Jaromír Knejzlík

Adaptation of the S-5-S pendulum seismometer for measurement of rotational ground motion

The Russian electrodynamic seismometer model S-5-S has been adapted for the measurement of rotational ground motion. The mechanical system of the original S-5-S seismometer consists of electrodynamic sensing and damping transducer coils mounted on an asymmetrical double-arm pendulum. This pendulum is suspended on a footing using two pairs of crossed flat springs, which operate as the axis of rotation. The pendulum is stabilised by an additional spring. The S-5-S can be used either as a vertical or as a horizontal sensor. The adaptation of the S-5-S seismometer described below involves removal of the additional spring and installation of an additional mass on the damping arm. Strain gauge angle sensors are installed on one pair of the crossed flat springs. The main dynamic parameters of the rotational seismometer created in this way, i.e. the natural period and damping, are controlled electronically by feedback currents proportional to the angular displacement and angular velocity, both fed to the damping transducer coil. This new seismometer, named the S-5-SR, enables measurement of the rotational component of ground motion around the horizontal or the vertical axes. The output signal from this S-5-SR seismometer can be proportional either to rotational displacement or rotational velocity.

Investigation of the Medieval Jeroným Mine Stability: Present Results from a Distributed Measurement Network

Jeroným is a sixteenth century mine situated in western Bohemia near Marianske Lazně. It is being prepared to be the base of a museum of medieval ore mining. As a source of information for investigation of stability of aged mining openings, a distributed measurement network (DMN) combined with seismic station has been built up gradually since 2004. DMN is equipped with sensors for measurement of mine water level changes (3 selected monitoring points), mine temperatures (2 points), rock massif joint aperture changes (4 points), cross-section convergence changes (2 points) and changes of rock massif stress tensor (2 points). Data acquisition unit of DMN is integrated into the seismic recording station that is equipped with data transmission via GSM network. Installation of all above mentioned sensors was finished in May 2009. A brief description of DMN and present results derived from the data obtained are described in the contribution. Monitoring of height changes of high inaccessible ceiling using laser distance meter and changes of stress tensor of rock massif are described in detail.

Coherence spectra of rotational and translational components of mining induced seismic events

Classical Russian S-5-S pendulum seismometer was modified for recording of the rotational components of ground motion. This seismometer was used for monitoring of mining induced seismic events in the Karviná region (Czech Republic). Together, three translational components of ground vibration velocity and one rotational component of ground vibration velocity around the vertical axis were recorded. Elaborated mining induced seismic events with epicentral distances up to 9 km were recorded in Doubrava locality, where the exploitation of black coal is still active. Numerical study of measured component attributes of mining induced seismic events is presented in this paper, namely squared Morlet wavelet coefficients and squared coherence spectrum between rotational and translational components. Squared Morlet wavelet coefficients enable to analyse time-and-frequency structure of elaborated signal, e.g. dynamics of the onset, evolution and disappearance of typical periods of the harmonic peaks, etc. Spectral measure of coherence was applied here for investigation of synchronization effects in 2-dimensional time series of translational and rotational components.