Some possible correlations between electro-magnetic emission and seismic activity during West Bohemia 2008 earthquake swarm

Abstract

Abstract.A potential link between electromagnetic emission (EME) and seismic activity (SA) has been the subject of scientific speculations for a long time. EME versus SA relations obtained during the 2008 earthquake swarm which occurred in West Bohemia are presented. First, a brief characterisation of the seismic region and then the EME recording method and data analysis will be described. No simple direct link between EME and SA intensity was observed, nevertheless a deeper statistical analysis indicates: (i) slight increase of EME activity in the time interval 60 to 30 min before a seismic event with prevalent periods about 10 min, (ii) some gap in EME activity approximately 2 h after the event, and (iii) again a flat maximum about 4 h after the seismic events. These results qualitatively correspond with the observations from other seismically active regions (Fraser-Smith et al., 1990). The global decrease of EME activity correlating with the swarm activity decay was also observed. Due to the incomplete EME data and short observation time, these results are limited in reliability and are indicative only.

5 years of measurement of electromagnetic emission in West Bohemian seismoactive region

“…earthquake preparation, relaxation and healing (c.f. Kolář, 2010) and the effect was found to be qualitatively consistent with results published by Fraser-Smith et al (1990) (quoted also in Johnston, 1997 andKolář, 2010). However the effect can be hardly observed for swarm 2011 and is not observed for 2013 year swarm, when they are processed in the same way.…”

“…We may speculate either that the 2008 year result is simply an accident, or that the swarms in 2011 and 2013 years even if still pronounced, were weaker and weaker and that they were not strong enough to excite the effect. On the other hand, the effect observed in 2008 year swarm seemed to be rather excited by moderated events (Ml ~ 2) then with the strongest ones (see Kolář, 2010). The two later swarms, even if they are about similar location, were after all situated rather northerly (see Fig.…”

“…The early analysis showed, that the instrument behave as a "poor quality" seismometer, i.e. there are strong signals which exactly correlate with P and/or S waves arrival at the station, we call this anomaly "microphone effect" (it was already documented in (Kolář, 2010)). We tested EME data on occurence of any signal at the time of earthquake outbreak (i.e.…”

“…Brief overlook about theses swarms is given in Table 1 and in Figure 3. The results of processing of the data recorded during the 2008 swarm were already published in Kolář (2010). As secondary extremes of EME signal cannot be directly interpreted, they are treated statistically in our study.…”

“…from special issues of Studia Geophysica et Geodetica (2000Geodetica ( , 2008Geodetica ( , 2009 or from recent review by Fischer et al (2013), as the most recent examples of variety of performed studies it can be mentioned e.g. Kolář (2010), Kolář et al (2011), Kolář and Růžek (2012), Chum et al (2012), Růžek et al (2012).…”