The particle-based Lattice Solid Model (LSM) was developed to provide a basis to study the physics of rocks and the non-linear dynamics of earthquakes. In previous work, intact material was modelled as particles bonded together by elastic-brittle links in a regular 2D triangular lattice and the model was applied to the study of fault zone evolution. A new modular and flexible LSM approach has been developed that allows different microphysics to be easily added and removed at the grain scale to enable the effect of different microphysics on macroscopic behaviour to be studied. The model is extended to allow three-dimensional simulations to be performed and particles of different sizes to be specified. The new model provides a basis to investigate nucleation, rupture and slip pulse propagation in complex fault zones without the previous model limitation of a regular low-level surface geometry.