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Abstract

Six degree-of-freedom (6-DoF) ground motion measurements are recorded combining a rotational sensor and a seismometer. This allows in principle to determine the back azimuth of a moving source using a single point measurement. We investigated the movement of a vibroseis truck operated from 20 November 2019, 11:00 UTC to 21 November 2019, 14:00 UTC. We used 480 Sweep signals each lasting 15 seconds in a broad frequency range between 7 to 120 Hz from 160 different locations. We derived back azimuths for each sweep from 6 DoF data and calculated root mean square amplitudes of each ground rotation component. We repeat this procedure for 5 other nearby rotational sensors of the same type. Within the first day, the North pointing rotation axis of all sensors recorded larger amplitude signals at the beginning of the experiment proving that SV shear wave energy is dominant. Later, we observed larger amplitudes on the East component following the direction of the moving vibroseis truck. Conventional methods to locate a seismic source rely on the P wave polarization or arrival times measured with a network of stations. In this study we used S waves to track the vibroseis truck movements since rotational sensors are not sensitive to P wave motions.