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Abstract
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Rotational effect of earth shaking is an emerging field for studying all aspects of rotational ground motions induced by earthquakes, explosions, and ambient vibrations. It is an interesting field for a wide range of geophysical disciplines, including strong-motion seismology, broadband seismology, earthquake engineering, earthquake physics, seismic instrumentation, seismic hazards, seismotectonics, and geodesy. The seismic waves that are radiated out from the earthquake source always travel through the entire Earth and usually are measured at the ground surface by a seismometer which consists of three orthogonal components (Z (vertical), N (north-south), and E (east-west) or R (radial), T (transversal), and Z (vertical)). However, a complete representation of the ground motion induced by earthquakes consists not only of those three components of translational motion, but also three components of rotational motion plus six components of strain. The main objective of this study, is investigation the rotational components of deformation using seismic data in Sought Khorasan Zone. Historical evidence shows that major part of deformation (50-100 percent) is caused by seismic events which occurred in this zone. Therefore, the data of earthqukes were used in order to calculate seismic displacement and tensor rotational strain. The rotational strain tensor results provides the contribution of the rotation effect around the vertical, NorthSouth and East-West. Finally we found a rotation rate of about 2.5 degrees per million years around the vertical axis that is compatible with the result of the studies of other researchers with other methods. The results of this study can be used to complete those with other methods to improve information of the deformation in this zone.
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