Adding normal and reverse faults to an impedance model with Python

This is a short and sweet follow-up to yesterday’s post Making many synthetic seismic models in Python, in which I want to show how to add oblique faults to an impedance model, as opposed to a vertical one.

In the pseudo-code below, with the first line of code I select one of the impedance models from the many I created, then in lines 2 and 3, respectively, make two new versions, one shifted up 5 samples, one shifted down 5 samples. The impedance values for the extra volume added – at the bottom in the first case, the top in the second – are derived from the unshifted impedance model.

Next, I make two copies of the original, call them normal and reverse, and then replace the upper triangle with the upper triangle of the shifted down and shifted up versions, respectively.

unshifted = impedances[n]
up = sp.ndimage.interpolation.shift(unshifted, (5,0), cval=unshifted[0,0] * 0.9)
down = sp.ndimage.interpolation.shift(unshifted, (-5,0), cval=unshifted[0,-1] * 0.8)
normal = copy.deepcopy(unshifted)
reverse = copy.deepcopy(unshifted)
sz = len(unshifted)-1
normal[np.triu_indices(sz)] = up[np.triu_indices(sz)]
reverse[np.triu_indices(sz)] = down[np.triu_indices(sz)]

Done!
The results are shown in the figure below.

Left: unfaulted impedance model; center, model with normal fault; right, model with reverse fault.

2 responses to “Adding normal and reverse faults to an impedance model with Python

  1. (np.triu_indicies)[https://docs.scipy.org/doc/numpy-1.10.4/reference/generated/numpy.triu_indices.html], I learned something new?

    Next, how about using np.argwhere() to return the indicies above or below a curved listric fault, or antithetic fault…I can almost see it now!

    • I like the idea of np.argwhere() Evan… I was also thinking of thrust faults with ramp-flat-ramp geometry, all these are very doable. Perhaps, though, as Matt has commented on the SU slack channel, probably at some point might as well be working in pynoddy….

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