Geodesy and Geodynamics最新文献

After the first Earth Orientation Parameters Prediction Comparison Campaign (1st EOP PCC), the traditional method using least-squares extrapolation and autoregressive (LS + AR) models was considered as one of the polar motion prediction methods with higher accuracy. The traditional method predicts individual polar motion series separately, which has a single input data and limited improvement in prediction accuracy. To address this problem, this paper proposes a new method for predicting polar motion by combining the difference between polar motion series. The X, Y, and Y-X series were predicted separately using LS + AR models. Then, the new forecast value of X series is obtained by combining the forecast value of Y series with that of Y-X series; the new forecast value of Y series is obtained by combining the forecast value of X series with that of Y-X series. The hindcast experimental comparison results from January 1, 2011 to April 4, 2021 show that the new method achieves a maximum improvement of 12.95% and 14.96% over the traditional method in the X and Y directions, respectively. The new method has obvious advantages compared with the differential method. This study tests the stability and superiority of the new method and provides a new idea for the research of polar motion prediction.

Despite the continuous improvement of the widely used empirical model international reference ionosphere (IRI), the recently appeared new models must be tested worldwide. Testing along the meridians has the advantage of dealing with the latitudinal dependent parameters. This paper uses new models of parameters foF2 (critical frequency), TEC (total electron content), and τ (equivalent slab thickness of the ionosphere), which are of great importance for evaluating the effects of space weather. IRI-Plas, NNT2F2, and NTSM models were tested using data from 6 ionosondes located along the meridian 110° E in March 2012. It is shown that the IRI-Plas model provides the closest values to experiment with respect to τ, while the NTSM model provides a rather limited reflection of the latitude dependence. Analyses of foF2(NNT2F2) have shown that, the NNT2F2 model provides good conformity with experimental values in this area, but it is very dependent on the TEC processing method. The latitudinal dependences of foF2 obtained with TEC and polynomial dependence τ(Appr) showed the presence of positive deviations from medians not only during disturbances but also quiet periods, longitudinally at the meridian.

This study explains the multi-decadal shoreline changes along the coast of Kanyakumari from 1980 to 2020. The shorelines are extracted from the Landsat images to estimate the shoreline dynamics and future predictions using Digital Shoreline Analysis System (DSAS). By the estimation of End Point Rate (EPR) and Linear Regression Rate (LRR), it is quantified that the maximum erosion is 5.01 m/yr (EPR) and 6.13 m/yr (LRR) consistently with the maximum accretion of 3.77 m/yr (EPR) and 3.11 m/yr (LRR) along the entire coastal stretch of 77 km. The future shoreline predicted using the Kalman filter forecasted that Inayam, Periyakattuthurai and Kodimunai are highly prone to erosion with a shift of 170 m, 157 m and 145 m by 2030 and 194 m, 182 m and 165 m by 2040 towards the land. Also, the western coast is highly prone to erosion and it is predicted that certain villages are prone to loss of economy and livelihood. The outcome of this study may guide the coastal researchers to understand the evolution and decision-makers to evolve with alternative sustainable management plans in the future.

Through analysis and generalization of more than 50 years of monitoring data pertaining to geomagnetic earthquake precursors in landfills across Uzbekistan involving repeated route and area surveys and stationary observations, as well as extensive data retrieved from the study of the complex in foreign countries, models of long-, medium- and short-term earthquake precursors were created for the first time. Medium- and short-term data were mainly studied based on monitoring data of the precursor complex considering geodynamic polygons in Uzbekistan. The analysis demonstrated that these precursors exhibit different shapes, configurations and signs. There occurred no uniform precursor form. Precursors exhibited bay-shaped forms, including both positive and negative signs, in addition to stepped, wave-oscillatory and other formats. The variety of manifestation forms primarily depends on the surrounding regions' geological and tectonic structures and the various processes in the Earth's crust.

The study aims to assess the nitrate and fluoride concentration in groundwater and its adverse effects on human health. In 2019, 42 groundwater samples were collected from various bore wells within the western Noyyal basin, India. Sodium and chloride are the dominant cation and anion, respectively. The nitrate concentration in groundwater samples varies from 2 to 89 mg/L, of which 33.33% are above the permissible limit of 45 mg/L for drinking water. The fluoride concentration ranges from 0.2 to 2.4 mg/L, with 28.57% of the samples exceeding the safe value of 1.5 mg/L for drinking water. Correlation plots demonstrate that the potential of hydrogen (pH), electrical conductivity (EC), total dissolved solids (TDS), ${\text{Na}}^{+}$ and ${\text{HCO}}_3^{-}$ are positively correlated with ${\text{F}}^{-}$, whereas ${\text{Ca}}^{2+}$ is negatively correlated. Mixed Ca–Mg–Cl is the most common water type in the investigated region. The Gibbs diagram demonstrates that the interaction between rock and water impacts the groundwater chemistry. Using the method of the United States Environmental Production Agency (USEPA), this study assesses the non-carcinogenic health risk posed by nitrate and fluoride in different age groups (infants, children, and adults). The values of total hazard index (THI) vary from 0.59 to 10.07 (mean = 4.76) for infants, 0.36 to 6.23 (mean = 2.95) for children, and 0.19 to 3.32 (mean = 1.57) for adults. Furthermore, 97.62%, 92.86%, and 73.81% of the samples surpass the recommended limit (THI = 1) for infants, children, and adults, respectively. Thus, the health risk assessment (HRA) indicates that infants and children are more susceptible to non-carcinogenic health hazards than adults. The THI spatial variation map shows that central and southern regions of the study area have been identified as high health risk areas (THI >3.0) for all age groups.

It is well known that seismic hazard assessment should be implemented to design infrastructures in an earthquake-prone area such as Bengkulu. This paper presents local seismic hazard maps based on the response spectra of stiff and very dense soils in Bengkulu city, Indonesia. We collect the soil data and conduct the seismic wave propagation. The input motion for wave propagation analysis is generated from the spectral acceleration curves of stiff and dense soils. Various ground motion parameters such as peak ground acceleration, short-period and long-period spectral accelerations, and amplification factors are presented in microzonation maps. The results show that the peak ground acceleration in the study area ranges from 0.2 to 0.8 g, while the spectral acceleration varies between 0.5–1.5 g and 0.4–0.8 g for periods of 0.2 and 1 s, respectively. The amplification factor of the site is observed to vary from 0.5 to 1.6. Considering other spectral accelerations in Bengkulu, the spectral acceleration design shows a good performance. The results indicate the site characteristics of Bengkulu city, which can provide engineers with site class for structural building design.

For the current geological mapping of individual territories, remote sensing and geographic information system (GIS) technologies are widely used. Taking the Fergana depression as an example, this paper aims to determine the possibilities of using remote sensing materials for mapping structural and geomorphological elements. Landsat-8 satellite imagery obtained on 11 spectral channels was used to highlight the decoding features. Fault zones, lineament zones, various uplifts, depressions, and structural material complexes of different ages were identified. Based on the in-depth analysis of geological and geophysical data, a geological schematic map of the Fergana depression was developed. Using geological landscape and automated methods for deciphering space images, the main neotectonic elements of the Fergana depression were identified: the southern step, northern marginal slope, central graben-syncline, flexure-fault zones, local anticlinal zones, individual uplifts/depressions, and local shear zones. The results show a neotectonic map of the study area, which can be used as a tectonic basis for prospecting, seismic zoning mapping, and geological engineering development.

Numerous geophysical studies have revealed the lithospheric structure of the Qiangtang and the Songpan-Ganzi terranes in the eastern Tibetan Plateau. However, crust–mantle evolution and crustal response to the Indian lithospheric subduction are still controversial. Answering these questions requires additional information regarding crustal structure. In this study, the 2-D normalized full gradient (NFG) of the Bouguer gravity anomaly was used to investigate anomalous sources and interpret the crustal structure underneath the Qiangtang and Songpan-Ganzi terranes. The NFG-derived structures with low-order harmonic numbers (N = 33 and N = 43) showed that an anomalous source beneath the southern Qiangtang terrane had a characteristic northeastward-dipping shape, suggesting the northeastward motion of the crustal material induced by underthrusting Indian lithospheric mantle. The NFG images with harmonic number N = 53 showed a large-scale anomalous source in the lower crust of the transformational zone from the Qiangtang terrane to the Songpan-Ganzi terrane, consistent with thickening crust and resistance of lower crustal flow. The anomalous source demonstrated by the NFG results with harmonic number N = 71, located in the upper crust underneath the Ganzi-Yushu fault, suggested a seismogenic body of the 2010 M_W6.9 Yushu event.

The unique seasonal surface dust storms on Mars have a significant impact on the Martian atmosphere. However, due to the lack of observations, semi-empirical models are difficult to simulate the density changes in the thermosphere with the existence of dust storms in detail. Data from multiple Mars probes now offer new opportunities to study the detailed response of Martian dust storms to the upper atmosphere. In this paper, we use MAVEN accelerometer and mass spectrometer to study the variations of the Martian thermosphere density in autumn between MY 32 and MY34 (The corresponding Earth dates: February 11, 2015 to February 28, 2019), and use the seasonal model with dust storm index to fit the annual data of the above three Martian years. The results show that the thermosphere density has a clear response to the surface dust storm activity. Furthermore, the spatial distribution of measured data in autumn (northern hemisphere) is compared with the atmospheric density distribution simulated by the general circulation model (GCM) under specific initial conditions. The model simulation results agree well with the thermospheric density distribution characteristics of each Martian year under the initial strong dust storm conditions. It proves the important role of global dust storm in changing the structure of the Martian thermospheric atmosphere.

Impact of satellite elevation cutoff angle and position dilution of precision (PDOP) mask change on epoch-wise variance components of unmodeled effects that accompany relative Global Positioning System (GPS) positioning is presented herein. Data used for this study refer to the winter and summer periods of the years with minimal (2008) and maximal (2013) solar activity. These data were collected every 30 s in static mode, at two permanent GPS stations located in Montenegro, establishing a medium-distance (116-km-long) baseline with a height difference of approximately 760 m between its endpoints. The study showed that changing satellite elevation cutoff angle, with a fixed PDOP mask, affects epoch-wise two-way nested ANOVA estimates of variances related to the ‘far-field’ multipath (considered as the nested factor herein) and the combined unmodeled effect of tropospheric and ionospheric refraction (considered as the nesting factor herein). However, changing of PDOP mask, with a fixed satellite elevation cutoff angle, doesn't affect epoch-wise two-way nested ANOVA estimate of variance of the combined unmodeled effect of tropospheric and ionospheric refraction, but, generally, affects the estimate of variance of the ‘far-field’ multipath (possibly mixed with a part of a ‘shorter-term’ ionospheric refraction), which is especially pronounced for the summer period. It should also be noted that there is a significant influence of satellite elevation cutoff angle change on both epoch-wise horizontal and vertical position accuracy, only for the summer period, especially in the presence of maximal solar activity, while there is no significant impact of PDOP mask change on epoch-wise positional accuracy.