Friday, November 11, 2016

Cushing OK Earthquake

On 7 Nov 2016 there was a magnitude 5.0 earthquake (EQ) at 5 km depth about 2 km W of Cushing, Oklahoma. The earthquake was felt by many in my town of Fayetteville, Arkansas. Although I did not feel the EQ myself, I was interviewed by three local television stations to provide some insight. The interviews went well and appeared on Nov 8.

This got me thinking about simulating the EQ. A few months ago I set out to learn a bit about the python computer language. In the process I found some remarkable open source codes. The one on point here is fatiando a terra written in 2012 by (then) PhD student Leonardo Uieda. Leo is a research department all on his own.

Anyway, one thing fatiando does is elastic seismic modeling and there is a demo script (seismic_wavefd_elastic_psv.py) in the cookbook. This generates a neat simulation of elastic waves in a crust/moho model and the (x,z) seismic reading from one seismometer. It is a movie, but here is the last frame.

Fig 1. Default simulation result from fatiando script seismic_wavefd_elastic_psv.py 

You can see all the elements are here to simulate the Cushing EQ, we just need to change a few things. Specifically:
     (1) Crust (granite) properties can be localized using a deep well in Osage County, OK that drilled almost 2 km of granite. The params are vp = 5970 m/s, vs = 3500 m/s and density 2650 kg/m^3.
     (2)  Crust thickness in N Oklahoma and Arkansas is about 45 km thick (reference, figure 7).
     (3) The seismometer should at Fayetteville, 240 km from the EQ.
     (4) Since all the action in Fayetteville is over by 85 seconds, limit the simulation to 100 sec.

With these edits and running the python script now gives the Cushing EQ as felt in Fayetteville AR case. Very cool. Thank you Leo.

Fig 2. Simulation result for 7 Nov 2016 Cushing EQ as felt at Fayetteville AR. 


1 comment:

Leonardo Uieda said...

Hi Chris,

I'm really glad you liked the project and could do something useful with it!

The elastic wave modeling module is something I coded up for a class and never really took the time to properly test it, so be aware that the results might not be accurate. I wouldn't recommend it for research but it's fine for illustrating wave propagation in classes (that's what I use it for).

I've been working a new implementation that integrates with the Jupyter notebook for some time (https://github.com/fatiando/fatiando/pull/308) but I haven't been able to finish it yet. I'd love your feedback on the interface. Here is an example from my seismics class (it's in Portuguese but you can get the idea by running the code): http://mybinder.org/repo/leouieda/geofisica2/notebooks/notebooks/1-ondas-sismicas.ipynb

That link should open an executable notebook running on mybinder.org but it's been down a lot lately. Try again later if it doesn't open. You can find the other notebooks from the class at https://github.com/leouieda/geofisica2#cronograma (use the "executar" links).

It took me such a long time to see this post. I only noticed because of the Google Analytics traffic. Turns out I hadn't updated my RSS feed to include your blog when moving to Feedly. Subscribed now :)

Leo