- © 2012
Lightning is a common meteorological phenomenon, and during thunderstorms numerous lightning strikes also influence seismic records worldwide. This can be due to electrical induction in the coils of a seismometer, electric fields influencing analog digital converters or other electronic components, or ground motions induced by the lightning strike itself and/or the acoustic coupling of the accompanying thunder. Most experimental seismologists have experienced the problems of strong electrical currents during lightning events damaging recording equipment or causing false triggers or alarms, a common problem in central Europe during the summer (i.e., Cranswick et al. 1985; Taylor et al. 1991; Gülkan et al. 2007; van Kamp et al. 2008; Kim et al. 2010; Zumberge et al. 2010). Even the most sophisticated lightning protection cannot always prevent equipment damage (Weichert and Henger 1976).
On 27 July 2011 a rare event occurred when lightning struck a tree on the grounds of the Seismological Observatory Bensberg (BNS), the central station of the local network of Cologne University (Hinzen and Reamer 2007; Hinzen and Fleischer 2007). The tree was located 53 m from a strong-motion station and a medium-period station with an active velocity proportional seismometer. In addition, analog monitors of a short-period passive seismometer and a long-period vertical component Sprengnether instrument recorded the incident. This contribution describes the event and gives an interpretation of the diverse records of this lightning strike extremely close to a seismic station.
THE LIGHTNING STRIKE
On 27 July 2011 a thunderstorm approached station BNS from the west. Dark storm clouds could be observed over the Lower Rhine Embayment at least one hour before the storm arrived. Heavy rain started at 14:20 UTC and several thunderclaps were heard. At 14:30 UTC, lightning struck the nearby compound of Kardinal Schulte Haus (Figure 1). Later, we learned that …