The aim of this study is to investigate a wave dynamics and size scaling of
avalanches which were created by the mathematical model {[}J. \v{C}ern\'ak
Phys. Rev. E \textbf{65}, 046141 (2002)]. Numerical simulations were carried
out on a two dimensional lattice L×L in which two constant thresholds
EcI=4 and EcII>EcI were randomly distributed. A density
of sites c with the threshold EcII and threshold EcII are
parameters of the model. I have determined autocorrelations of avalanche size
waves, Hurst exponents, avalanche structures and avalanche size moments for
several densities c and thresholds EcII. I found correlated avalanche
size waves and multifractal scaling of avalanche sizes not only for specific
conditions, densities c=0.0, 1.0 and thresholds 8≤EcII≤32, in
which relaxation rules were precisely balanced, but also for more general
conditions, densities 0.0<c<1.0 and thresholds $8\leq E_{c}^{II}\leq3 in
which relaxation rules were unbalanced. The results suggest that the hypothesis
of a precise relaxation balance could be a specific case of a more general
rule