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.

CHINGIZ EARTHQUAKE on January 20, 2015, KR=12.2, mb=5.6, I_0^P=5–6 NEAR the SEMIPALATINSK POLYGON (Eastern Kazakhstan)

The work presents the results of data analysis of the earthquake on January 20, 2015, mb=5.6 occurred at the low-active region of Eastern Kazakhstan near the border of the former Semipalatinsk Test Site. The work briefly describes the seismicity of the Semipalatinsk Test Site related to aseismic regions according to the acting map of general seismic zoning. The earthquake was recorded by permanent seismic stations of the Institute of Geophysical Research of the Ministry of Energy of the Republic of Kazakhstan and by two strong-motion accelerometers. The earthquake was felt at distances up to 300 km from the epicentre, its maximum intensity was noted at Medeu settlement where the shaking intensity was 56 by the MSK-64 scale. The earthquake focal mechanism is shown, the parameters of seismic effects and response spectra are calculated.

Assessment of social aspects of seismic hazard

This paper is intended to illustrate the applicability of the results obtained from the investigations of social aspects of seismic hazard of the Russian Federation (RF) through the example of the high-seismicity region – the Far Eastern Federal District (FED). Within the FED the comparison of the areas of various seismic zones as per regulatory maps of General Seismic Zoning dated 2016 (GSZ-2016) has been performed and population estimates for each zone have been obtained. For the first time population estimates for zones with increased seismic hazard – grades A, B and C as per GSZ-2016 – are provided. The data obtained may be used for the evaluation of additional risks for FED’s population.

Increasing Resolution of Seismic Hazard Mapping on the Example of the North of Middle Russian Highland

The standard problem of engineering geophysics, solved for road and house building and other construction types, is in the localization of areas with increased mobility in the upper part of a geological cross-section and in the parameterization of this mobility in terms of seismic intensity. There is a standard approach, according to which researchers assess the elastic strength characteristics of the core to a depth of about 30 m, implement the accumulation of seismogram observations, simulate accelerograms for particular conditions and, taking into account the data of complex geophysical methods, calculate the increment of seismic intensity as one of the parameters of a seismic hazard. The final result of this approach has the form of a seismogenic hazard map and a set of recommendations including the consideration of identified areas with a significant increasing seismic intensity increment, due to the peculiarities of the geological structure of polygons. This result is reliable, but very expensive, and requires the development of primary estimations of the rock massif with reduced resistance to external loads, which would optimize the efforts in engineering drilling and in field geophysical measurements in order to densify their spatial grid in the vicinity of a priori known positions with an increased seismogenic hazard. In addition, relatively sparse grids of wells, as well as local geophysical profiles laid under conditions of a complicated landscape, do not accurately localize risky areas in order to focus the attention of builders on strengthening the specific part of raised constructions. Following the wishes of our customers and relying on long-term testing of our interpretational developments, we formed an approach to primary hazard forecasting based on remote sensing data and digital elevation models, which can be classified as data with relatively free access. This article presents the results of research which was based on these free-of-charge data and which was developed in the field of construction of ground engineering structures for agricultural purposes, where one of the factors of mobility in the upper part of a cross-section is intensive karstification. Basically, the construction area according to the general seismic zoning maps is seismologically passive, though the relatively fast dynamics of karst determines the relevance of the detailed seismic zoning. The results of our interpretations are verified by deep geological and structural reconstructions based on wave analogies. The representativeness of the final forecast was confirmed by subsequent seismic assessments, which is related to the scientific novelty of the presented article. The authors’ technology for the qualitative and quantitative interpretation of remote sensing data and digital elevation models with high resolution provides the opportunity to increase the spatial resolution of seismic microzonation forecasts, implemented by standard geophysical methods, and it determines the practical significance of completed research.

Seismic hazard assessment for the underwater gas pipeline route in the water area of the Nevelskoy Strait

The presence of seismic threat multiplies the environmental hazard, especially for oil and gas production and transport facilities in water areas. Currently, there are no normative maps of general seismic zoning of the water areas of the inland and marginal seas of Russia, especially since there are practically no maps of detailed seismic zoning and seismic microzoning of even individual parts of the water areas. Taking into account the fact that intensive development of offshore oil and gas fields and the Northern Sea Route has begun, the development of such maps becomes a very urgent scientific and practical task. The seismic hazard assessment for the submerged crossing was carried out in 2008. The initial seismic effects were calculated using a probabilistic seismic hazard analysis based on five models of seismic zones and three types of models of attenuation of peak and spectral accelerations. The results of the performed calculations, including deaggregation, have shown that the initial seismicity of the area of the gas pipeline crossing route through the Nevelskoy Strait for a return period of 1,000 years is lower than indicated on the OSR-2016-B map, where the eastern end of the crossing route through the strait is characterized by the initial seismicity equal to 9 points. The soil conditions (seismic microzoning) have been taken into account by three different methods: the seismic rigidity method, the calculation method, and the method considering the thickness of Quaternary deposits. The present studies show that seismic effects vary along the pipeline route from the mainland to Sakhalin Island from 8.4 to 8.9 on the MSK-64 scale for the recurrence period of seismic shaking T = 1,000 years and from 9.3 to 9.7 points for T = 5,000 years.

Variations in the integral amplification of of seismic ground motions on the territory of Kiev

The relevance of the research and the results presented in the article is due to the need to provide the designers of seismic-resistant construction with maps of seismic zoning of settlements and agglomerations on the territory of Ukraine in the amplitude parameters of seismic ground motions. An analytical-empirical approach to mapping is proposed on the example of the territory of Kyiv, which can be implemented in conditions of an insufficient number of results of instrumental seismological observations. This approach gives positive results provided that the territory is well studied in geological terms. Within the territory of Kyiv, using the method of seismic-geological analogies, areas (taxonometric zones) have been identified that are homogeneous in response to seismic effects. For all taxonometric zones, seismic-geological models of the soil strata were built and their spectral characteristics were calculated taking into account the nonlinear deformation of the soil. The averaged frequency response was also calculated for the ground conditions of the territory of Kyiv as a function of the distribution of the average values of the spectral amplification of seismic oscillations in frequency for all zones. A map of the distribution of the deviation of the integral amplification of seismic vibrations from the average value for the territory of Kyiv was constructed. It is proposed to use a spectral amplification map to determine the values of the calculated relative ground acceleration of the investigated site when using the spectral method for calculating the emergency combination of loads taking into account the seismic effect. The map of the distribution of the deviation of the integral amplification of seismic oscillations from the average value for the territory of Kyiv is an intermediate stage in the construction of seismic zoning maps for Kyiv in amplitude terms of ground motions.

On the question of setting the level of calculated impact and reliability of high-rise construction

The question of setting the seismic design input on high rise buildings is considered. The existing approaches to accounting for increased responsibility of high rise buildings in Russia are described. The proposal to reduce the probability of an acceptable building failure in proportion to the number of floors and Guideline proposals to increase the reliability factor and using maps of general seismic zoning are analyzed. The main disadvantages of methods described are indicated. It is shown that the current regulatory documents in the field of earthquake engineering do not provide the same reliability of designed structures in general and high-rise buildings in particular. The influence of seismic dangers in according with seismic zoning maps on the reliability of the designed objects is noted. An approach to generating the design input based on the permissible probability of its exceeding is considered using the example of five five-storey buildings and one 25-storey buildings. The probability of the admissible damage value included in the normative calculations is estimated. An estimate of the allowable failure probability on the value of acceptable damage (risk) is proposed under the assumption of a normal distribution of damage caused by earthquake. It is shown that the allowable failure probability decreases with decreasing acceptable damage only in the area of small damages. An approach to the assignment of seismic action based on an assessment of seismic risk has been formulated. The system of design coefficients used to calculate seismic loads on high-rise buildings is analyzed. It is noted that along with an increase in the design level of seismic acceleration, it is necessary to increase the coefficient, taking into account the low damping of high-rise buildings oscillations. At the same time, it is possible to significantly reduce the reduction coefficient by regulating the strains between the building floors.