The unusual case of the ultra-deep 2015 Ogasawara earthquake (MW7.9): Natural time analysis P. A. Varotsos, N. V. Sarlis, E. S. Skordas, Toshiyasu Nagao and Masashi Kamogawa EPL, 135 4 (2021) 49002 Published online: 25 October 2021 DOI: 10.1209/0295-5075/135/49002