Possible model of electromagnetic signals before earthquakes

Few days before many earthquakes a general change in the ratio of vertical to horizontal magnetic field components in the ULF band, often called “polarization”, has been observed that can be considered as a magnetic precursor of the subsequent earthquake. To explain such a specific behavior, we propose a simple model based on a linear current approximation depending on some assumption on the signal to noise ratio. This model is confirmed through a comparison that has been carried out between the experimental magnetic field data at Matsushiro (Japan, 1998.06.30, M=4.7) and Simeiz (Crimea, Ukraine, 1998.10.16, M=4.3 and 1998.10.18, M=4.3) earthquakes. About 1 – 2 days before these events we had recorded the anomalous decrease of the ratio of vertical to horizontal magnetic field components in Pc4 – Pc3 band. The NE-SW direction of the corresponding current linear model well agrees with the main tectonic feature of both seismogenic events. Additionally we also estimate the signal to noise ratio limits for the detection of ULF magnetic field components in Corralitos and Stanford campus for Loma Prieta (MS 7.1, 1989) earthquake