[M-IS04] Interdisciplinary studies on pre-earthquake processes

[MIS04-P04] Seasonal variations of Parkinson vectors in eastern China

*Zhiqiang Mao¹、Chieh-Hung Chen¹、Aisa Yisimayili² (1.China University of Geosciences、2.Earthquake Agency of Xinjiang Uygur Autonomous Region)

キーワード：Parkinson vector, Transfer function, Geomagnetic induction, Time-series analysis

Parkinson vectors (PVs, or induction vectors) derived from three-component geomagnetic data through vertical transfer functions (VTFs) are utilized to study the underlying conductivity. The PVs are mainly influenced by long-term effects that are underground conductivity structures and the geomagnetic coast effect. After the removal of the long-term effects, the PVs can be utilized to study the pre-earthquake conductivity anomalies. Recently, the seasonal effects have been observed in the PVs. However, causal mechanisms of the seasonal effects on the PVs are not fully understood. In this study, we utilize ten years data from 24 stations operated by the Geomagnetic Network of China to study the spatiotemporal characteristics of the PVs with a removal of the long-term effects. The analytical results show that the PVs with a removal of the long-term effects exhibit season variations that reach maximum in summer and winter. The phenomena are pronounced in lower frequency bands. The PVs at all stations consistently exhibit a counterclockwise rotation in June (summer), and a clockwise rotation in December (winter). The Inter-hemispheric field-aligned current in the ionosphere is one of the potential reasons to explain seasonal variations. This study finds that the Parkinson vectors are also affected by ionospheric current systems. When we study the pre-earthquake conductivity anomalies utilizing the VTFs, we should examine the influence of the seasonal effect on PVs.