IEPT RAS

The scientists from the Netherlands, Russia, and Romania estimate earthquake source parameters in Vrancea seismic zone and surrounding regions between 2014 and 2020, and determine the stress field via focal mechanism inversion and unsupervised machine learning. The work was published in Tectonophysics (Q1, JIF=3.048).

Major earthquakes of M ≥7 are complex. Seismic energy accumulation, release, and redistribution in the lithosphere are not yet well studied. The geometry, timing, and slip distribution of the complex nonlinear system of the lithospheric blocks-and-faults involved is usually not well resolved.

During last decades, the question of the effect of ocean tides on seismicity has been widely investigated. The issue of whether tidal forces really affect seismicity has been raised many times in the literature.

In the present study the differential probability gain approach (Shebalin et al., 2012; Shebalin et al., 2014) is used to estimate quantitatively the change in aftershock rate at various levels of ocean tides, relative to an average Omori-Utsu model that supposes no dependence on tides. The differential probability gain function is a numeric factor indicating how much the rate of aftershocks is increased or decreased on average at specific values of the tide heights.

Man-made seismicity is a response of the brittle crust to fluid injection at depth and to the subsequent increase in pore-pressure and stress field perturbations. In Oklahoma, where the sharp increase in earthquake rate correlates with injection operations, we show that the earthquake-size distribution can differ significantly on the volume of injected fluid. The size distribution of M<3.5 earthquakes exhibits a near-constant slope b, while significant variation of b-values (from b≈1to b>2) may be documented for larger magnitude ranges. This change shows statistically significant positive dependence on injection activity. In addition, largest events occur at the border of the injection area at some distance from massive injection, and in the periods of steady injection rate. These observations suggest that a deficit of large induced earthquakes under conditions of high injection rate can be accompanied by an overall increase of natural seismicity along pre-existing faults in the surrounding volume, where large events are more likely to be triggered over longer space-time scales.

More“Condition of occurrence of large man-made earthquakes in the zone of oil production, Oklahoma”

Rapakivi in Finnish means «rotten stone». These very beautiful granites, widely used in construction as facing material, are often represented in nature by granular-block-destroyed massifs, and often destruction is observed only in the near-surface region. Over time, architectural structures made from rapakivi also tend to crack and collapse. Among other things, there is the problem of preventing the destruction of the unique Alexandria Pillar on the Palace Square in St. Petersburg. Failure of rapakivi granites is usually interpreted as fatigue failure, generated, for example, by cyclic changes in internal stresses during heating and cooling of rocks and during their freezing and thawing.

In the journal “Zeitschrift für angewandte Mathematik und Physik” (WoS, Scopus, Q1) publishedby Springer, the article“A boundary value problem in the theory of elasticity for a rectangle: exact solutions” was published. Among the authorsareemployees of IEPT RAS: Leading Researcher, D.Sc. (Phys.-Math.) M.D. Kovalenko, Senior Researcher, Cand. Sc. (Phys.-Math.) I.V. MenshovaandSenior Researcher, Cand. Sc. (Phys.-Math.) A.P. Kerzhaev.

In the article, we derive the formulas that describe the exact solution of the boundary value problem in the theory of elasticity for a rectangle in which two opposite (horizontal) sides are free and stresses are specified (all cases of symmetry relative to the central axes) on the other two sides (rectangle ends). The formulas for a half-strip are also given. The solutions are represented as series in Papkovich–Fadle eigenfunctions whose coefficients are determined from simple formulas.

The research was funded by RFBR and NSFC according to the research project No. 20-51-53021 and the Russian Science Foundation under grant No. 19-71-00094.

Seismotectonic processes of the Shillong Plateau (SP) have been influenced by the Himalayan orogeny, the India-Burmese subduction, and the Bengal Basin evolution leading to high seismic activity in the region. A probabilistic assessment of the seismic hazard of the SP was carried out in order to provide scientific information to the engineering and disaster risk management communities. Seismic hazard analysis is used to determine ground fluctuations in densely populated areas of the SP and, in particular, in the cities of Shillong, Nongpoh and Tura. This analysis is based on the use of historical and instrumentally recorded regional earthquakes since 1411 and deals with uncertainties related to earthquake magnitudes, rupture locations, and the frequency of ground motion exceedance.