Ground-atmosphere-ionosphere Interactions Related to Earthquakes: How Can Earthscope Help?

Recent EARTHSCOPE activities have been concerned with monitoring earthquake-related parameters from using surface stress (INSAR) to deep borehole stress measurements (SAFOD). In this paper we draw attention to other parameters possibly related to earthquakes (EQ) that can be monitored from the ground and from space. Specifically, we propose to initiate a similar activity under TERRASCOPE or under some other future mission concept. Recent field studies and simultaneous satellite observations add confidence to reported observations of electromagnetic (EM) emissions before large earthquakes. There is likewise mounting evidence that, prior to seismic activity, electric fields are transmitted from the ground into the atmosphere, that thermal anomalies may become observable, that ions may be emitted from the ground, that the atmospheric conductivity is affected, that the ground potential may change locally or regionally, etc. Some authors have considered the possibility of an inverse connection from the atmosphere to the ground, causing seismic activity. Increased lightning activity, due to growing seismic activity, and the large currents thus induced may have an effect on the fracturing or microfracturing of rocks, focusing the EQ energy release [Pulinets, 2000]. Several ongoing international satellite missions, COMPASS (Russia, Poland, 2001), DEMETER (France, Japan, Russia, 2002) and VARIANT (European Space Agency, Ukraine, 2001), are aimed at retrieving ionospheric plasma anomalies that may be related to EQ activity (M>5). A recent experimental study [Freund, 2000] has indicated a direct connection between stress applied to rocks and the generation of charge carriers, causing electric currents and affecting surface potentials. These new results may intensify the interest in future similar studies. 1. Observable Changes on the Surface of the Solid Earth 1.1. Positive Holes Electrical phenomena preceding large earthquakes have been mentioned or described in the literature for centuries. What has been lacking, however, was a fundamental understanding of the nature of the electric charges in rocks and how they may be generated in the crust.