EGU2020-19456
https://doi.org/10.5194/egusphere-egu2020-19456
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Poro-visco-elasto-plastic seismo-hydro-thermomechanical geodynamic models for subduction zones and induced seismicity

Taras Gerya1, Claudio Petrini, and Viktoriya Yarushina2
Taras Gerya et al.
  • 1ETH-Zurich, Institute of Geophysics, Department of Earth Sciences, Zurich, Switzerland (taras.gerya@erdw.ethz.ch)
  • 2Institute for Energy Technology, NO-2007 Kjeller, Norway

Natural and induced seismicity is widely investigated, and extensive knowledge has been acquired in the last years, but exact earthquake mechanisms remain elusive and poorly understood. The high impact of earthquakes on human society emphasizes that a deeper understanding of earthquake processes must be a priority in order to improve seismic hazard assessment and mitigate associated risks. Pervasive fluid flow is a key process significantly influencing rock physics and mechanics, and thus has a crucial impact on natural and induced earthquakes. Seismo-hydro-thermo-mechanical (SHTM) modelling is an important nascent branch of geodynamic modelling, which investigates evolution of coupled fluid-solid systems under conditions of both slow tectonic and fast seismic deformation rates. Here, we present a new fully coupled two-dimensional seismo-hydro-mechanical numerical code, with a poro-visco-elasto-plastic rheology, based on fully staggered finite differences with marker-in-cell technique, adaptive time stepping and global Picard iterations. The presented numerical code combines inertial mechanical deformation with pervasive fluid flow. The adaptive time stepping allows the resolution of co-seismic and interseismic phases with time steps ranging from milliseconds to years.

First, we demonstrate how fluid-bearing subducting rocks are intrinsically seismic and how seismic events in the form of highly localized ruptures spontaneously nucleate along the subduction interface. Nucleation and propagation of such events are driven by rapid fluid pressurization caused by visco-plastic compaction, counterbalanced by a nearly simultaneous and equivalent poroelastic decompaction inside the propagating and rupturing fault. Successive post and interseismic fluid pressure release, generated by poroelastic compaction along the fault, allows strength recovery of the megathrust. The model reproduces the broad range of seismic events present at the subduction interface, including slower events, regular earthquakes, and earthquakes that rupture the entire megathrust and reach velocities on the order of m/s, without employing slip rate dependent frictional properties.

Next, we show how our approach can be successfully adapted for fluid injection setups to model induced seismicity phenomena. The numerical code successfully modelled fluid induced seismic events and the resulting seismic wave propagation.  Preliminary results show that faults can form spontaneously and grow aseismically at the injection site thereby creating favorable conditions for the development of broad induced seismicity region where different faults can be activated seismically at different time.

Finally, we outline in short future SHTM modeling directions that should account for fracture-induced dilatation and dynamic permeability variations, thermal effects and three-dimensionality.

How to cite: Gerya, T., Petrini, C., and Yarushina, V.: Poro-visco-elasto-plastic seismo-hydro-thermomechanical geodynamic models for subduction zones and induced seismicity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19456, https://doi.org/10.5194/egusphere-egu2020-19456, 2020

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  • CC1: Comment on EGU2020-19456, Angela Maria Gomez Garcia, 07 May 2020

    Dear Dr. Gerya,

    Thank you very much for your excellent presentation.

    I would like to ask about your point of view regarding the possibility of having earthquakes in the continental mantle wedge of a subduction system. It seems that there is not a general agreement in the community regarding these events. However, I am studying the Nazca flab-slab in Colombia, using 3D lithospheric-scale data-integravite models, and what I observe is that there are some events possibly located within this wedge. 

    I have been interpreting them as possibly related with fluids migration, that is why I wanted to bring this topic to you.

    On the other hand, I am also interested in obtaining the temperature distribution at which earthquakes nucleate in this region. I was wondering if you are planning to publish your code? Right now I have results from steady-state simulations (https://meetingorganizer.copernicus.org/EGU2020/EGU2020-16409.html).

    Thank you very much for your time and feedback.

    Best regards,

    Ángela.

    • AC1: Reply to CC1, Taras Gerya, 07 May 2020

      Dear Angela,

      Thank you for your comment! The paper is currently in review. It is unlikely that the SHM code will be provided for free access since our other students still use it for their projects. However, seismo-thermo-mechanical codes are provided for free access on my textbook web-page: https://www.cambridge.org/us/academic/subjects/earth-and-environmental-science/structural-geology-tectonics-and-geodynamics/introduction-numerical-geodynamic-modelling-2nd-edition?format=HB&isbn=9781107143142

      Go to Resources  (see codes for Chapter 15).

      Recent work on fluid flow and faulting in the overriding plate:

      https://www.nature.com/articles/s41598-019-46191-y

      All the best.

      Taras

      • CC2: Reply to AC1, Angela Maria Gomez Garcia, 07 May 2020

        Thank you so much for your great feedback, Prof. Gerya.

        Kind regards,

        Ángela.