1. Geological Survey of Norway, Trondheim 7491, Norway
2. CAGE - Centre for Arctic Gas Hydrate, Environment and Climate, University of Tromsø, Tromso 9037, Norway.
3. Geophysical Observatory ‘Borok’, Borok, Yaroslavskaya Oblast 151742, Russia.
4. Institute of Geology and Petroleum Technologies, Kazan Federal University, Kazan 420008, Russia.