Simultaneous observations of ionospheric disturbances from VLF transmitter signals and surface displacements from GPS related to inland earthquakes over Japan

Ionospheric anomalies have been reported for years before major seismic activities by using VLF transmitter signals. Although possible generation mechanisms of the precursory perturbations have been proposed such as anomalous electric field and atmospheric waves originated around the future epicenter, the experimental evidence indicating the coupling between the lithospheric activities and overlaying ionosphere before seismic events has not been confirmed. In this paper we analyze the VLF transmitter amplitude data from UEC´s VLF observation network identifying the ionospheric perturbations together with frequency dependent filtered surface displacement data from high density GPS network for inland earthquakes in Japan during several consecutive years to study the LAIC mechanism. We found that both ionospheric perturbations and surface displacements occurred almost simultaneously about one week before for some of the shallow earthquakes indicative of coupling between the precursory ground movement and relevant ionospheric perturbations. Either ionospheric or GPS anomalies were also found for other earthquakes. We are also going to discuss the significance of types of earthquakes for LAIC mechanism.