[1] We report the first consistent observations of rotational motions around a vertical axis induced by distant large earthquakes. It is standard in seismology to observe three components (up-down, N-S, E-W) of earthquake-induced translational ground motions using inertial seismometers. However, only recently ring laser technology has provided the required sensitivity for observations of the theoretically predicted rotational part of ground motion generated by seismic waves in a wide distance range and frequency band. Here we show that the rotations observed are consistent in waveform and amplitude with collocated recordings of transverse accelerations recorded by a standard seismometer. This suggests that rotations may become a new observable for seismology and related fields with the potential of providing complementary information on earthquake source processes, structural properties, and ground shaking.

S U M M A R YIt has been noted by theoretical seismologists for decades that-in addition to translations and strains-the rotational part of ground motions should also be recorded. It is expected that collocated measurements of translations and rotations may (1) allow transformation of translational seismograms to the complete ground motion of an observation point; (2) help to further constrain rupture processes and (3) provide additional hazard-relevant information to earthquake engineers. The lack of instrumental sensitivity used to be the main obstacle to observing rotational motions. Recently, ring laser technology has provided the means to develop instruments that allow in principle the observation of rotational motions in a wide frequency band and epicentral distance range. Here we investigate whether this technologyoriginally designed for geodesy-is capable of providing accurate and useful observations for seismology. We report observations of rotations around a vertical axis of several earthquakes obtained by a 4 × 4 m ring laser installed in SE-Germany and compare them to collocated broad-band translations. Assuming plane transverse wave propagation, acceleration and rotation rate should be in phase and their amplitude ratio proportional to horizontal phase velocity. Here we show that most of the observations can be explained under these assumptions and that the collocated observations allow the estimation of wavefield properties (e.g. phase velocities, propagation directions), otherwise only accessible through seismic array measurements, polarization analysis, or additional strain measurements.

In this paper we investigate non-complete Sawtooth reconnection in ASDEX Upgrade tokamak.Such reconnection phenomena are associated with internal m/n=1/1 kink mode which does not vanish after the crash phase (as would be the case for complete reconnection). It is shown that this sawtooth can not be fully described by pure m/n=1/1 mode and that higher harmonics play an important role during the Sawtooth crash phase. We employ the Hamiltonian formalism and reconstructed perturbations to model incomplete Sawtooth reconnection. It is demonstrated that stochastization appears due to excitation of low-order resonances which are present in the corresponding q-profiles inside the 1 q = surface which reflects the key role of the 0 q value.Depending on this value two completely different situations are possible for one and the same mode perturbations: (i) the resonant surfaces are present in q-profile leading to stochasticity and sawtooth crash ( 0 0.7 0.1 q ≈ ± ); (ii) the resonant surfaces are not present which means no stochasticity in the system and no crash event ( 0 0.9 0.05 q ≈ ± ). Accordingly central safety factor value is always less than unity in case of non-complete sawtooth reconnection. Our investigations show that stochastic model agrees well with experimental observations and can be proposed as a promising candidate for explanation of the sawtooth reconnection.