Geodetic Deformation, Seismicity and Fault Friction Ge277- 2007 Sensitivity of seismicity to stress...
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Transcript of Geodetic Deformation, Seismicity and Fault Friction Ge277- 2007 Sensitivity of seismicity to stress...
![Page 1: Geodetic Deformation, Seismicity and Fault Friction Ge277- 2007 Sensitivity of seismicity to stress perturbations, implications for earthquakes nucleation.](https://reader035.fdocuments.us/reader035/viewer/2022062309/5697c02c1a28abf838cd912c/html5/thumbnails/1.jpg)
Geodetic Deformation, Seismicity and Fault Friction
Ge277- 2007
Sensitivity of seismicity to stress perturbations, implications for
earthquakes nucleation
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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
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(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
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Comparing aftershocks and afterslip following Landers EQ
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(Perfettini and Avouac, 2004a)
Seismicity and Postseismic displacements follow the same relaxation curve consistent with the Omori Law.
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Velocities relative to India(Bettinelli et al, 2006)
Geodetic deformation across the Nepal Himalaya
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Creeping Zone17-18mm/yr
Locked Fault Zone,width 110km
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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
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Conceptual Model
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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
![Page 11: Geodetic Deformation, Seismicity and Fault Friction Ge277- 2007 Sensitivity of seismicity to stress perturbations, implications for earthquakes nucleation.](https://reader035.fdocuments.us/reader035/viewer/2022062309/5697c02c1a28abf838cd912c/html5/thumbnails/11.jpg)
Winter seismicity rate is twice as large as summer seismicity rate
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Detrend GPS time-seriesSeasonal variation of Horizontal Displacements
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Water level in Ganges Basin determinedfrom TOPEX-POSEIDON and GRACE
GUMBA-SIMRA
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TOPEX-POSEIDON GRACE
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Displacements induced by surface water level variations in the Ganges basin
Summer
Winter
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Finite Element Modeling
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Seasonal variations of seismicity and water level in the Ganges Basin
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Seasonal variations of seismicity and water level in the Ganges Basin
Compression CompressionExtension
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Strain induced by surface water level variations in the Ganges basin
Summer: Extension
Winter: Compression
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Seasonal Coulomb stress variations
Coulomb stress variations are estimated to about 500 pa(<earth tides, 2-3kPa for T=12h and 14 days)
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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
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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.
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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
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0S
0S
(Lockner and Beeler, 1999; Heki, 2003)
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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.