I hadn't heard that PDEs were crucial to the practical progress in fracking. The applied math I heard about was really mostly just the fast Fourier transform (

I hadn't heard that PDEs were crucial to the practical progress in fracking. The applied math I heard about was really mostly just the fast Fourier transform (FFT) for deconvolution of seismic signals to identify rock layers. The FFT was in, what, 1968 or so so 40+ years ago? Well, the computers of 1968 could do some really good FFT calculations.