A similar coast effect of geoelectric field directions in a three-block boundary zone during geomagnetic storm pulses

SUMMARY The coast effect, which enhances the geoelectric field during geomagnetic pulses at the sea–land boundary, is a classic topic in geomagnetism. This paper focuses on a similar coast effect observed at the boundary zones of three tectonic blocks, that is Alax, Ordos, and Tibetan. We used multiple geoelectric field data of the block boundary zone to obtain the surface current density and charge accumulation during two geomagnetic storm pulses in 2015. Then, we calculated the amplitudes of spherical elementary current systems (SECS) and telluric currents using the Markov Chain Monte Carlo method. The results indicate that the polarized directions of induced charges and currents are perpendicular to the block boundaries and tend to point towards the interior of the Tibetan block. Additionally, the Parkinson vectors of geomagnetic pulses point towards regions with lower surface resistivity. The amplitude of telluric currents at a depth of 10 km is one of the three SECS at 110 km, which locates sources in the boundary zone between Alax block and Tibetan block. Similar to the coast effect in the sea–land boundaries, we identify an analogous phenomenon in three-block boundary zone, demonstrating the accumulation of induced currents and charges during geomagnetic storm pulses. This study provides a novel empirical basis to promote our understanding of geomagnetic storm pulses induced charges enhancements at discontinuous conductivity interfaces on the Earth.