Results and prospects of seismological observations in the central part of the Baikal rift

This article reports the results of detailed seismological observations in the Central Baikal region conducted by the local network of seismological stations of the Buryat Division of the Geophysical Survey of the Russian Academy of Sciences. The local network was created in the 1990s. A crucial feature of the network is the combination of seismic monitoring both in the passive mode (the study of natural seismicity) and in the active mode, with a controlled vibration source of seismic waves. The study area covers the Lake Baikal region and adjacent territories characterized by high seismic activity. Here occurred several catastrophic earthquakes including the strongest one during the period of instrumental observations – the Middle Baikal’1959 earthquake. Recently here occurred the Kudarinsky earthquake on December 9, 2020 with mb=5.4. For more than twenty years the network of observations has been expanding, the equipment has been upgrading. A significant amount of seismo-logical material has been accumulated. Broadband data was processed by the receiver function method. The Moho and the lithosphere-asthenosphere boundaries for stations of the network are determined. Shear seismic wave attenuation characteristics are obtained and the possibility of energy classification of Baikal earthquakes by coda-waves total oscillations is shown.

Results of fundamental and applied seismological research in the Magadan region in 2016-2020

The results of fundamental and applied research, carried out by Magadan Branch of GS RAS during 2016-2020 in Magadan and Chukotka regions are presenting. Estimation of Seismic hazard of Russia’s Northeast (Magadan region) and seismic hazard maps for recurrence periods of 500, 1000 and 5000 years in scale close to that of detailed seismic zoning (DSZ) were made in cooperation with Institute of the Earth’s Physics RAS. In course of this work the estimation of initial seismic intensity and parameters of possible ground shaking in areas of critical facilities of Magadan region were made. For all of them a seismic micro zonation was carried out with methods of direct earthquake registration and comparing acoustic impedance. As result, a seismic amplification and intensity of seismic impact on the soils under main critical facilities were obtaining. The research results are shown on detailed seismic zoning maps that are basic for building projects of objects above.

Creepex-analysis of processes in focal zones of large earthquakes by means of GIS-ENDDB

The creepex (creep & explosion) parameter provides information on the relation between low- and high-frequency radiation components in the earthquake source and has become a physically meaningful tool for analyzing various aspects of seismogenesis, in particular, the diagnostics of the preparation processes and the its aftershocks activity of a strong event. This paper investigates the spatial-temporal dynamics of creepex in the focal zones of a number of the major earthquakes from the plate convergence regions, including continental Kashmir earthquake (08.10.2005, MS=7.6) and continental-oceanic Tohoku (11.03.2011, Mw=8.7). One of the goals of this work is to demonstrate the capabilities of the method in studying physically grounded patterns of focal zones development at the first hours after the main shock. Because of this study, the following regularities of the source relaxation process were revealed: the partiality of the aftershock process, positive values of the creepex at its first hours (explained by the influence of the dilatancy process), and abrupt changes in the creepex during deep transitions (explained by the thermodynamic effect and by the increase in pressure with depth).

Features of time variations of microseismic noise at seismic stations in Tajikistan

The spectral structure of microseismic noise in the frequency range of 0.01-40 Hz at different times of the day and year, recorded by broadband equipment at eight IRIS group seismic stations in Tajikistan in 2005-2020, was analyzed. Two disjoint frequency ranges are distinguished, which we conditionally call "high-frequency" (2-40 Hz) and "low-frequency" (0.01-0.75 Hz) noise, separated by a natural drop in the noise amplitude to 20-30 Db. It is assumed that the high-frequency range of noise has a local nature, due to exogenous sources of natural origin in the form of wind gusts, concussions from powerful watercourses and fluctuations in the level of large reservoirs, as well as man-made in-terference due to road and quarry explosions, the work of large industrial enterprises and concussions from road traffic. Low-frequency noise is most likely caused by global storm microseisms. High-frequency noise has a well-defined daily frequency, which is completely absent in low-frequency noise. At the same time, in both frequency ranges, the existence of a clearly pronounced seasonal peri-odicity has been established, the amplitude of which reaches 6-7 Db for high-frequency noise and about half as much for low-frequency noise. However, at the same time, the seasonal frequency of high frequency and low-frequency noise turns out to be antiphase, which indicates in favor of the different genesis of these two components of microseismic noise. The amplitude of the diurnal periodicity in variations of the high-frequency noise level is maximal during the daytime, remaining approximately constant for 8-10 hours. At the same time, the decline in the noise amplitude in the evening lasts longer than the steeper morning growth. The time intervals of a sharp increase and decrease in the intensity of the discussed daily extreme are quite well correlated, respectively, with morning and evening twilight at different times of the year. This is reflected in the wider flat part of the maximum noise level in summer compared to winter and the differences in its level up to 6 Db in favor of summer time. This observation can be considered as a manifestation of the deep influence of the Sun on the oscillatory processes that generate high-frequency microseismic noise.

The unified system for storing and accessing geophysical data. Traditions and new approaches

The features of the development of data collection systems within the Information Processing Center (IPC) of the Geophysical Survey of the Russian Academy of Sciences (GS RAS) are presenting. Historical information is given, including technical details related to the systematization of the archive and the evolution of geophysical data formats. The historical, territorial features, as well as the experience of deploying such information systems within the Federal Research Center of the Unified State Social Service of the Russian Academy of Sciences and abroad are taken into account. A new concept of building an information system is proposed, which takes into account the requirements for scalability, reproducibility at various objects and the use of standard software. A lot of work was done to form a homogeneous archive of waveforms and an inventory of metadata for seismic stations, which resulted in the possibility of including the GS RAS in the international centers for processing geophysical information based on FDSN. Creation of a distributed collection and processing system using a cloud service allows abstracting from the territorial features of collecting and storing geophysical information, which increases the performance of the data access service and the degree of technical readiness of key system nodes.

Digital seismic logger "Ermak-5". Five years of development

The published data on several well-known seismic recorders used in modern seismological moni-toring systems are considered, and their qualitative comparative analysis is carried out. Infor-mation about the presence of Russian devices of this class in the State Register of measuring in-struments is given. The key technical characteristics of the "Ermak" recorder and confirming the results of laboratory and field experiments are given. At the same time, special attention is paid to the correspondence of the amplitude-frequency characteristics of the recorder to the reference analogs. A brief description of the flexible power management system for the recorder modules, which is designed to reduce power consumption, is given. The minimum value of the power con-sumption is about 300 mW when recording through six channels, which makes it possible to ef-fectively use the device for long-term measurements using autonomous power supplies. The in-ternal clock of the recorder is synchronized using GPS/GLONASS systems (hundreds of nano-seconds) and NTP-services (tens of microseconds). The efficiency of operation is ensured by the presence of a LCD-screen at the logger, on which, in addition to time and parametric information, waveforms are displayed in various display modes. There is also a list of facilities where "Ermak" was tested or is currently being operated.

On the stability of the seismic mode parameters in time by the example of the east of the central part of Northern Caucasus

The parameters of the seismic regime of the eastern zone of the Central Caucasus are deter-mined based on the new catalog data. A similar study is being carried out for the third time: in 1996, 2015 and 2021. The basis for work in the area surrounding Grozny was laid in 1996 by a comprehensive study of geological, geomorphological, geophysical and seismological ma-terials. When comparing the results, the stability of the seismic regime parameters was estab-lished: the repetition schedule b and seismic activity A3.3 near Grozny, the capital of the Che-chen Republic and a large industrial center in 2015 and 2021. In both cases, the estimates were performed on the same the same territory bounded by coordinates: 41.1-45.6N and 42.6-48.8E. The same basic earthquake catalog was used for the calculations. The difference was in the number of events that took place in this territory from 2015 to 2020 inclusive.

Ring-shaped seismicity structures, being formed in the Alaska region: Justi-fied prediction of the place and magnitude of the Simeonof earthquake of July 22, 2020 (Mw 7.8)

We have been studying some seismicity characteristics connected with Simeonof earthquake of July 22, 2020 (Mw 7.8) in the area of Shumagin seismic gap, located in the region of South Alaska. 8 years before this event, the authors picked up here ring-shaped seismicity structure. Using characteristics of this structure we made a conclusion on preparation for large earth-quake (Mw~8), similarly to many events in subduction zones. We used data on threshold magnitude and size of the ring structure, and earlier obtained dependences of these parame-ters on magnitudes of main events for the subduction zones in the Eastern Pacific. Accumula-tion of new seismicity data prior to 2020/07/22 allowed us to specify the source location and magnitude of the Simeonof earthquake: Mw=7.9±0.3. It was shown that after this event new ring structures continued to form, which can correspond to preparation for larger earthquake: Mw=8.2±0.2. Geodynamical processes, which lead to formation of the ring structures, are discussing.

Kamchatka seismic monitoring and Earthquake prediction system and its evolution. Main results of observations in 2016-2020

In this paper we present brief review of results of Kamchatka Seismic Monitoring and Earthquake Prediction System operations in the last five years. In addition, the retrospective of development of hardware, equipment and software of the System performed. The main direction in the System evolution in this period concerned the creation and modernization of data acquiring and pro-cessing methods. One of main results is creation basic informational space, that includes all pro-cesses if seismic observations, from data acquiring till exchange (including external users) of da-ta processing results. In particular, the system of data storage was deeply modernized, high-speed access to the data archive was provides, high-performance computing clusters were deployed, all seismic stations were combined in the unified network. Development algorithms and software for data processing and seismic regime controlling was continued. Creation and development of the Seismological Data Informational System (SDIS) provide the access to seismic observations re-sults for research community. The service of automatic data exchange with external users was created and incorporated in SDIS. Kamchatka Seismic Monitoring and Earthquake Prediction System in 2016-2020 allowed registering and processing over 83 thousand tectonic and volcanic earthquakes. The complex studies for seven the strongest ones were conducted. Detailed analysis showed, that magnitude of completeness for regional scale is MLc=2.5, and for local scale (for example – volcano seismic monitoring) – MLc=–0.2.

Global earthquakes in the 2021 first half according to the GS RAS

Data on the 2021 first half Earth seismicity at the level of strong earthquakes with magni-tudes mb6.0 according to the Alert Service of the Geophysical Survey RAS are given. The review also includes information on 81 earthquakes in Russia and adjacent territories, felt in the settlements of the Russian Federation. For 14 strong earthquakes, within one or two days after their occurrence, Informational messages were published, and information about the focal mechanisms was giving. The strongest earthquake of the Earth with MS=7.8 (Mw=8.1) occurred on March 4 at the Kermadec Islands, New Zealand. The largest human casualties and material damage during the study period were caused by catastrophic earth-quakes with MS=5.1 (Mw=5.8) and MS=5.9 (Mw=6.3), which occurred on January 14 at the Sulawesi Island, Indonesia. As a result of the earthquakes, 81 people died, 826 were injured. The strongest earthquake in Russia was the March 16 earthquake with MS=6.7 (Mw=6.6) off the eastern coast of Kamchatka. The maximum shaking intensity in Russia (I=6) was manifested by the strong Khuvsgul earthquake with MS=7.2 (Mw=6.8), which took place on January 11 in the Northern Mongolia, near the border with Russia. The position of the main shock and its aftershocks indicate the intensification of the seismic process in the north-western part of the Khuvsgul rift zone. According to the focal mechanisms of the main shock and two strong aftershocks, the stress of the northwest/southeast extension prevails in this zone, and the predominant slip type along the faults of the northeast strike is a nor-mal fault. The global seismic energy released in the 2021 first half remains, as in the previ-ous two years, at a reduced level, relative to the average for the last 11.5 years, which indi-cates a continuing seismic calm.