Lithosphere-atmosphere-ionosphere coupling associated with four Yutian earthquakes in China from GPS TEC and electromagnetic observations onboard satellites

During 2008–2020, four strong earthquakes occurred in Yutian, Xinjiang Uygur Automous Region, northwest China, in particular, two M7 + and two M6 + earthquakes demonstrating the high tectonic activity of this region. We systematically use multiple electromagnetic data from satellites and ground, such as GIM TEC (Global Ionospheric Mapping Total Electron Content) published by JPL (Jet Propulsion Laboratory), and the ULF (Ultra Low Frequency) electromagnetic waves and plasma parameters onboard DEMETER (Detection of Electro-Magnetic Emission Transmitted from Earthquake Regions), Swarm and CSES (China Seismo-Electromagnetic Satellite) satellites. The ionospheric perturbations were revealed frequently around the four case studies, but mostly within 10 days before, over the epicentral area, and sometimes over its conjugate region at southern hemisphere. The abnormal amplitude is quite larger in years with high solar activity than in those with low solar activity. We employ the SAMI2 model to simulate the variations from the effects of E × B under different plasma background in 2008 and 2014 to explain the great difference in different solar years. The similarity of the anomalies in this region demonstrates the higher electromagnetic and chemical emissions, implying that the electric field is possibly generated by the preparation of the seismic events in the epicentral area inducing the ionospheric disturbances above this area and its conjugate region through this coupling channel.