geodetic deformation, seismicity and fault friction ge277- 2007 sensitivity of seismicity to stress...

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  • Geodetic Deformation, Seismicity and Fault FrictionGe277- 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

  • 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

  • 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 GRACEGUMBA-SIMRA

  • TOPEX-POSEIDON GRACE

  • Displacements induced by surface water level variations in the Ganges basinSummerWinter

  • Finite Element Modeling

  • Seasonal variations of seismicity and water level in the Ganges Basin

  • Seasonal variations of seismicity and water level in the Ganges BasinCompressionCompressionExtension

  • Strain induced by surface water level variations in the Ganges basinSummer: ExtensionWinter: Compression

  • Seasonal Coulomb stress variationsCoulomb stress variations are estimated to about 500 pa(
  • Coulomb stress rateSeasonal variations of geodetic displacements reflect deformation due to water level variations in the Ganges basinInterseismic 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 rate6 kPa/yr 8 kPa/yrWith secular term added 10 kPa/yr

  • In these examples:Seismicity rate and stress rate are approximately proportionalThe characteristic time associated with the stress variations is of the order of 1 yr.

  • Standard Coulomb failure- seismicity rate obeys :- so, for periodic loading : Assuming ,

  • (Lockner and Beeler, 1999; Heki, 2003)

  • Standard Coulomb failureFor periodic loading : 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.

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