The unusual case of the ultra-deep 2015 Ogasawara earthquake (MW7.9): Natural time analysisP. A. Varotsos, N. V. Sarlis, E. S. Skordas, Toshiyasu Nagao and Masashi KamogawaEPL, 135 4 (2021) 49002DOI: https://doi.org/10.1209/0295-5075/135/49002