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Research interests - Einat Aharonov | Institute of Earth Sciences

Research interests - Einat Aharonov

Dry granular deformation

 
Geolgical faults are usually filled with a layer of granular rock fragments, termed “fault gouge”, controlling shear behavior. Understanding such gouge zones help us understand earthquakes and landslides.
 
  •  At a critical porosity a "phase transition" occurs between Solid (jammed) and Fluid like (flowing) modes of deformation of granular media  (Aharonov and Sparks, PRE, 1999).  Under constant applied stress, deforming granular layers naturally evolve to this critical state. Our result explains the 'critical void ratio' observed in soil mechanics as a rigidity phase transition.
 
  •  Shear-strain distribution within shearing granular layers (Aharonov and Sparks, PRE, 2002): Applying different boundary conditions moves granular shear mode from fluid (F)-like to solid (S)-like and the shear profiles change accordingly.

 

  • A ‘Stick-slip’ instability naturally arises in granular media sheared by elastic forcing  (Aharonov and Sparks, JGR, 2004). The stick-slip deformation  is similar to earthquakes and the quiescent periods in between.  

                         

The large-scale complex behavior of the layer is dictated by the statistical distribution of forces transmitted across grain contacts. Prior to large slip - i.e. prior to an earthquake in our granular layer-  accelertaing motion occurs on contacts carrying weak forces. Slip occurs when the support of the stress chains is reduced. Our model show precursers to earthquakes.

                                

 

Coupled fluid - granular deformation

Although dry deformation of faults and landslides exhibits rich behavior, fluids usually fill pores between grains, playing a crucial role in controlling  stability and shear. The pressure of pore-fluids in fault zones is a major parameter controlling earthquakes and landslides, but its evolution during sliding is not well understood. We have added pore-fluids to our codes, allowing us to look at coupled effects of pore-pressure evolution with granular deformation (Goren et al 2010, Goren et al 2011), and gain basic new insights regarding mechanisms of pore-pressure induced liquefaction (liquefaction is a major cause for infrastructure damage during earthquakes) and regarding fluid effects on shear in GM (Aharonov et al 2013; Goren et al 2013).

Landslides

Landslides constitute a major worldwide natural hazard. In addition, landslides and catastrophic slope failures often control long-term slope erosion rates and geomorphological evolution. The need to understand landslide frequencies, initiation and travel modes is becoming increasingly evident, yet the most basic questions are still open. We performed (Katz and Aharonov, EPSL 2006) analog experiments  to explain why the distribution of natural landslide sizes is similar world-wide. The experiments found that distribution of heterogeneity may be a major control on the size distribution of natural landslide inventories.

In Klar et al 2011 we used basic mechanical modeling to explore a related question: why the geometry of slides is found to be self-similar worldwide

 


Following these findings we are now inlvolved in a large collaborative effort for the study of underwater slides along the Israeli coast: we are mapping the underwater slides, and studying how earthquake triggering, soil parameters, salt tectonics, and seeping fluids affect the Israeli shelf stability, slide distribution, and observed slide morphology. This study has practical implications for infrastructure development for the new Oil and Gas industry. 

Compaction bands

Compaction bands are naturally occurring discrete zones of deformation, associated with mechanical compaction of initially high porosity rocks. Compaction features play an important role in the distribution of permeability and stress in sedimentary basins. In Katsman et al, Mech of Materials, 2005  we  present a spring-network computer model (SNM) and use it to study the formation of compaction bands, the  model predicts and explains the physics of compaction bands .

 

 

The reason why defects like cracks and notches control compaction bands was shown and explained by Katsman et al, JSG, 2006

Pressure solution

Pressure solution is a process by which solid rock mass is dissolved at zones of high stress, moved through the pore fluid, and precipitated at zones of lower stress. Despite the fact that pressure solution is responsible for "chemical compaction" and is believed to be a very  important ductile mechanism operating in the Earth's upper crust, it remains poorly understood. We are currently studying pressure solution both theoretically and experimentally. New and exciting experiments (performed by previous PhD students, Dr Z Karcz, and Dr L Laronne, in calloboration with Prof C Scholz from Lamont, and Drs D Ertaz and R Pollizotti from ExxonMobil) on the kinetics of pressure solution in Halite, show that pressure solution is a dynamic process  which also interacts closely with plasticity (Karcz et al, Geology 2006, JGR 2008). In addition we find that damage controls pressure solution at least as much as stress (Laronne et al 2014, in prep)

Stylolites 

In many sedimentary rocks pressure solution naturally localizes into large-scale dissolution surfaces, termed stylolites. Although stylolites play a crucial rule in permeability of hydrocarbon reservoirs, they have not yet been successfully produced in the lab at a large scale (and not for lack of trying), and the mechanics of their formation is not well understood.

Our SNM model may help to unravel the process. It suggests that clay enhancement of pressure solution plays a crucial role in creating styolites (Aharonov & Katsman American J of Science, 2009)

The SNM model results and a complementary theory demonstrated that both localized mechanical and chemical compaction progresses as an edge-dislocation, and not as anti-cracks as previously suggested (Katsman and Aharonov GRL 2006; Aharonov & Katsman American J of Science, 2009)

Recently we have been complementing our  modeling by field-work on stylolite networks.

We observe more than km long styolites (Laronne et al 2012), the roughness of which allows us to understand their history and assess the amount of dissolution on them.

In addition, we observed and define different catagories of stylolite networks which both help us understand their 3D connectivity and suggest the way they evolve  is connected to both the stress distribution and to initial clay distribution during sedimentation (Laronne et al 2014).

 

data and computer programs

 

 Matlab subroutine (calculates how friction varies with slip rate at various T and normal stress)

that was used to run the model as described in Aharonov, E., & Scholz, C. H. (2018). A Physics‐Based Rock Friction Constitutive Law: Steady State Friction. Journal of Geophysical 

Research: Solid Earth123(2), 1591-1614


 Matlab subroutine (calculates how friction varies with depth in the crust and where it cuts the power low creep regime of Hirth et al 2001)

 used to run the model as described in Aharonov, E., & Scholz, C. H. (2019).The Brittle-Ductile Transition Predicted by a Physics-based Friction Law/ Journal of Geophysical 

Research: Solid Earthin press. 

 

 

היבטים טכנולוגיים וסביבתים של אסדת לוויתן ואסדת תמר

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