# Seismic travel time simulation for 1D layered velocity distribution

**URL:** <https://simpeg.discourse.group/t/seismic-travel-time-simulation-for-1d-layered-velocity-distribution/124>\
**Category:** Getting Started\
**Created:** [June 25, 2020, 12:26am UTC](https://simpeg.discourse.group/t/seismic-travel-time-simulation-for-1d-layered-velocity-distribution/124 "2020-06-25T00:26:24Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Astor](https://yyz2.discourse-cdn.com/free1/user_avatar/simpeg.discourse.group/astor/32/189_2.png) [@Astor](https://simpeg.discourse.group/u/Astor)\
**Post date:** [June 25, 2020, 12:26am UTC](https://simpeg.discourse.group/t/seismic-travel-time-simulation-for-1d-layered-velocity-distribution/124/1 "2020-06-25T00:26:24Z")

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Hi,

I’m new to simpeg and I’m looking for a simplified forward simulation of seismic travel time based on 1D layered velocity/slowness. Can the 2D version be degraded to solve such a 1D problem?

Thanks! Looking forward to your response.

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**Author:** ![sgkang09](https://yyz2.discourse-cdn.com/free1/user_avatar/simpeg.discourse.group/sgkang09/32/8_2.png) [@sgkang09](https://simpeg.discourse.group/u/sgkang09)\
**Post date:** [July 9, 2020, 3:52pm UTC](https://simpeg.discourse.group/t/seismic-travel-time-simulation-for-1d-layered-velocity-distribution/124/2 "2020-07-09T15:52:15Z")

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Hi Aster,

Sorry for being late reply.  
SimPEG has a simple travel time tomography code, but it does not take account refraction (and reflection) of the seismic ray.

So, I am not sure this is a relevant code that can serve your purpose. If you can clarify what you are trying to do, I could better answer.

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<div class="post-metadata">

**Author:** ![Astor](https://yyz2.discourse-cdn.com/free1/user_avatar/simpeg.discourse.group/astor/32/189_2.png) [@Astor](https://simpeg.discourse.group/u/Astor)\
**Post date:** [August 2, 2020, 5:17am UTC](https://simpeg.discourse.group/t/seismic-travel-time-simulation-for-1d-layered-velocity-distribution/124/4 "2020-08-02T05:17:25Z")

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Hi Seogi,

Thank you for your reply. I am also new to seismic data processing and may have some misunderstanding of the travel time tomography. In my opinion, there are two categories, reflection tomography and transmission tomography. And I think the implementation on SimPEG belongs to the latter, suitable for the borehole-to-borehole case or surface-to-borehole case. You said the implementation on SimPEG does not take account refraction either. Does it mean that it only considers the straight rays?  
I’d like to find a forward and inverse code to achieve accuracy travel time tomography. And there may still be misunderstandings, so please don’t hesitate to point out any possible mistakes. Thanks.