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

Publication at Faculty of Mathematics and Physics |
2016

Abstract

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.