Book excerpt: This Research Topic is Volume II of a series. The previous volume can be found here: From Preparation to Faulting: Multidisciplinary Investigations on Earthquake Processes What happens before an earthquake occurs? What are the physical processes that take place in the Earth’s crust before the earthquake nucleates? How can we observe, describe, and model them statistically, numerically, and physically in multiscales from samples in laboratory to tectonic plate of earth? During the last few decades many efforts have been devoted to multidisciplinary studies in an attempt to answer these fundamental questions. Previously, the Institute of Physics of the Earth (IPE) model (dry) and Dilatancy Diffusion (DD) model (wet) were proposed for earthquake processes. Like Schrödinger's cat, earthquakes are unpredictable—according to the IPE model, yet they can be predictable—according to DD model. Recently, with advanced techniques, some scientists have declaimed that there are precursors to be used for earthquake forecasting, which offers new opportunities to study earthquake precursors.