Ring-shaped seismicity structures in the region of Kamchatka: possible preparation for great earthquake

Abstract

We have been studying some seismicity characteristics in the region of Kamchatka region. It was established that two pairs of ring-shaped seismicity structures at depths of 0-33 and 34-70 km have been formed here in 1973-2018 prior to large earthquakes (05.12.1997 г., Mw=7.8 and 20.12.2018, Mw=7.3). Ring-shaped structures are characterized by threshold magnitude values (Mt1 and Mt2 correspondingly) and also big axes length (L1 and L2). Ring-shaped structures were identified in the area to the east and northeast of Petropavlovsk-Kamchatskiy city, where no great earthquakes have occurred during more than 60 years (ring-shaped structure was identified also in the depth range of 71-110 km here). Earlier, correlation dependences of Mt1 and Mt2 parameters on Mw values of major earthquakes for the west of Pacific were creating. Using these dependencies, the magnitude of possible great earthquake in this area was estimated as Mw=8.6±0.2. Besides that, a conclusion on the source depth of such event was drawing on the base of the analysis of three ring-shaped structures. The reasons for ring-shaped structures formation in different depth ranges of the subduction zones are discussing.