The January 2007 windstorm and its impact on microseisms obsered in the Czech Republic

Abstract

The paper is intended as an analysis of microseismic vibrations before and during the windstorm named “Kyrill”, which occurred in mid-January 2007. Microseisms were observed at the Ostrava-Krásné Pole (OKC) seismic station, where broadband seismographs were installed. Two maxima in the graph of displacement amplitudes, around 2 µm, were documented during six days (January 16 through 21, 2007) of observation, whose predominant periods did not exceeded T = 4–8 s. The firs maximum of the displacement amplitudes, detected on January 17 around midday, represented the manifestation of the microseismic storm induced by the barometric depression over the northern part of the Atlantic Ocean. The second, which appeared during the night of January 18–19, 2007, coincided with the progress of the windstorm across the territory of Northern Moravia and Silesia (Czech Republic). Since microseisms are generally considered to be Love and Rayleigh surface waves, their propagation velocity from the source through the superficia layers of the Earth´s crust to the inland of the European continent is multiply higher than the rate at which ocean waves and/or the windstorm spreads in the atmosphere. Therefore, the maximum of the displacement amplitudes corresponding to the microseismic storm preceded the second maximum caused by the windstorm “Kyrill”. In conjuction with the study of microseisms also some meteorological data are taken into account when the results of both observatory research programs were interpreted. The comparison of the wind speed graph with the graph of amplitudes of microseisms proves that the maximum wind speed of about 20 m/s corresponded to the second maximum of the displacement amplitudes.

Keywords

• windstorm
• seismic waves
• kyrill