Post on 21-Jan-2016
Geodetic Deformation, Seismicity and Fault Friction
Ge277- 2007
Sensitivity of seismicity to stress perturbations, implications for
earthquakes nucleation
Key Observation :
Seismicity rate and Geodetic strain rate are generally proportional, and both decays as t-1 following an earthquake
• Aftershocks and postseismic relaxation following the : – Mw7.6, Chichi earthquake (1999) – Mw 7.2 Landers Earthquake (1992)– Mw 8.1, Peru earthquake (2001)– Mw 8.7, Nias earthquake (2005)
• Background seismicity in the Nepal Himalaya
(Svarc and Savage, 1997)
CPA analysis show that all GPS stations follow about
the same time evolution f(t)
Postseismic Displacements following the Mw 7.2 1992 Landers Earthquake
Comparing aftershocks and afterslip following Landers EQ
(Perfettini and Avouac, 2004a)
Seismicity and Postseismic displacements follow the same relaxation curve consistent with the Omori Law.
Velocities relative to India(Bettinelli et al, 2006)
Geodetic deformation across the Nepal Himalaya
Creeping Zone17-18mm/yr
Locked Fault Zone,width 110km
Seismicity and Coulomb stress change due to interseismic stress accumulation
(Bollinger et al, JGR, 2004)
Seismicity coincides with the area where Coulomb stress increases by 4-6 kpa/a
Conceptual Model
Seismicity and Coulomb stress change due to interseismic stress accumulation
(Bollinger et al, JGR, 2004)
Seismicity coincides with the area where Coulomb stress increases by 4-6 kpa/a
Winter seismicity rate is twice as large as summer seismicity rate
Detrend GPS time-seriesSeasonal variation of Horizontal Displacements
Water level in Ganges Basin determinedfrom TOPEX-POSEIDON and GRACE
GUMBA-SIMRA
TOPEX-POSEIDON GRACE
Displacements induced by surface water level variations in the Ganges basin
Summer
Winter
Finite Element Modeling
Seasonal variations of seismicity and water level in the Ganges Basin
Seasonal variations of seismicity and water level in the Ganges Basin
Compression CompressionExtension
Strain induced by surface water level variations in the Ganges basin
Summer: Extension
Winter: Compression
Seasonal Coulomb stress variations
Coulomb stress variations are estimated to about 500 pa(<earth tides, 2-3kPa for T=12h and 14 days)
Coulomb stress rate
• Seasonal variations of geodetic displacements reflect deformation due to water level variations in the Ganges basin
• Interseismic Coulomb stress increase by 4-5 kPa/yr is modulated by seasonal variations of 500pa (corresponding to stress rate variation of 2-3kPa/yr) modulating the seismicity rate by a factor of 2.
Seasonal variation of Coulomb stress rate
6 kPa/yr
8 kPa/yr
With secular term added 10 kPa/yr
In these examples:– Seismicity rate and stress rate are
approximately proportional– The characteristic time associated with the
stress variations is of the order of 1 yr.
Standard Coulomb failure
- seismicity rate obeys :0
0 S
SRR
- so, for periodic loading :
nS
00
minmax
0
minmax 2STS
SS
R
RR m
Assuming , 0S
0S
0S
(Lockner and Beeler, 1999; Heki, 2003)
Standard Coulomb failure
For periodic loading : 00
minmax
0
minmax 2STS
SS
R
RR m
Seismicity rate should be much more sensitive to earth tides.
This is not observed, probably because rupture is a time-dependent process, as suggested by rock mechanics experiments.