Preface

Over the last several years, a lot of evidence has indicated that the earthquake generation process is a critical phenomenon, which culminates in a large event that corresponds to a critical point. A fundamental prediction of this hypothesis is that before the event reaches this critical point, a regional system of faults goes through a period of accelerating seismicity and seismic energy release, which forms the signature of the approach to the critical state. By the end of this stage, the critical point has been attained, and the stress exerted by friction on the shear zone, as well as the strain caused by an avalanche of fusing cracks, lead to irreversible instability and rupture. As a consequence of the processes prior to an event, changes in the physical/chemical state of the earth precede earthquakes. These variations can be called the ground precursors. There are a variety of such precursors, that are evident in their genesis, such as ground uplift and tilt, gas emissions, underground water-level fluctuations, changes in groundwater chemistry, and changes in electrical resistivity of the rock. [...]