Is there a formula to compute the destructiveness of an earthquake?
The 'destructiveness' is a function of local geology and hydrogeology, type of earthquake, depth of earthquake, local population density, and whether the local builders paid attention to the appropriate building codes. So no, there isn't an equation for destructiveness. However, you can estimate the local intensity (at the surface) from the magnitude. The mathematical approach is given in the APPLICATIONS OF EXPONENTIAL AND LOGARITHMIC FUNCTIONS for earthquakes.