Small-aperture-array translational and rotational seismograms from distant sources – An example of the Jan Mayen Mw 6.8 of 30 August 2012 earthquake

• The true backazimuth of a seismic wave estimated minimizing the radial-axis tilt rate.
• The phase velocity retrieved by matching transverse tilt rate and vertical acceleration.
• Collocated translational and rotational data enable to determine Rayleigh-wave dispersion.

We present the seismic rotation rate due to the earthquake of Mw 6.7 at the Jan Mayen island, obtained from broad-band seismograms at a distance of about 2740 km. The order of magnitude of the rotation rate amplitude is only 10−9 rad/s in this case. It is studied with a focus on rotation-to-translation relations. A joint analysis of the rotational and translational data allowed us to determine the true backazimuth and phase velocity of S- and Rayleigh waves. For the surface waves, we studied the frequency dependence of both the backazimuth and phase velocity (wave dispersion). The results are independently confirmed by a method based on time delays between translational records within a small-aperture array. Both methods revealed an unusual velocity drop in the dispersion curve between the periods of 18 and 22 s. This feature may be an indication of a low-velocity zone in the lower crust.