Fig. 4.From: Barometric and magnetic observations of vertical acoustic resonance and resultant generation of field-aligned current associated with earthquakesPower spectral density of geomagnetic variation observed at Memambetsu observatory. Spectral peaks for 01:00–02:00 UT (red solid line) shows the three theoretically expected major peaks, i.e., at 265 s, 220 s and 185 s. The black lines indicate the PSD before the earthquake. Note that the unit of the magnetic D component is in “minute” of angle and indicated as “a” for simplicity in the figure.Back to article page