  Scaling analysis of seismicity in the space-time-magnitude domain very often
starts from the relation N(m,L)=a(L)*10**(-bm)*L**c for the rate of seismic
events of magnitude M>m in an area of size L. There is some evidence in favor
of multifractality being present in seismicity. In this case the optimal choice
of the scale exponent c is not unique. It is shown how different c's are
related to different types of spatial averaging applied to N(m,L) and what are
the c's for which the distributions of a(L) best agree for small L. Theoretical
analysis is tested using California data.
