Modeling geomagnetically induced currents in Hokkaido, Japan Original Research Article

In this paper a model for computing geomagnetically induced currents (GIC) from local geomagnetic field observations carried out in Hokkaido, Japan is constructed. The model is composed of system parameters mapping the horizontal geoelectric field to GIC and of 1D conductivity model. A rigorous model validation is used to show that the model reproduces the observed GIC with a very good accuracy. Statistical occurrence of GIC is computed using the constructed model and geomagnetic field recordings covering years 1986–2008. The modeled GIC is used to generate a list of 10 largest GIC events in Hokkaido, Japan. It is found that the 10 largest events between 1986 and 2008 were associated with various phases of coronal mass ejection driven major geomagnetic storms. It is also shown that although smaller GIC are fairly common, the largest possible GIC are likely limited to the amplitudes of the order of 10 A. The constructed 1D ground conductivity model is interpreted in the context of the local geological setting and it is shown that the subduction zone dynamics likely play an important role in the observed GIC and geomagnetic field characteristics. Crustal conductor associated with the subduction zone is the cause for unusual direct relation between GIC and the local geomagnetic field rather than its time derivative and GIC.