(a) Geomagnetic variation observed at Huancayo, Peru just after the origin time of the 2010 Chile earthquake. Oscillation is observed only in the declination (i.e., East-West component) which suggests the effect from a trans-equatorial field-aligned current generated in the ionosphere over the epicenter. The field-aligned current closes by the ionospheric current in the opposite hemisphere as depicted in Fig. 11(a). The arrival of the seismic wave was 8 minutes earlier (around 06:40 UT) than the onset of magnetic oscillation at 06:48 UT. (b) One second resolution geomagnetic data from Ancon observatory in Peru on the magnetic dip equator. The magnetic oscillation appears mainly in the D component, although a smaller variation is also seen in the Z (vertical) component. The small spiky variations in the H (horizontal) component are due to artificial noise caused by incomplete contact of the sensor cable. Note that the D component is expressed in units of nT.