Том 11, № 1 (2017)

Retrospective modeling of the sequences of shallow-focus weak earthquakes (M ~ 2.0–3.0) in Southern Sakhalin for the period of 2003–2014 is conducted using the method of self-developing process and the catalogue data of the local network. Mathematical models of the nonlinear increase of the cumulative shocks before strong (M = 4.6–6.2) events are constructed. Short-term forecasts of the parameter T₀ (origin time of strong aftershocks) are obtained with a high degree of accuracy. The stability of the solutions obtained by varying the duration of the observation interval of catalogue data is shown. A gradual decrease in the error in the prediction of the T₀ parameter is achieved as we approach the end of the processing interval to the time of the main shock. Although the errors in prediction in the retrospective version are no more than one day, the real evaluation of the accuracy can only be obtained in the practice of real predictions. Meanwhile, we have demonstrated the possibility in principle of the short-term prediction of strong shallow-focus earthquakes in Southern Sakhalin.

The collected GPS/GLONASS data allow us to reveal new information on the recent geodynamics of the Kuril Island arc. The maximum deformation stress accumulates in the southern and northern parts of the study area, while a long fading transition process of postseismic motions is observed in the central segment of the Kuril arc as a result of the 2006–2007 great Simushir earthquakes of M_w = 8.3 and M_w = 8.1. We have succeeded in revealing the recent interplate coupling geometry of the Pacific and the North American lithospheric plates and also in estimating the seismic potential of different segments of the Kuril subduction zone.

Tsunamis are reconstructed on the basis of distribution of tsunamigenic sediments in coastal lowland sections. Reflections of anomalous tsunamis are recorded in detail in the lacustrine–boggy sections of the Lesser Kuril Ridge, while only fragments of these sediments have been found on the islands of the Greater Kuril Ridge. The distribution and composition of the sediments left by recent large-scale tsunamis (locally documented 1994 and 1894 Shikotan tsunamis and transoceanic 2011 Tohoku tsunami) are analyzed for the purpose of understanding deposition features during large and megatsunamis. Interregional correlation of the events during the last ~2.5 kyr is carried out with estimation of their scales. It is established that large events took place in the 17th and 18th centuries and approximately at 1.0, 1.4–1.6, 1.7–1.8, and 2.0–2.1 ka ago. New data on large tsunami chronology since the Middle Holocene are presented. A unique natural peatland section with abundant tsunamigenic sand layers is studied on the Pacific side of Zelenyi Island (Rudnya Bay), where deposition continued through the entire Holocene. The largest tsunamis which happened on the South Kuril Islands during the last ~7.5 kyr and can be classed as megatsunamis are revealed.

This paper presents the results of reconstruction of the modern tectonic stress field of the northern part of the Kuril–Okhotsk region prior to the May 24, 2013 deep-focus earthquake. This earthquake is the strongest deep-focus earthquake not only in the Okhotsk region but also in the world over the entire period of seismic observations. The tectonic stress field is reconstructed using the method of cataclastic analysis (MCA) of the earthquake source mechanism data. New data on the depth variations of regional tectonic stress field are obtained.