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Currently, the most popular approach for assessing the tsunami hazard on a coast is the PTHA (Probabilistic Tsunami Hazard Assessment). In this preliminary study, we develop one of the variants of the SPTHA (Seismic PTHA) method, adapted to solving local tsunami zonation problems for near-field sources. The approach is applied to assessing the tsunami hazard of the Bechevinskaya Cove located on the eastern coast of the Kamchatka Peninsula in the northern part of Avachinsky Bay. We propose the method, algorithms and results of probabilistic assessment of the cove's tsunami hazard in order to determine the safest water areas, in which the values of the intensity measures (IMs) of tsunami will not exceed the specified threshold values with the given Average Return Periods (ARPs). The method includes analysis of seismotectonics of the region, construction of a catalog of model tsunamigenic earthquakes, determination of their statistical characteristics, scenario numerical modeling of the dynamics of tsunami waves, calculations of the values of IMs that can be exceeded with the given annual rates (ARs), namely, on average 1 time in 100, 500, 1000 years. Spatial distributions of the maximum wave heights and maximum velocities are provided for the ARs. Three configurations of the water area are considered, including the possibility of constructing protective structures, and conclusions are drawn about their influence on the tsunami hazard assessments in the cove. [ABSTRACT FROM AUTHOR]

Spectral characteristics of the medium around 23 digital strong-motion seismic stations of Kamchatka region have been studied from local earthquake data relative to a reference bedrock station (Petropavlovsk, PET). Spectra are determined by multiband filtering. In each band peak velocity amplitudes, levels of Fourier S-spectra and mean-square coda amplitudes were compared. Average Fourier spectra were obtained from S-wave energy using Parseval's equation. The difference in hypocentral distances for pairs of stations was compensated by empirical S-wave attenuation functions. Records of more than 300 events were processed, with M = 5--6 and hypocentral distances mainly 100--600 km. The spectral ratios estimated by the three methods show behavior diversity. Some non-rock stations show expected spectral characteristics at high frequencies. The conditions at other stations can be considered similar to those at PET. Some stations show amplifications of up to 10 times in the 20--30 Hz frequency range. In general, the obtained spectral characteristics within 3--5 Hz are consistent with the expected trends corresponding to known local geology around strong-motion stations. [ABSTRACT FROM AUTHOR]

The largest instrumentally recorded regional back-arc earthquake with MW = 7.8, MC = 8.2 occurred on July 17, 2017 on the Bering transform fault (the boundary between the Beringia minor lithospheric plate and the Komandorskii (Commander) block of the Aleutian island arc). This seismic event, called the Near Islands earthquake or Near Islands Aleutian earthquake, caused the ground to shake with intensity I = 5–6 on Bering Island and a small tsunami wave on the Near Islands. The specific aspects of the peculiarities of the pattern of seismicity of the northwestern segment of the Aleutian arc and the tectonic position of the Near Island Aleutian earthquake, the details of its prompt processing, macroseismic manifestations, analysis results of ground motion peak amplitudes, focal mechanisms, and earthquake source models are discussed. The coseismic displacements according to the GNSS data are presented. It is concluded that the source of the Near Islands Aleutian earthquake did not fill the seismic gap near the Commander Islands, and the possibility of the strongest earthquake hitting the northwestern part of the Aleutian arc remains. [ABSTRACT FROM AUTHOR]

We describe a procedure for mass determination of the 'source-controlled f'-an important though not conventional parameter of earthquake source spectrum, relabeled here as 'the third corner frequency,' f, and discuss the results of its application. f is the upper cutoff frequency of Fourier acceleration spectrum of a record of a local earthquake; both source and path attenuation contribute to f. Most researchers believe the role of attenuation (' κ' parameter) to be dominating or exclusive. Still, source effect on f is sometimes revealed. If real, it may be important for source physics. To understand better the f phenomena, the constituents of f must be accurately separated. With this goal, we process seismograms of moderate earthquakes from Kamchatka subduction zone. First, we need reliable estimates of attenuation to recover source spectra. To this goal, an iterative processing procedure is constructed, that adjusts the attenuation model until the recovered source acceleration spectra become, on the average, flat up either to f, or up to the high-frequency limit of the frequency range analyzed. The latter case occurs when f is non-existent or unobservable. Below f, the double-corner source spectral model is thought to be valid, and the lower bound of acceleration spectral plateau is considered as the second corner frequency of earthquake source spectrum, fc2. The common corner frequency, f, is also estimated. Following this approach, more than 500 S-wave spectra of M = 4-6.5 Kamchatka earthquakes with hypocentral distances 80-220 km were analyzed. In about 80 % of the cases, f is clearly manifested; the remaining cases show, at high frequency, flat source acceleration spectra. In addition, in about 2/3 of cases, f is clearly above f, showing that double-corner spectra may dominate even at moderate magnitudes. Scaling behavior was examined for each of the corners. The f vs. M trend is common and close to similarity ( f ∝ M), whereas the trends for two other corners ( f ∝ M; f ∝ M) dramatically contradict the concept of similarity. Physical interpretation of such a behavior is discussed. The origin of f is ascribed to existence of the lowermost wavelength/size of fault heterogeneity. Its dependence on M may reflect evolution of maturity of a fault in geological time. The approximate scaling f ∝ $$f_{c1}^{0.5}$$ suggests that during propagation of slip pulse over a fault, its width, assumedly related to 1/ f, grows in a stochastic manner; this reminds the random evolution of propagating boundary in the framework of the known Eden model of random growth. [ABSTRACT FROM AUTHOR]