Russell,

"Can a 3.0 be mathematically porportional to middle C and a 3.8 mathematically porportional to E#?"

I think the larger the magnitude the larger the volume throughout the full range (of .033 to 10 Hz), with more increase in the bass.

To make it audible, as John said, you speed it up. But to get more aesthetic results you would need other manipulations too, such as elongation. I would imagine each quake as a chord, and as Petra says, each is likely unique. After all, no two snowflakes are exactly the same.

Russell, I do not think you will get a simple literal proportion per magnitude, though there would be nothing wrong with artificially doing so. How about it, Roger? You could add sound effects to your program, with higher magnitudes giving deeper sounds?...