Izvestiya, Physics of the Solid Earth最新文献

An algorithm for optimizing the trajectories and movement sequence of a fleet of marine seismic survey vessels in solving the problem of marine seismic surveys using bottom stations is presented. The algorithm is based on solving the traveling salesman problem with mixed deliveries and collections of goods (TSPDC). A description of the algorithm extension to a problem that takes into account static closed zones that simulate ice and meteorological conditions unsuitable for the ship movement is given. The Dubins path algorithm provides a path close to the minimum and takes into account real characteristics of the ship movement and its speed when performing various types of work (installing bottom stations, collecting stations, maneuvering, etc.). The scientific novelty of the study lies in applying the solution of the TSPDC to problems of marine geophysics with the condition of presence of closed zones and developing an algorithm for optimizing the work of seismic vessels with the use of bottom stations, which is relevant in the conditions of the Arctic shelf during the period of limited navigation. The algorithm described in the article makes it possible to take into account the return of the vessel for collecting the equipment when working with bottom stations in the transition zone. The developed algorithm for planning marine seismic surveys formed the basis of the application software. The formalization of the problem, the results of the algorithm operation, and examples of planning on test data are presented. The possible limitations for the proposed algorithm are raised. The obtained results are applicable for further use in the implementation of tasks on optimizing the work plan for marine seismic surveys with several vessels, both when planning seismic surveys and when adjusting plans directly on the ship. The use is also justified if it is necessary to reenter the profile (for example, when reworking out a defective work area).

In this paper, we present the first results of complex geological and geophysical studies of active tectonics in the northeast of Taymyr that were carried out during the expedition of the Northern Fleet and the Russian Geographical Society in 2020. At the foot of the Byrranga Mountains, a wide zone of active fault-folded tectonic deformations was identified and studied. The general kinematics of displacements is reverse-thrust with signs of shear. The structural style of young tectonic deformations bears a direct resemblance to well-studied structural analogues of the Central Asian seismic belt. The Taymyr seismotectonic zone reveals both spatial and genetic isolation. It has an individual model of the Late Cenozoic geodynamic evolution and modern seismotectonic regime, which differs sharply from the Laptev Sea rift zone adjacent to the east. A complex of geological and geophysical methods showed the high efficiency of application in the Arctic to identify young fault-fold structures, which are potential sources of strong earthquakes.

During the East Anatolian earthquake with M_w = 7.8, which occurred on February 6, 2023 at 1:17 UTC, the 361 km long segment of the NE-trending East Anatolian active left-lateral fault zone (EAFZ) was activated. A left-lateral displacement took place at a distance of 318 km on formed seismic ruptures. Its maximum magnitude of 8.5 m is registered northward of the earthquake epicenter. To the northeast, the displacement of several meters is maintained over a significant length of the activated segment and is accompanied by uplift of the south-eastern side of the ruptured zone at up to 1.5 m. To the southwest of the maximum displacement area, the strike slip decreases from it at shorter distances compared to the northeastern part and the vertical component varies, although the southeastern side is mostly uplifted. In the terminal southwest, the strike slip is replaced by normal faults, gaping fractures, and other manifestations of transverse extension, which are accompanied by landslides and are mainly secondary seismic dislocations. Left lateral slip also occurred at the northern ends of the western and eastern branches of the Dead Sea Transform (DST), adjacent to the EAFZ from the south. Despite the fact that the energy distribution of numerous aftershocks along the EAFZ is generally proportional to the distribution of offsets on seismic ruptures, the slip on the EAFZ occurred during and immediately after the main shock. In the northern part of the DST, a significant decrease in the amount of energy released by strong earthquakes during the last centuries has been established. We consider that the tectonic stress accumulated in the northern part of the DST became the important geodynamic source of the East Anatolian 02.06.2023 earthquake.

Based on the amplitude spectra of surface waves, the source parameters of the strong Turkish earthquakes on February 6, 2023 (M_w = 7.8 and M_w = 7.7) were calculated in two approximations: an instantaneous point source and an elliptical shear dislocation. As a result, fault planes were identified, data were obtained on the scalar seismic moment, moment magnitude, focal mechanism, and source depth of the considered seismic events, and the integral parameters characterizing the fault geometry and its development in time were estimated. It is shown that the sources of the earthquakes under study were formed under the action of the regional stress field and their focal mechanisms were sinistral strike-slips with a strike direction close to the strike of the East Anatolian fault zone for the first event and close to the strike of the Sürgü-Çardak fault system for the second one. For the first earthquake, our estimates of the rupture duration and its length (t = 52.5 s, L = 180 km) probably refer not to the entire rupture, but only to its main phase, confined to the northeastern segments of the East Anatolian Fault and characterized by maximum displacements and values of the released seismic moment. The values of t = 30 s and L = 180 km that we obtained for the second earthquake fully characterize the entire rupture.

A new method is proposed for analytical description of the magnetic field of Mercury from the data of satellite missions based on the local and regional versions of the linear integral representation method. The inverse problem on finding the sources of the field is reduced to solving ill-conditioned systems of linear algebraic equations with an approximately given right-hand side. The charts of the isolines of the z-component of the magnetic induction vector in the Cartesian coordinate system rigidly connected with the planet, as well as the regional S-approximation of the field radial component are plotted. The results of the mathematical experiment on analytic continuation of the magnetic field towards the sources are presented.

An overview of the results obtained by foreign seismologists based on the records of Turkish seismic networks AFAD (State Agency for Disaster Management under the Ministry of Internal Affairs) is presented. The sequence of earthquakes began with the M7.8 main shock and includes thousands of aftershocks. The strongest events occurred in the first twelve hours, with the sources of two M7.0+ events located 100 km apart. Earthquakes have caused ground motions that are destructive to structures, the so-called “pulse-like waveforms,” and epicentral distances, as was previously noted, are not a good indicator of attenuation of waves from earthquakes with extended ruptures.The records of stations in the near-fault zones clearly revealed the directivity effects of seismic radiation. The M7.8 earthquake (main shock) was larger than expected in the current tectonic setting. The near-field records traced an early transition to the super-shear (~1.55V_s) rupture propagation on the Narli lateral fault, where the rupture originated and then passed into the East Anatolian fault. The early transition to the super-shear stage obviously contributed to the further propagation of the rupture and the initiation of slips on the East Anatolian fault. A dynamic fracture model has been constructed that matches the various results of inversions obtained by different authors and reveals spatially inhomogeneous rupture propagation velocities. Super-shear velocities exceeding the shear wave velocity V_s are observed along the Narli lateral fault and at the southwestern end of the East Anatolian fault. Since the late 1990s, seismologists have been working on incorporating the rupture directivity effects of extended sources into the probabilistic seismic hazard analysis procedures, but no consensus has been reached so far, and progress in this area can only be expected with the accumulation of a sufficient amount of observational data.