust, Eastern Iran
Fielding, E.J., T.J. Wright, J. Muller, B.E. Parsons, and R. Walker, Geology, 32(7), 577-580, 2004
Triggered Slip on the Shahdad Thrust, Eastern Iran
Iran
S
Dasht-e-Lut
Sh
X’
ah
da
d
Th
ru
st
F
X
Gowk Fault
Fielding, E.J., T.J. Wright, J. Muller, B.E. Parsons, and R. Walker, Geology, 32(7), 577-580, 2004
SAR Interferogram for the Mw 6.6 Fandoqa
Earthquake, 14 March 1998, Eastern Iran
Fielding, E.J., T.J. Wright, J. Muller, B.E. Parsons, and R. Walker, Geology, 32(7), 577-580, 2004
Fielding, E.J., T.J. Wright, J. Muller, B.E. Parsons, and R. Walker, Geology, 32(7), 577-580, 2004
Shear stress
increases by
0.02MPa
Fielding, E.J., T.J. Wright, J. Muller, B.E. Parsons, and R. Walker, Geology, 32(7), 577-580, 2004
Fielding, E.J., T.J. Wright, J. Muller, B.E. Parsons, and R. Walker, Geology, 32(7), 577-580, 2004
Observed range change
Predicted range change
 Thrust surface is a low friction surface, or at threshold for failure.
Fielding, E.J., T.J. Wright, J. Muller, B.E. Parsons, and R. Walker, Geology, 32(7), 577-580, 2004
Tectonic stress controlling dyke
injections at the Dabbahu Rift, Afar
(Ethiopia)
I.J.Hamling, Ayele, A., Calais, E., Ebinger, C., Keir, D., Lewi, E., Wright, T.J., Yirgu, G., Geophys. J. Int., in prep
A major rifting episode began in September 2005 in the Afar
depression, a young, subaerial seafloor spreading centre on
the Nubia-Arabia plate boundary
The Afar Triple Junction
Arabia
Nubia
(Africa)
Semara
Sept 05
Somalia
A major rifting episode began in September 2005 in the Afar
depression, a young, subaerial seafloor spreading centre on
the Nubia-Arabia plate boundary
Faults and Fissures – similar to
structures seen on mid-ocean ridges
The Afar Triple Junction
Arabia
Nubia
(Africa)
Semara
Sept 05
Somalia
Liz Baker, March 2006
A major rifting episode began in September 2005 in the Afar
depression, a young, subaerial seafloor spreading centre on
the Nubia-Arabia plate boundary
Liz Baker, March 2006
Anthony Philpotts, October 2005
Liz Baker, March 2006
James Hammond, Jan 2006
6 May – 28 Oct 2005
Wright et al., Nature 2006
• 2.5 km3 magma intruded along dyke (Mt St Helens 1980 1.2 km3;
Krafla ~ 1 km3 total).
• ~0.5 km3 sourced from Dabbahu and Gabho volcanoes at North.
• This was the first (and largest) in an ongoing sequence of dyke
injections.
June 2006
June 2006
September 2005
June 2006
July 2006
September 2006
December 2006
January 2007
August 2007
November 2007
Stress drop
~ s(E/H)
~ 10-20 MPa
Buck et al., JGR 2006
• Location, length and width of intruded
dykes controlled by Magma pressure and
Tectonic Stress
• Eruptions occur when tectonic stress
relieved
Buck et al., JGR 2006
Volcanic stresses modifying tectonic
stress field
3 March 2004
http://www.mvo.ms
T,

3
1
,
P

,
P
1
T,

3
Normal seismicity, P-axis aligned
with regional stress
Reversed focal mechanisms
observed preceding eruptions or
changes in style of eruption
Roman et al., EPSL 2006, Geology 2006, JVGR 2008
Regional 1
Dyke aligned
parallel to 1
Roman et al., EPSL 2006, Geology 2006, JVGR 2008
Earthquake-induced stress changes
Animations courtesy Ross Stein, USGS (http://quake.wr.usgs.gov/~ross)
Animations courtesy Ross Stein, USGS (http://quake.wr.usgs.gov/~ross)
Coulomb Failure Stress
i.e. CFS = shear stress + effective coefficient of friction * normal stress
Animations courtesy Ross Stein, USGS (http://quake.wr.usgs.gov/~ross)
M6.5 Big Bear earthquake
occurs 3 hours 26 minutes
after M7.4 Landers
mainshock
King et al., 1994
1994 Northridge Earthquake (M6.7)
Stein et al, 1999
=
Seismicity Rate Equation (Dieterich, 1994)
1995 Kobe Earthquake (M6.9)
Earthquake Probability Forecasting:
The 2008 Sichuan earthquake
Submitted manuscript by Toda et al.
Early results available on web
Questions
• Fundamental physics governing
earthquake faults, magma emplacement?
• How do earthquakes and volcanoes
interact?
• Can we improve forecasting of
earthquakes or eruptions?