  An improved version of the Olami-Feder-Christensen model has been introduced
to consider avalanche size differences. Our model well demonstrates the
power-law behavior and finite size scaling of avalanche size distribution in
any range of the adding parameter $p_{add}$ of the model. The probability
density functions (PDFs) for the avalanche size differences at consecutive time
steps (defined as returns) appear to be well approached, in the thermodynamic
limit, by q-Gaussian shape with appropriate q values which can be obtained a
priori from the avalanche size exponent $\tau$. For the small system sizes,
however, return distributions are found to be consistent with the crossover
formulas proposed recently in Tsallis and Tirnakli, J. Phys.: Conf. Ser. 201,
012001 (2010). Our results strengthen recent findings of Caruso et al. [Phys.
Rev. E 75, 055101(R) (2007)] on the real earthquake data which support the
hypothesis that knowing the magnitude of previous earthquakes does not make the
magnitude of the next earthquake predictable. Moreover, the scaling relation of
the waiting time distribution of the model has also been found.
