Actually, earthquake magnitude can be projected to negative numbers. It's well defined but it stops describing earthquakes. For instance, a -3 magnitude earthquake is the energy released by a cat knocking your cell phone off of a nightstand. (see page 290 of this book). Pretty sure the others are also logarithmic scales which are well-defined for any negative number. It just so happens that those negative numbers don't describe anything we care to describe with those scales.