Rock Deformation Measurements and Connection with Major Seismicity
Abstract:The European network of tiltmeters – vertical static pendulums – was established in 2007 (Neumann and Kalenda 2010, Kalenda et al. 2012). Two pendulums were installed in the Prokop gallery in Příbram in the depth of 2 m and 96 m below the surface. Another pendulum was installed in cave No.13C in the Moravian Karst at a depth of 60 m below the surface. In 2014, the whole network consists of 12 pendulums at 9 localities in 6 countries (Czech Republic, Slovakia, Slovenia, Ukraine, Russia and Armenia). The best pendulums operate deeper than 60m below the surface under special conditions without traffic, wind, temperature changes and visitors.
Each locality is specific – its reaction to changes of the tectonic stress depends on local tectonic conditions. The pendulums close to the NW-SE active faults are sensitive to “the Indonesian” direction. In the Ida mine we observed changes of the tilt and tilt noise (defined as a variation of the tilt in the 30-minute window) before Chile Feb 2, 2010 (M8.8), Sumatra Apr 11, 2010 (M7.8), Nicobar Isl. June 12, 2010 (M7.5), Sumatra Apr 11, 2012 (M8.4) and Iran-Pakistan border Apr 16, 2013 (M7.8) earthquakes. The pendulum in cave No.13C, which is close to the N-S active fault, is very sensitive especially to deep earthquakes from the Kuril-Kamchatka area. We observed variations of the tilt and especially peeks around noon and a high tilt noise before the earthquakes at the Kuril Islands, Nov 24, 2008 (M7.3), the Okhotsk Sea, Aug 12, 2012 (M7.7) and the Okhotsk Sea, May 24, 2013 (M8.3). The Tohoku earthquake (M9, Mar 11, 2011) was not preceded by any significant tilt anomalies on pendulums in Central Europe, although there were observed anomalies of water level and radon even a month before the mainshock (Kolínský et al. 2013, Briestenský et al. 2014).
With the exception of the tilt anomalies before-, co- and after the mainshock, we recognized a high tilt noise after the biggest earthquakes, which correlated well with the secondary microseisms and the deformation rate (Holub et al. 2013). Such “deformation waves” could trigger the volcanic activity on Iceland in 2010 and 2011 after the Chile and Tohoku earthquakes (Kalenda and Neumann 2012).