[CIG-SEISMO] [Specfem3D Cartesian]- Using a CMTSOLUTION source to trigger a critically-stressed fault

Tue Apr 10 07:08:31 PDT 2018

Thank you, Surendra!

I figured out how to deal with it after talking to Kangchen.

I put a Mw 6.2 Right-lateral EQ 1km away from a dynamic fault.

This scenario results in a dynamic stress changes of ~0.5MPa 

The results look reasonable to me.

Best,

Ge

From: Surendra Nadh Somala <surendra at iith.ac.in>
Date: Tuesday, April 10, 2018 at 3:01 AM
To: Ge Li <ge.li2 at mail.mcgill.ca>
Cc: Kangchen Bai <kbai at caltech.edu>, Dimitri Komatitsch <komatitsch at lma.cnrs-mrs.fr>, <cig-seismo at geodynamics.org>, <ampuero at geoazur.unice.fr>
Subject: Re: [CIG-SEISMO] [Specfem3D Cartesian]- Using a CMTSOLUTION source to trigger a critically-stressed fault

Dear Ge,

Currently, the implementation is such that all the fault in a particular simulation should be either Kinematic or Dynamic.

Nevertheless, you can run a kinematic simulation, observe the stress changes on the other fault and setup a dynamic rupture simulation based on the updated stresses.

Btw, what is the magnitude of the point source (CMTSOLUTION) you have put in your simulation?

Best,

Surendra

___________

Surendra Nadh Somala

Assistant Professor
Department of Civil Engineering (Block-E, 208)
Indian Institute of Technology (IIT) Hyderabad

Kandi, Sangareddy
Telangana, India - 502285

Phone : +91 (0)40 2301-8457 

http://civil.iith.ac.in/surendra/ 

On Tue, Apr 10, 2018 at 1:08 AM, Ge Li <ge.li2 at mail.mcgill.ca> wrote:

Hi Kangchen and Dimitri,

Thanks for your reply!

Kangchen, can you give me more explanations on ‘fault-node splitting’?

Do you mean the split-node technique used during the mesh process? I followed the 

instructions provided in the specfem3d manual to create a Cubit mesh file. The 

mesh works well for a ‘step-over’ scenario and I did observe the  dynamic stress transfer.

Back to the test mentioned in my previous email, where I put a point source 

(Mw~6 Right-lateral strike slip) about only 1km away from the fault surface. I also observed

stress changes, but with a magnitude of ~  0.0682Pa. Considering the initial stress level of 

82.1MPa, I suspected these stress changes are numerical?

Also is it possible to implement both dynamic and kinematic fault in a model, i.e. one fault is

Kinematic and the other one is dynamic.

Thanks !

Best regards,

Ge

From: Kangchen Bai <kbai at caltech.edu>
Date: Monday, April 9, 2018 at 1:12 PM
To: Dimitri Komatitsch <komatitsch at lma.cnrs-mrs.fr>
Cc: <cig-seismo at geodynamics.org>, Ge Li <ge.li2 at mail.mcgill.ca>, Surendra Nadh Somala <surendra at iith.ac.in>, <ampuero at geoazur.unice.fr>
Subject: Re: [CIG-SEISMO] [Specfem3D Cartesian]- Using a CMTSOLUTION source to trigger a critically-stressed fault

Hi Ge,

Triggering a dynamic rupture with a point source is do-able with the code. You should see dynamic stress changes as the wave goes across the fault.

 I actually did similar things before by mistake --- I forgot to turn off the point source when doing a dynamic rupture simulation and see the circular stress pattern on the fault. 

We also did the work of one fault rupture triggering another using the code (See Bai & Ampuero 2017 

https://doi.org/10.1002/2017JB014848 

 ), the stress transfer is not a problem as is shown in Fig 6 & 7.

If you do not see stress changes, there must be something wrong with the settings. 

I suspect the most plausible scenario is that the fault node is not split in which case the stress remain constant anyhow.

Let me know if you have more questions.

Best,

Kangchen

On Mon, Apr 9, 2018 at 7:21 AM, Dimitri Komatitsch <komatitsch at lma.cnrs-mrs.fr> wrote:

Dear Ge Li,

Thank you very much for your email and for your interest in the work of the community around the package.

Yes, if you want to mimic an extended source using a kinematic source model, you can use many CMTSOLUTION sources that are triggered at different times and at slightly different locations (see e.g. the discussion about extended sources around equation (A12) of http://komatitsch.free.fr/preprints/GJI_1999_figure16_error_fixed_equation3_typo_fixed.pdf, and the way we mimic a Hamming quasi-plane wave using 1000 such sources in http://komatitsch.free.fr/preprints/Ultrasonics_Moysan_2016.pdf figure 5).

If you want a dynamic rupture source model, i.e. something more sophisticated, the package can do that based on the great work of Jean-Paul Ampuero, Surendra Nadh Somala, Kangchen Bai and other people in the community, they can give you more details (they will know much more about this than I do :-)
Let me thus cc them.

Best regards,
Dimitri.

On 04/05/2018 03:00 AM, Ge Li wrote:

To Whom It May Concern:

I’m a PhD Candidate in geophysics at McGill University. Currently I’m using

Specfem3D Cartesian for my research.

I’m wondering is it possible to trigger an earthquake on a fault using a CMTSOLUTION source?

I tried several simulations by setting a critically stressed fault and a CMTSOLUTION point source.

The source (Mw~6 Right-lateral strike slip) was located about only 1km away from the fault surface.

But it turned out the stresses on the fault surface(dynamic slip-weakening) remain unchanged.

Based on these tests, I supposed that a CMTSOLUTION won’t change the stress level on a fault surface. Is it correct?

Or did I miss something here?

Thanks! I’m looking forward to your reply!

-- 

*Ge Li*

/Ph.D. Candidate/

/Department of Earth & Planetary Science, /

/McGill University/

/3450 University Street/

/Montreal, QC, Canada /

/H3A 0E8/

/ge.li2 at mail.mcgill.ca <mailto:ge.li2 at mail.mcgill.ca>/

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-- 
Dimitri Komatitsch, CNRS Research Director (DR CNRS)
Laboratory of Mechanics and Acoustics, Marseille, France
http://komatitsch.free.fr

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