Comments seismic

OMG... this is my first pull request.
And I gave up on the equation for attenuation correction in the docs, I couldn't get that to work.
Also, I made some unimplemented functions private, so they wouldn't show up in the doc, but there might be a better way of doing that.
please add something like "returns a sorted list of depths where this seismic data is specified at. This allows you to compare the seismic data without interpolation.".