  The Carlson-Langer model is a deterministic model of earthquakes. There were
many investigations of this model, but its complicated spatio-temporal dynamics
is not yet completely understood. We again study the model equation
numerically, and obtain two new results. Firstly, we try to understand the
complicated dynamics from the viewpoint of spatio-temporal intermittency. We
study the intermittent dynamics of a two-block system using a one-dimensional
map, which is useful for understanding an intermittent spatio-temporal chaos in
larger systems. Large slips occur intermittently after repeated small slips
when the parameter of the velocity weakening friction is large. Small slips
reduce the spatial irregularity of block displacement, and large slips occur on
a relatively flat configuration of blocks. Secondly, we study the effect of
spatial heterogeneity such as asperity using percolation clusters. We show the
numerical results of the slip-size distribution in the block-spring model on
percolation clusters, and find that the b parameter for the magnitude
distribution is close to 2/3 when the velocity weakening parameter is
intermediate.
