Preseismic ULF electromagnetic effect from observation at Kamchatka

Abstract. Some results of ULF magnetic field observation at Karimshino site (Kamchatka, Russia) since June 2000 to September 2001 are presented here. Using case study we have found an effect of suppression of ULF intensity about 2–6 days before rather strong and nearby seismic shocks (magnitude M = 4.0 – 6.2). It is revealed for nighttime and horizontal component of ULF field (G) in the frequency range 0.01 – 0.1 Hz. Then we prove the reliability of the effect by computed correlation between G (or 1/G) and specially calculated seismic indexes K_s for the whole period of observation. Basing on the simple criteria we conclude that reliability of seismo-associated ULF suppression effect is comparable with well-known effect of connection between ULF variation and K_p index of global magnetic activity. It seems the reason of suppression is located at the atmosphere or ionosphere but not in the ground medium.