If you give two bits about quantitative seismic interpretation, amplitude maps, inversion, or AVO, then you need to know a bit about bits.

When seismic data is recorded, four bytes are used to store the amplitude values. A byte contains 8 bits, so four of them means 32 bits for every seismic sample, or a bit-depth of 32. As Evan explained recently, amplitude values themselves don’t mean much. But we want to use 32 bits because, at least at the field recording stage, when a day might cost hundreds of thousands of dollars, we want to capture every nuance of the seismic wavefield, including noise, multiples, reverberations, and hopefully even some signal. We have time during processing to sort it all out.

First, it’s important to understand that I am not talking about spatial or vertical resolution, what we might think of as detail. That’s a separate problem which we can understand by considering a pixelated image. It has poor resolution: it is spatially under-sampled. Here is the same image at two different resolutions. The one on the left is 300 × 240 pixels; on the right, 80 × 64 pixels (but reproduced at the same size as the other picture, so the pixels are larger).

But now consider an image with plenty of detail but no precision. On the left is an 8-bit image with 300 × 240 pixels (just like the left-hand image above, but without the colour). On the right is the same image at the same resolution, 300 × 240 pixels, but with only two bits per sample instead of eight.