Significant progress has been achieved on the study of electromagnetic phenomena in possible association with earthquakes during the last two decades since the 1995 Kobe earthquakes. It is a recent consensus that electromagnetic phenomena do appear prior to a large earthquake and some phenomena have been found to be statistically correlated with earthquakes. One of the most typical examples is ionospheric perturbation. But this book will shed a light on rather new and nonconventional electromagnetic phenomena: One is the ULF (Ultra low frequency less than 1Hz) depression (decrease in the amplitude of ULF horizontal magnetic field components) and another is ELF (extremely low frequency 1Hz