Abstract
The study has been done on the orientation of the principal axes of tectonic stress field at intermediate depths of earthquakes of the southern flank of the Kuril-Kamchatka subduction system separately for the upper and lower double seismic focal zones. Use has been made of the NIED and GlobalCMT catalogue data. The computation-based results are presented on schemes of the stressed state of the investigated areas and in tables. In the context of the southern Kuril Islands, evidence has been provided for predominance of the maximum compressive stresses along the slab plane in the upper layer and minimal compressive stresses (deviation extension) in the lower layer. However, the principal axes of maximum and minimum compression are displaced in direction relative to the slab dip: by 30–40° counterclockwise for the compression axis in the upper layer, which coincides with the direction of plate movement, and clockwise for the extension axis in the lower layer. This might be caused by the right-lateral strike-slip component of the Pacific Plate subduction. Unlike the general trend, the orientation of the principal axes of the stress field beneath the central Hokkaido-related segments in the upper layer is almost identical to that in the lower layer. There have also been found the segments exposed to shear stress, with the most extensive located opposite the northern Kunashir Island and beneath the southern Hokkaido Island. The results obtained for major large groups of clusters show good accordance with those published by other authors. The discrepancies relate primarily to small groups of isolated clusters showing local stress field heterogeneities.
Highlights
The study has been done on the field of the principal tectonic stresses direction at intermediate depths of earthquakes of the southern flank of the Kuril-Kamchatka subduction system separately for the upper and lower double seismic focal zones
Use has been made of the NIED and GlobalCMT catalogue data
In the context of the southern Kuril Islands, evidence has been provided for predominance of the maximum compressive stresses along the slab plane in the upper layer and minimal compressive stresses in the lower layer
Summary
Цветом показан кинематический тип сейсмодислокации в очаге относительно слэба. Зелеными линиями показаны изолинии глубины верхней границы сейсмофокальной зоны согласно модели Slab2 [Hayes et al, 2018], стрелками и зеленым пунктиром – направление поддвига Тихоокеанской плиты. Согласно модели Slab2 [Hayes et al, 2018] этот уча сток слэба на южном фланге Курило-Камчатской суб дукционной системы относительно ровный Чтобы учесть это изменение наклона, а также для удобства рассмотре ния территория разделена поперек островной дуги на шесть сегментов «a» – «f» шириной около 150 км. За на правления осей новой координатной системы приня ты простирание слэба для всех сегментов «a» – «f» Для упрощения задачи было сделано допущение, что граница между слоями параллельна верхней границе сейсмофокальной зоны, плоскости, примерно согласующейся с моделью Slab2 [Hayes et al, 2018], и ортогональной оси h.
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