TY JOUR TI Epidemic type aftershock sequence exponential productivity KW Strong earthquakes KW aftershocks KW productivity KW ETAS model KW EP model KW forecast JO Russian Journal of Earth Sciences AU Baranov, S.V. AU Gvishiani, A.D. AU Narteau, C.. AU Shebalin, P.N. PY 2019 IS 19 PB Geophysical Center of the Russian Academy of Sciences