This study is assessing the tsunami hazard for a segment of the Kamchatka western coast around the Oktyabrsky Spit. The motivation is to ensure transportation access to the village of Oktyabrsky and to the fish processing facilities situated on the Spit. The hazard estimates were derived by the worst case method. An analysis of seismicity and historical data on tsunami occurrences in the Sea of Okhotsk resulted in identification of two tsunami-generating zones that constitute threat to the Oktyabrsky coast segment, with a set of model tsunami-generating earthquakes being determined for each zone. For this set of models we conducted numerical modeling for tsunami generation and propagation, resulting in a selection of model sources that would pose the greatest threat to the coastal strip of interest. The next step involved refining calculations for these sources using a sequence of nested grids to find the parameters of tsunami impact on the coast. The main results of the present study consist in identification of tsunami-generating zones that pose the highest threat to the Oktyabrsky coast, the selection of tsunami-generating model sources in these zones, and estimates of parameters that characterize extreme tsunami waves posing threat to this coast strip.

The article presents instrumental and macroseismic data on the Paramushir earthquake of March 25, 2020, ML=7.7, Mw=7.4, discusses its tectonic position and features of the aftershock process. This event is the strongest instrumentally recorded earthquake with a source located in the Pacific lithospheric plate in the area of the Northern Kuril Islands. The focal mechanisms and moment magnitude values Mw of the Paramushir earthquake and its strongest aftershocks were obtained using an original method for calculating seismic moment tensors, de veloped at the Кamchatka branch of Geophysical Survey RAS. The Paramushir earthquake was felt in 60 settle ments in the Kamchatka and the Sakhalin Regions, and was also noticed on the islands of Hokkaido (Japan) and Adak (USA). The maximum macroseismic manifestations were noted in the city of Severo-Kurilsk (Paramushir Island), I=6–7 points on the Seismic Intensity Scale 2017 (Russian building code GOST R 57546–2017); there were no casualties or destruction. A weak tsunami with a maximum observed wave height of ~50 cm was noted in the area of Severo-Kurilsk.

The strong Mw = 7.4 earthquake occurred on March 25, 2020 in the region of Northern Kuril Islands, with its epicenter on the ocean side of the Kuril-Kamchatka deep-water trench, to the east from its axis. The earthquake was felt on all the Kuril Islands, South and East Kamchatka, the maximum shaking was recorded in Severo-Kurilsk with intensity I = VI–VII. Distinct tsunami wave was also registered. In the article, this earthquake and its tectonic position are discussed in the context of the seismicity of the Kuril-Kamchatka arc. The actions of duty shifts in earthquake processing are described, and a detailed description of macroseismic effects is given. The results of the analysis of peak ground motion amplitudes, focal mechanisms and models of the source, tsunami propagation features are also shown. Coseismic displacements revealed by GNSS observation data are presented and compared with model data. Peculiarities and stages of the aftershock process are discussed and the size of the source area is estimated.

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.

A comparative study is performed of the effect an inorganic phosphate (Pi) has on the formation of hydrogen peroxide in aqueous solutions of 2 × 10−4 M adenine derivatives (AX), such as adenine, adenosine, and adenosine-5'-diphosphate, irradiated at 77 K by near-UV in the wavelength range λ = 260–400 and 290–460 nm. It is found that the yield of H2O2 in irradiated samples grows upon adding 5 × 10−4 M Pi. The yield of H2O2 is normally increased in the presence of NaCl, while a tenfold increase in [Pi] results in only a moderate rise in [H2O2]. It is shown that the effect irradiation has on the yield of H2O2 depends on both AX and the [NaCl] and [Pi] ratio. The obtained data are compared to the results from measuring the EPR spectra of irradiated solutions before defrosting. Possible mechanisms of photoinitiated processes of H2O2 formation in the studied systems are discussed.

The content of hydrogen peroxide in aqueous 2 × 10–4 M solutions of adenine (A), adenosine (Ado), and adenosine-5'-diphosphate (ADP) containing NaCl (0.1 M) and identical solutions containing ZnCl2 and CaCl2 additions near UV-irradiated at 77 K was determined. The introduction of bivalent metal ions (2 × 10–4 M) differently affected the yield of H2O2 in different compounds. In A solutions, the addition of Zn2+ ions led to a yield of H2O2 increased more than 20-fold, and the addition of Ca2+ led to a 1.4-fold increase. In the case of Ado, the yield of H2O2 decreased 2.2- and 2.9-fold when Zn2+ and Ca2+ ions, respectively, were introduced in solutions. The addition of Zn2+ to ADP solutions led to a ~1.8-fold increase in the yield of H2O2. A comparison of the results of H2O2 determination in the systems with the estimated integral intensities of the EPR signals (IntS) of the irradiated solutions before defreezing (and estimated contents of the components of these spectra obtained by simulation) indicated that the main products of H2O2 formation in the systems were aggregates of adenine derivatives that formed during the freezing of aqueous solutions.

The paper presents the first results of integrated research of the strong seismic event (Uglovoye Podnyatiye earthquake (UPE) with a magnitude of Mw=7.3) that occurred on December 20, 2018 in the junction zone between the Kuril-Kamchatka and Aleutian island arcs. The authors has provided macroseismic information about the UPE, calculated peak ground accelerations and the seismic moment tensor, and described briefly the forshock and aftershock processes, as well as summarized data on earthquake precursors. UPE was reported to be felt at distances of up to 500 km. The maximum shaking was recorded as I = 5–6 at an epicentral distance of Δ~90 km on Bering Island, where the maximum instrumental acceleration of ~60 cm/s2 was recorded. It is shown that foreshocks remote in time occurred 2 years prior to the UPE. The distinctive grouping of the aftershocks in three spatially isolated clusters characterized by different parameters of the seismicity time course is related to the long and intense aftershock process of the UPE. The strongest aftershock had magnitude ML=6.6, another 25 events corresponded to ML≥5.0. UPE was preceded by precursor anomalies in the parameters of geophysical fields and the seismic process. The authors estimated the size of the UPE rupture, the depth of the equivalent source, the magnitude of the focal slip, and the duration of the rupture. The seismic moment tensor UPE has a large non-dipole component.

The results of comparing the data of two methods of geophysical monitoring of the stress-strain state of a borehole of the geoenvironment in the zone of Petropavlovsk-Kamchatsky geodynamic testing site to the data on the focal mechanisms of earthquakes that occurred in this zone on the same time interval are presented.

We present the results of the long-term study which make it possible to assess the possibilities of two methods used at the Petropavlovsk-Kamchatskii geodynamic site (Russia) for continuous monitoring of the stress–strain state of geoenvironment. The methods are based on the borehole geoacoustic measurements and electromagnetic measurements with underground electric antennas. Combined with hydrogeochemical and hydrogeodynamic borehole measurements, these methods allow monitoring the changes in the parameters of geological environment and identifying the stages in the changes of its stress–strain state. As the examples, we present the results of the measurements in the time vicinities of the strongest seismic events that occurred during the period of joint borehole geoacoustic and electromagnetic measurements at the Petropavlovsk-Kamchatskii geodynamic site. We also analyze the data obtained in the time vicinities of the Tohoku mega-earthquake (March 11, 2011, Japan, Mw 9.1) and a close strong Zhupanovskoe earthquake (January 30, 2016, Mw 7.2) that occurred at the epicentral distances R = 107 km from Petropavlovsk-Kamchatskii. It is shown that the discussed methods are promising for medium- and short-term forecasting of the earthquakes.

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.

Приводятся результаты сопоставления данных двух методов скважинного геофизического мониторинга напряжённо-деформированного состояния геосреды в зоне Петропавловск-Камчатского геодинамического полигона с данными по механизмам очагов землетрясений, произошедших в этой зоне на том же временном интервале.

According to the available data from the Kamchatka Regional Catalog, in the southwestern part of the Kamchatka region, deep earthquakes systematically occurred away from the main seismic focal zone. The paper shows that these anomalous events in the catalog are an artifact caused by the ambiguity of solutions for the hypocenters of earthquakes, which occur in the region located away from the seismic network. The results can be improved by eliminating the station data with the maximum residuals of the arrival times of the waves. Hypocenters were relocated for 102 deep earthquakes from an extended area covering anomalous events. Most of the new solutions lie within the Kamchatka seismic focal zone. The corresponding changes have been added to the Kamchatka regional catalog.

Comparative results are presented from detecting hydrogen peroxide (H2O2) in aqueous solutions of adenine derivatives irradiated at 77 K in the near-UV range of wavelengths (λ = 260–400 and 290–460 nm). It is shown that the efficiency of H2O2 formation, estimated from the ratio of [H2O2] to the integral intensity of EPR signals observed in the irradiated samples, grew in the latter case. Based on the literature data, this increase is assumed to be due to specific features of the photoexcitation of aggregates of adenine derivatives that form in frozen aqueous solutions.

The content of hydrogen peroxide is determined in NaCl-containing (0.001–0.1 M) aqueous solutions of adenosine-5'-diphosphate (ADP) and adenosine (Ado) irradiated with near-UV light at 77 K. The obtained data are compared to estimates of the integral intensity (Int) of the EPR signals from the irradiated solutions prior to their thawing and the contents of different components in these spectra (including peroxyl free radicals), calculated by analyzing these spectra from their modeling. It is found that at a low content of photosensitizers (2 × 10 −4 M), the relationship between [H 2 O 2 ] and Int differs for ADP and Ado (a positive linear correlation in the case of ADP and a decreasing nonlinear dependence for Ado). It is assumed that these differences are due to the combination of two main factors: (1) the difference between the self-association constants ( K sa ) of ADP and Ado and (2) the effect of the freezing process, during which added NaCl exerts a disaggregating action of the formation of ADP and Ado associates. The relation between [H 2 O 2 ] and the EPR signal characteristics differs for high (1 × 10 −3 M) and low (2 × 10 −4 M) concentrations of photosensitizers, suggesting there are two paths of hydrogen peroxide formation in the investigated systems. According to the first path, H 2 O 2 is formed during thawing as a result of interaction between peroxyl radicals O 2 -· and HO 2 · that accumulate during irradiation. According to the second path, the formation of H 2 O 2 is direct (without releasing peroxyl radicals into the medium). This probably occurs inside aggregates of adenine derivatives, which form upon freezing the solution. In both cases, adding CaCl 2 to test solutions of Ado and ADP ([CaCl 2 ] = 0.1–0.2 × [NaCl]) results in a substantial drop in the yield of H 2 O 2 .

This is the second part of an report of Chebrov et al. on notable events in Kamchatka in 2013 for the Summary of the Bulletin of the International Seismological Centre including the largest deep-focus Sea of Okhotsk earthquake from 24 May 2013 with a magnitude of Mw=8.3.