This paper proposes a new method for determining the seismic parameters of the subsurface below a seismic station using the waveforms of converted waves. The subsurface below the seismic station is ...represented by a plane-layered model. In contrast to other methods, the new approach does not involve determining all the elastic parameters of each of the layers. Instead, it is proposed to use a combination of parameters related directly to the object under study. In our case, we estimate the depth dependencies of the seismic velocity and density. The quality of solutions is assessed based on the rms distance between the observed waveforms and the seismograms derived from the averaged depth dependences of the seismic parameters. The approach proposed is applicable to a wide range of inverse problems in geophysics.
The peculiarities of waveforms of the P and S receiver functions, constructed from the records of three closely located broadband seismic stations, are studied. The stations are located in the Avacha ...Bay area, near the subducting part of the Pacific Plate. This is an inclined slab, which is characterized by higher seismic velocities and can cause complex patterns of seismic waves, thus distorting the waveforms of receiver functions. In order to reveal the degree of such influence, we calculated two pairs of receiver functions. To calculate the first pair, we used the seismic events where seismic waves traveled through the subducting oceanic slab; in the case of the second pair, the waves did not travel through the slab. It is shown that converted and multiple waves formed at the boundaries of the high-velocity layer considerable distort the shapes of
P
receiver functions beginning approximately 30 seconds after the main arrival. The subducting slab does not show any considerable effect on the records of the
S
receiver function. This fact empirically supports the applicability of local one-dimensional models for interpreting the receiver functions. The seismic noise, generated by the oceanic slab, limits the maximum depth of these models at around 200 km in the study area.
—Two methods for estimating station anomalies in teleseismic
P
- and
S
-wave traveltimes are considered. Both methods employ traveltimes of the conversions from the upper boundary of the mantle ...transition zone. The first method directly uses traveltimes of the converted waves; in the second method, the sought parameters are estimated based on a simple two-layer model. The both approaches yield commensurate values for the coefficient of correlation between station anomalies of
P
- and
S
-waves. The use of the model complicates the calculations but makes it possible to directly obtain the estimates of the average values of the seismic parameters of the mantle. The observation data for northern Finland are used to illustrate the discussed subject.
The application of a predictive intellectual system previously developed for the Northern Dvina River is considered for a new region—the basin of the Lena River. The use of this technology under ...conditions of another region becomes possible due to the similar formulation of the problem of forecasting and publishing new open sets of hydrological and meteorological data for the period of 1985–2019. Based on the results of observations at gauging and meteorological stations, the system makes it possible to form a short-term forecast of the formation of powerful ice jams in river sections under conditions of incompleteness and data gaps. Interpolation methods based on machine learning are used to prepare the initial data and eliminate gaps. Calculations have shown the efficiency of the predictive system. The estimated accuracy of forecasting is 76%. The assessment of the importance of the factors have shown the common influence of groups of factors in different regions on the final result of the ice jamming process.
The article analyzes the development of ideas about the seismicity of the western sector of the Russian Arctic, which is directly related to the peculiarities of development of instrumental ...observations in the region. The current ideas about the seismicity of the western sector of the Russian Arctic are generalized. Throughout the 20th century, the development of instrumental observations in the Eurasian Arctic, of which the western sector of the Russian Arctic is a part, has been both temporally slow and spatially uneven. In the Eurasian Arctic, seismically active regions, such as mid-ocean ridges, the Svalbard archipelago, the Laptev Sea shelf, and the Taimyr Peninsula, have become the object of study. Conversely, the central and eastern parts of the Barents–Kara region, which are part of the western sector of the Russian Arctic, have always had poor instrumental completeness and, accordingly, the extent of seismic knowledge has been poor. The intensive development of instrumental observations in the Eurasian Arctic in the 21st century has made it possible to significantly expand understanding of the seismicity of the western sector of the Russian Arctic. The greatest seismicity is manifested within the continent–ocean transition zone and Kvitøya (Bely) Island, and the Novaya and Severnaya Zemlya archipelagos. The shelf of the Barents and Kara seas itself is characterized by rare and scattered seismicity. However, the existing seismic network is insufficient for detailed studies of sp-atiotemporal variations in the seismicity of individual seismically active zones and a more correct understanding of its relationship with the geological structure of the region and geodynamic processes developing therein. Long-term studies with bottom seismometers are needed.
An overview of applications of geomagnetic data for practical purposes is presented. Many of them involve models of the Earth’s main magnetic field and spatial distribution of anomalous magnetization ...of the upper lithosphere as input parameters. Unmanned aerial vehicles (UAVs) can significantly improve the efficiency of detecting magnetic anomalies.
This paper briefly reviews modern approaches and methods for generating digital elevation models. The focus is on photogrammetric model generation methods: photogrammetry itself relies on a series of ...overlapping photographic images. In our study, a camera was mounted on an unmanned aerial vehicle (UAV). We describe the major steps in generating digital elevation models, gear requirements, image capture details, and software used. Lastly, we show how we created a local digital elevation model of part of an island near the northern shore of Lake Ladoga.
The article presents the results of seismoacoustic studies carried out in Petrozavodsk Bay of Lake Onega. The goal was to study a near-surface geological section. Seismoacoustic studies were done by ...the reflection method in a modified ultra-high-resolution seismic survey. The data were office processed and interpreted: five seismic complexes were identified and correlated with information on the lake’s structure, culminating in maps of all five identified reflectors covering all of Petrozavodsk Bay. It was possible to estimate the abundance and thickness of sediments corresponding to each complex.
To obtain an image of the deep structure of the Tien Shan in central Asia, we invert P and S receiver functions jointly for almost 40 local broad-band seismograph stations. The inversion is performed ...using a simulated annealing technique. The combined inversion is an improvement on earlier studies, where P and S receiver functions were inverted separately. Using this approach, we deal with structural imaging problems that are usually investigated with teleseismic body wave and surface wave tomography techniques. We demonstrate that the uppermost mantle in the north of the central Tien Shan is composed of a high-velocity lid a few tens of kilometers thick above a pronounced low-velocity zone. The crustal structure in this region provides evidence of magmatic underplating. These features are likely related to a small plume that is manifested by basaltic eruptions of Cretaceous–Paleogene age. The low-velocity layer is also found in a southeast trending corridor, which may correspond to the Bachu uplift in the Tarim basin. Crustal thickness beneath the orogen varies from about 45 to about 70 km. The smallest values, most likely inherited from the pre-orogenic era, are found in a neighborhood of the Talas–Fergana fault. Similar values are characteristic of the Kazakh shield in the north and the Tarim basin in the south. The largest values are found beneath the bounding ranges. We infer that uplift of the central Tien Shan is unlikely to be caused by crustal shortening alone.
