Central and South Kamchatka, separated by the Malko–Petropavlovsky Fault Zone, exhibit a complex geological structure shaped by the long-lived Pacific Plate subduction and associated magmatic and tectonic processes. Magmatism in the region is diverse in both composition and style, expressed through active and dormant volcanic complexes, monogenetic cones, calderas, and geothermal systems. However, the crustal structure governing this activity remains poorly resolved. We compiled three-component seismic records spanning 12 years from a permanent seismic network and six temporary deployments to perform ambient-noise tomography, deriving the shear-wave velocity (Vs) structure of the region. Using both vertical- and horizontal-component noise cross-correlation functions, we measured phase and group interstation velocities of the fundamental modes of Rayleigh and Love waves. To obtain robust phase-velocity estimates from horizontal-component cross-correlations, we expended and validated the Stockwell–Bessel transform method. We then inverted the extracted dispersion curves using a direct three-dimensional Bayesian Monte Carlo approach, obtaining Vs distribution and uncertainties down to a depth of 55 km. Our model images several major active fault zones and reveals previously unidentified fault structures. Beneath active volcanoes, we identify multilayered magmatic systems spatially associated with fault zones. Moreover, we imaged previously unreported magmatic structures beneath the inactive Opala and Vilyuchinsky volcanoes, as well as beneath the Sredinny Ridge. These results provide valuable insights into the tectonic framework, magmatic systems, and their interactions, illuminating the crustal sources of recent volcanism in Central and South Kamchatka.

This article presents data on the MW 8.9 Kamchatka earthquake of July 29, 2025, compiled by the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences (KB GS RAS) as of December 31, 2025. The Kamchatka earthquake is one of the largest seismic events in the history of instrumental observations. To date it ranks as the sixth most powerful event ever recorded in the world. The rupture zone, estimated based on the aftershock area, is 580 × 180 km and roughly coincides with the source area of the Great Kamchatka Earthquake of November 4, 1952 (MW 9.0). The 73-year gap between these two megathrust earthquakes that occurred approximately in the same area is significantly shorter than what would be expected from the widely accepted concepts of the seismic cycle. The article provides information on source parameters of the main shock, the operation of the Tsunami Warning Service, a catalog of aftershock mechanisms, the characteristics of strong ground motions caused by the main shock, and a brief description of the manifestation of a tsunami. A preliminary assessment of the macroseismic impact of the Kamchatka earthquake and its aftershocks revealed that the earthquake caused shaking of intensity 7–8 on the SIS-17 scale in Severo-Kurilsk and 6–7 in Petropavlovsk-Kamchatsky; no human casualties or serious damage caused by the earthquake and tsunami were recorded throughout the entire area of their propagation. Features of the source process development revealed by the results of the analysis of the diurnal variation of seismic energy released after the main event are discussed. The finite fault slip model of the earthquake based on the coseismic displacements from GNSS observations is presented.

Abstract Mutnovsky Volcano, ∼70 km SW of Petropavlovsk‐Kamchatsky, exhibits persistent degassing, hosts active hydrothermal springs and the Mutnovsky Geothermal Power Plant (MGPP) on its slopes. Using the network covariance matrix approach, we analyzed seismic data recorded in 2023–2024 by 15 seismic stations operating around Mutnovsky Volcano. We detected seismic tremor in the 1.5–5 Hz frequency range beginning on 6 February 2024, ∼10 days before a series of hydrothermal explosions occurred in the vicinity of the MGPP. The timing of these explosions was refined based on satellite imagery. Most of the tremor sources were located beneath the northeastern slope of the volcano at shallow depths. The spatiotemporal evolution of tremor activity, alongside independent volcanological data, suggest it was generated by magma‐hydrothermal processes activated by a magmatic fluid influx, which caused the hydrothermal explosions. Thus, observations of such seismic tremors may provide a short‐term precursor for future hydrothermal explosions.

The seismicity review of Kamchatka and surrounding territories for 2021 is given. In the Ka‑ mchatka earthquake catalogue, the minimum local magnitude of completeness is MLC =3.65, and for the Ka‑ mchatka seismically active region (φ=50.5–56.5°N, λ=156.5–167°E) MLC =3.05, and for earthquakes with h≥350 km under the Okhotsk sea MLC =3.65. The Kamchatka earthquake catalogue for 2021, published in the Appendix to this article, includes 1194 events with ML≥3.5 where the local magnitude is ML=0.5∙КS –0.75. 76 earthquakes with ML=3.6–6.55 were felt in Kamchatka and surrounding areas with seismic intensity I of 1–2 to 6 according to the Seismic Intensity Scale-2017 (Russian state standard). The level of seismicity according to the «SOUS’09» scale in 2021 corresponded to the «background average». For 34 events with ML≥5.0 that occurred in 2021 within the area of responsibility of Кamchatka Branch of Geophysical Survey RAS, an attempt to calculate the seismic moment tensor (SMT) was made. The strongest event for the year occurred on March 16 at 18h 38 m (ML=6.55, Mw=6.5) with an epicenter on the western slope of the Kuril‑Kamchatka deepwater trench, 80 km east of the Kronotsky Peninsula. The maximum concussions of I=5 points caused by this earthquake were recorded 140 km from the epicenter. In 2021, two new observation points were opened in the Kamchatka Territory.

The article studies the structure of the Earth’s crust and upper mantle of the Avacha Bay region of the Kamchatka Peninsula. One-dimensional sections of the dependence of seismic velocities on depth, obtained during the study are presented. These sections are constructed according to the data of the Petropavlovsk (PET), Dalniy (DAL), Institut (IVS), and Karymshina (KRM) stations for the period from 2000 to 2019. The stations are part of the permanent observational network of seismic stations of the Kamchatka Branch, Geophysical Survey, Russian Academy of Sciences. The sections are constructed to a depth of 300 km, which makes it possible to characterize the structure of the medium in the bay area, namely, to identify structural layers in the crust, the Moho boundary, and to estimate the degree of deviation of seismic wave velocities in the upper mantle from the corresponding values of the IASP91 global Earth model. The average values of velocities calculated from the obtained sections in the crust and upper mantle were significantly lower compared to the global model. The average deviation of the observed velocities from the model ones is 0.5–1.0 km/s in the crust, then it gradually decreases to a depth of about 180 km. At greater depths, the velocities in the obtained models coincide with the standard values. It should be noted that at the locations of the seismic stations, the lower boundary of the subducting Pacific Plate runs at depths of about 180 km. Therefore, the main reason for the difference in velocities is probably related to significant heating of material and the complex fluid-dynamic situation in the region of the mantle wedge.

The article presents instrumental and macroseismic data on the East Kronotsky earthquake of March 16, 2021, ML=6.6, Mw=6.5, discusses its tectonic position, duration and features of the aftershock process. As of the end of 2021, the earthquake is one of 15 shallow-focus (0≤h≤70 km) events with ML≥6.5 recorded in the Kamchatka seismofocal zone since the beginning of detailed seismological observations in Kamchatka in 1961. Focal mechanisms and moment magnitude values Mw of the East Kronotsky earthquake and its strongest aftershocks were obtained using the original method for calculating seismic moment tensors developed at the Kamchatka branch of Geophysical Survey RAS. The East Kronotsky earthquake did not cause casualties or destruction and was felt with an intensity I from 1–2 to 5 points on the SSI-17 scale in 17 settlements at a distance from the epicenter of Δ=141–386 km. The maximum intensity of tremors I=5 points was recorded at the Kronoki cordon of the Kronotsky State Nature Reserve (Δ=141 km). The magnitude of the East Kronotsky earthquake did not exceed the tsunamige‑ nicity threshold; no tsunami waves were observed on the coast of the Kamchatka Peninsula and adjacent territories.

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.

In this study, we investigated the crustal structure beneath the area of Central Kamchatka (Kamchatka Peninsula, Russian Far East) limited by latitudes 52.8 and 54.1 degrees. This area comprises parts of the active Eastern Volcanic Front and two mountain ridges Sredinny and Ganalsky, as well as several backarc volcanoes. We used the continuous data from the permanent stations and the temporary network installed in 2019-2020 to perform ambient noise tomography. We implemented a two-step tomographic inversion algorithm that initially generated the two-dimensional maps of group velocities for periods ranging from 1 s to 30 s, then found the optimal 1D model of shear wave velocities and derived the three-dimensional S-wave velocity distribution. In the resulting model, we observe a prominent low-velocity anomaly below the active volcanoes of Avacha and Koryaksky, which is traced to depths of similar to 40 km and may be associated with a zone of heated rocks suitable for petrothermal energy extraction. We propose that this anomaly represents a common magma pathway through the crust feeding both volcanoes. Beneath another active Zhupanovsky volcano, we observe three low-velocity layers at depths of 2 km, 8 km and 20 km indicative of a multilevel magma feeding system. We believe our findings will further the understanding of the complex processes occurring within these active volcanoes, which pose a tangible hazard to the relatively populated Petropavlovsk-Kamchatsky urban district. Beneath the Sredinny Ridge we reveal a high-velocity pattern at shallow depths, likely associated with consolidated magmatic structures. The low-velocity in the lower crust is interpreted as a high-temperature zone conserved here since the time when this area hosted an active volcanic arc. Upon further exploration, this high-temperature zone could prove to be a prospective source of geothermal energy. Below the Ganalsky Ridge, a prominent high-velocity anomaly extending to a depth of similar to 15 km can be attributed to the Precambrian to Carboniferous metamorphic rocks of predominantly mafic composition.

The seismicity review of Kamchatka and surrounding territories for 2020 is given. In the Kam chatka earthquake catalogue, the minimum local magnitude of completeness is MLmin=3.5, and for the Kamchatka seismically active region (=50.5–56.5° N, =156.5–167° E) MLmin=3.0, and for earthquakes with h≥350 km under the Okhotsk sea MLmin=4.1. The Kamchatka earthquake catalogue for 2020, published in the Appendix to this article, includes 1666 events with ML≥3.5; 94 earthquakes with ML=3.55–7.65 were felt in Kamchatka and sur rounding areas with seismic intensity I of 1–2 to 6–7 according to the Seismic Intensity Scale-2017 (Russian state standard). For 49 events with ML≥5.0 that occurred in 2020 within the area of responsibility of Кamchatka branch of Geophysical Survey RAS, an attempt to calculate the seismic moment tensor (SMT) was made. The level of seismicity according to the "SOUS'09" scale in 2020 corresponded to the “high”. On March 25, 2020, there was a strong earthquake with Mw=7.4, named “the Paramushirskoe earthquake”. The earthquake was accompanied by a large number of aftershocks.

The article presents data on the types of observations and information resources of the Kamchatka Branch of the Geophysical Survey of the Russian Academy of Sciences (as of 2022), which can be used by scientific and educational organizations of the Russian Federation for studying precursors and developing methods for predicting earthquakes and volcanic eruptions, solving a wide range of research tasks in the field of geophysical monitoring of seismically active areas and others. Information resources and observation data are illustrated on the example of the Unified Information System of Seismological Data of the KB GS RAS and time series data of meteorological, hydrogeological observations and observations of volumetric radon activity in the soil gas at the Moroznaya station.

Iturup is the largest island of the Kuril Arc with more than 20 Holocene volcanoes of which 9 considered active. Here we investigate the central part of the island where we deployed in 2022-2023 a portable network of 12 seismic stations. The data of this network together with several permanent stations in surrounding islands were used to identify almost 300 events and to perform seismic tomography based on the picked arrival times of the P and S seismic waves. A challenging problem was that most of the events were located outside the network, and we performed careful analysis to examine the actual capacity of inversion with such data to recover seismic velocity structures below the network. In the resulting model, we found a dominating high-velocity anomaly below the central part of the study area, which is bounded by zones of low velocities and high Vp/Vs ratio collocated with two active volcano complexes (Chirip to the north and Ivan Grozny to the south). Below the third volcano, Baransky, we observe a change of the Vp/Vs ratio from high at large depths to low at shallow depth, indicating the process of degassing, which is supported by strong fumarolic activity and hydrothermal manifestations around this volcano. At depths of more than 20 km, the feeding paths from Baransky and Ivan Grozny volcanoes seem to be connected in one anomaly representing a common magma source below the center of the island. This seems to be a common feature observed below several volcanic islands, such as Tenerife and El Hierro, where the high-velocity rigid core in a central part is surrounded by low-velocity flows associated with recent volcanic manifestations.

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 mechanisms of preparation and occurrence of the strongest deep-focus earthquakes with MW≥8, as well as their surface manifestations, remain insufficiently studied because of the lack of the relevant data. There are but three seismic events of this kind which have so far been instrumentally recorded. This paper describes the identification and analysis of the changes in the characteristics of modern crustal movement of the 2013, MW 8.3 Sea of Okhotsk deep-focus earthquake based on the data from long-term continuous geodetic-class GNSS stations in the Sea of Okhotsk region on the Kamchatka Peninsula, the Sakhalin Island, and the coast of the Sea of Okhotsk and the Sea of Japan. There has been found temporal stability of variations in the average annual geodetic site velocities. The coordinates of GNSS-stations do not show non-linear changes typical of strong shallow earthquakes in the initial post-seismic period. The Maxwell rheology for modeling of viscoelastic relaxation of the asthenosphere/upper mantle as a result of seismic impact allows for a first approximation to qualitatively and quantitatively reproduce the displacement patterns of GNSS-sites of the Kamchatka Peninsula observed in the initial postseismic period (2–3 years after the mainshock). After that, the model estimates of postseismic movements of the peninsula become systematically lower than the observed. The values calculated for the OKHT station motion on the western coast of the Sea of Okhotsk are in good agreement with those recorded for postseismic displacements over the entire measurement interval. The observed directions of the Sakhalin Island postseismic movements systematically deviate to the northeast from the model directions and are oriented almost orthogonally to the Kuril-Kamchatka Trench. Besides the viscoelastic relaxation process, another possible reason for this issue could be an enhanced viscous friction in the bottom of the subducting Pacific plate, leading to the intense deformation of the Sakhalin Island and the western coast of Kamchatka.

The seismicity review of Kamchatka and surrounding territories for 2018–2019 is given. In the Kamchatka earthquake catalogue, the minimum local magnitude of completeness is MLmin=3.8, and for the Kamchatka seismically active region (latitude = 50.5–56.5° N, longitude = 156.5–167° E) MLmin=3.7, and for earthquakes with h≥350 km under the Okhotsk sea MLmin=3.8. The Kamchatka earthquake catalogue for 2018–2019, published in the Appendix to this article, includes 3646 events with ML≥3.5; 228 earthquakes with ML=3.65–7.3 were felt in Kamchatka and surrounding areas with seismic intensity I of 1–2 to 6–7 according to the Seismic Intensity Scale-2017 (Russian state standard). For 134 events with ML≥5.0 that occurred in 2018–2019 within the area of responsibility of Кamchatka branch of Geophysical Survey RAS, an attempt to calculate the seismic moment tensor (SMT) was made. The SMT and depth h of the equivalent point source were calculated for 67 earthquakes in 2018 with a range of ML=5.0–7.3, and for 67 events in 2019 with a range of ML=5.0–6.45. The level of seismicity according to the "SOUS'09" scale in 2018 corresponded to the “background increased”, but within the assessment accuracy – “high”; for 2019 it was the “background average”. On December 20, 2018, there was a strong earthquake with Mw=7.3, named “the Angular Uplift earthquake”. This earthquake was the strongest intraplate event, which belongs to the region south of the junction zone of the Kamchatka and Aleutian trenches The earthquake was accompanied by a large number of aftershocks.

Avacha and Koryaksky are active volcanoes located in the vicinity of Petropavlovsk-Kamchatsky, the main city of Kamchatka, and they represent a serious hazard to the surrounding population and infrastructure. Here we investigate the upper-crustal structure beneath these volcanoes by implementing local earthquake tomography based on data from permanent seismic stations and from a temporary network installed in 2018–2019. Although the total amount of seismic rays recorded by the temporary network dataset is much lower, adding this data and attributing an appropriate weight lead to considerable increase of the resolution compared to the case of using merely the permanent network data. The resulting distributions of the P and S wave velocities, and especially the Vp/Vs ratio, reveal two magma reservoirs located below Avacha and Koryaksky volcanoes. Different depths of their upper limits explain differences in the eruption activity styles of these volcanoes. Below the Avacha Pass, we observe a thick layer of low-velocity soft volcaniclastic sediments formed due to the activity of both volcanoes. A conservative numerical estimate of a steady-state conductive temperature field around the magma source below Avacha demonstrates that the high temperature zone can be reached by drilling a well to a reasonable depth, thus suggesting that the area might be exploited as a source of geothermal energy.

The area of Central Kamchatka limited by latitudes of 52.5 and 54 degrees includes six active volcanoes (Avacha, Koryaksky, Zhupanovsky, Mutnovsky, Gorely and Opala), as well as a number of dormant and extinct strato-volcanoes, monogenic cones and large calderas. Furthermore, it contains the Malko-Petropavlovsk fracture zone (MPZ), which marks the boundary between two distinct subduction regimes to the south and to the north. We present a new seismic tomography model for this area, which was constructed based on the joint use of data of the Kamchatkan permanent seismic stations and a temporary network installed in the region in 2019-2020. A series of synthetic tests have demonstrated fair resolution of the derived seismic velocity structures in the crust and in the mantle wedge down to-150 km. The distributions of the P and S wave velocities, and especially the Vp/Vs ratio, clearly highlight the connection between the volcanic centers in Central Kamchatka and the sub -ducting slab. At depths below 40 km depth, we observe two large low-velocity anomalies centered below Zhupanovsky and Mutnovsky volcanoes and covering all other volcanoes in the area. In the vertical sections, the corresponding anomalies of high Vp/Vs ratio have mushroom shapes with the heads spreading along the bottom of the crust, which probably represent the underplating of magma material that feeds the volcanoes of the groups. The tomography results also reveal some important tectonic features, such as a V-shaped fault system in the Avacha Graben, which is the part of the MPZ.

Estimation of the influence of anthropogenic factors on the seismic signal is an important problem in ensuring the quality of seismological data and, accordingly, the quality of scientific research. Due to the unprecedented situation associated with the introduction of measures to prevent the spread of COVID-19, non-working days were established in Russia from April 4 to April 30, 2020. It became possible to assess the impact of a notable decrease in anthropogenic activity on the seismic signal (noise) recorded by seismic instruments in the territory of the largest city of the Kamchatka, Petropavlovsk-Kamchatsky. We study seismic noise by standard technique, based on the analysis of the probability density function of the noise power spectral density obtained from the data of the digital archive of the noise spectra of seismic stations. A decrease in the seismic noise power level below the minimum values of the same periods of previous years was registered at stations installed in schools, residential buildings (boarding schools) or near public and office buildings. The minimal anthropogenic influence stations were selected. The obtained data can be used for determination the features of the work of both stations and individual channels, taking into account their direction and position, relative to the objects of human activity.

We have carried out a preliminary study of the relationship between local seismicity and the behavior of atmospheric temperature and humidity based on data from the local seismic catalog and archival data from the Karimshina observatory in Kamchatka. The chemical potential of water vapor molecules contained in the surface layer of the atmosphere was used as a measure of the impact of seismic processes on the atmosphere. Following the accepted terminology, we call it the atmospheric chemical potential (ACP), which is calculated from the air temperature and humidity. ACP supposedly increases in the process of air ionization by radon (Rn) which is released during the enhancement of seismic activity. It is assumed that Rn rises to the surface more intensively along seismic faults or volcanic fumaroles. Air ionization leads to a decrease in the air humidity and an increase in its temperature, and eventually results in an increase of ACP. We have subtracted the 30-day moving average of the ACP from its time variations to better reveal the ionization contribution. Thus, intervals of increased ACP were found in the temporal vicinity of earthquakes. The duration of these intervals ranged from a week to a month or more. The maximum response of the atmosphere to deep earthquakes is weaker and shifts closer to and beyond the date of a seismic event. The effect was more evident when the wind was directed from an expected Rn release region towards the observatory. We have not found a relationship between the magnitude of earthquakes and the magnitude of the ACP response. The reliability of these conclusions as well as the possibility of using the meteorological methods for earthquake prediction will be further examined.

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.