卷 52, 编号 4 (2016)

The results of paleoseismological investigations to find the epicentral area of the Belovodskoe earthquake are presented. New data on prehistoric earthquakes have been obtained resulting from a seismic deformation study using trenching. It is found that seismic dislocations during the reactivation of the fault by the 1885 earthquake did not extend east of the Sokuluk River. In addition, the age and kinematic features of a paleoearthquake located in the area between the Sokuluk and Alamedin rivers are specified. This earthquake occurred in the interval of 887–1533 cal BC and was no less than 7.1 in magnitude. The minimal estimated earthquake source length is 32 km and the reverse-fault amplitude is 3.8 m.

Based on analysis of the empirical data on velocities of strong ground motions, the average shape of the velocity response spectrum was established for the first time. The basic parameters of the spectrum were studied, such as the logarithmic width and dynamic amplification factor β. As well, the asymmetry of the velocity response spectra and the steepness of their slopes were estimated. The mean values of all these parameters and corresponding standard deviations were determined. The results can be used for seismic treatment assessment.

An important task in seismic hazard assessment is estimation of the intensity and frequency of extremely strong earthquake effects, in particular, peak ground velocities (PGV). Earlier, a method was proposed to evaluate PGV values based on the magnitude of displacements of rock blocks (Rodkin et al., 2012). In this study, this method is used to analyze field data on the source zones of the August 19, 1992, M_S = 7.3 Susamyr earthquake and the January 3, 1911, M_w = 7.9 Kemin earthquake, and estimate maximum ground shaking at the upper construction site of the Upper Naryn series of hydropower plants, Kyrgyz Republic. It is shown that the resulting estimates are consistent with data obtained through other techniques. Therefore, the new approach can be recommended to estimate earthquake effects.

The parameters of the earthquake that took place February 3, 2015, near the city of Sumy, Ukraine, were calculated from an analysis of records obtained by both Russian and Ukrainian seismic stations (Poltava, Skvira, Nikolaev, Dneropetrovsk, and Desna). The calculated hypocenter depth of 54 km was verified by several approaches: isolation of deep PP, SP phases from the records of remote stations and solution of the kinematic problem for the Poltava station. The focal mechanism as shear with a complex fault component was determined by the first arrivals of P-waves. The data on the azimuthal travel-time curve confirm the focal mechanism. We have calculated the earthquake parameters; they are as follows: length gap L₁ = 8.08 km, L₂ = 6.68 km, a destruction rate of C = 2 km/s. We have obtained the dynamic parameters of the event. The calculated fault length (L = 5.46 km) within the accuracy limits of the method coincides with the early result obtained by the azimuthal travel-time curve. On the basis of these results, we suggest that elastic energy release and formation of the dislocations in the earthquake source occurred on a smooth, prefractured fault (σ_r > 0). Association of the hypocenter with the tectonic node of the northern marginal fault of the Dnieper–Donets graben and northern branch of Kryvyi Rih–Kremenchuk suture confirm this. Here, we observe a considerable Moho depth, structural alteration, and high gradients of the temperature and magnetic and electric rock properties in the lower Earth’s crust and upper mantle. These circumstances are favorable for the earthquake occurring here.