Journal of Earth System Science最新文献

Deciphering geological phenomena, including planetary evolution, is accomplished by studying Earth’s impact craters. An attempt has been made to identify the buried lineament anomalies using multisensor satellite data in the Aorounga impact structure in Chad, Africa. In order to improve the visibility of buried lineaments, interferometric synthetic aperture radar (InSAR) coherence, backscatter coefficient, land surface temperature (LST), and digital elevation model (DEM) were processed. The analysis of InSAR coherence data reveals that coherence values are low to moderate in disparate regions encompassed by dune systems with rocks and higher in monotonous areas like dynamic dunes and fractured rock exposures. The results show that backscattering coefficient values of VV and VH polarization decreased in buried lineament regions covered by dunes, whereas high backscattering is experienced in regions encompassed by rocks. It was observed that nighttime has the highest LST in the linear features, whereas daytime LST is found to be low in buried lineaments regions. Thus, in this study, the backscatter coefficient of VH and VV polarization and DEM give promising interpretations to other methods for identifying buried lineament features. The study has demonstrated the potential of multisensor satellite data for identifying buried lineament anomalies that could be potential sources of groundwater, minerals, and hydrothermal activity. These anomalies may also be indicators of tectonic and structural activities.

Abstract

The stability of tunnels in jointed rock masses can be compromised by seismic activity, making it important to understand the characteristics of waves and rock joints. This study investigates the dynamic response of two intersecting tunnels under varying input wavelength and amplitude and the influence of joint density and stiffness on their behaviour using the DEM–DFN approach. A discrete fracture network (DFN) interlay was incorporated into a distinct element method (DEM) model domain to simulate weak zones in rock masses. Analysis shows that higher fracture density reduces shear stress near the DFN interlay, while joint stiffness affects wave transmission, causing a significant drop in shear stress upon wave entry. The increase in joint density and change in interlay thickness intensified the amplification of reflected waves, resulting in wave interference and reduction in transmission waves. For tunnel intersections within the DFN interlay, the larger of the two tunnels, or the main tunnel, experienced substantial deformation when peak ground velocity (PGV) was between 0.05 and 0.25 m/s, while the smaller or access tunnel exhibited maximum displacement only when PGV exceeded this range. Amplification of waves was significant when the ratio of wavelength to tunnel diameter (λ/D) was 10, while λ/D > 75 produced a response similar to uniform quasi-static loading. Tunnel joints with stiffness exceeding 100 GPa/m experienced substantially lower deformations, while those with higher fracture volumetric intensity (P₃₂ = 2 m²/m³) led to reduced wave propagation. The size of the intersection also influenced the deformation of both tunnels, with larger intersections resulting in greater deformation.

Research highlights

• The study examines wave propagation through discrete fracture network interlay of varying thickness

• Dynamic response of intersecting tunnels in jointed rock mass simulated using coupled distinct elements and discrete fracture networks.

• Investigation of the impact of wavelength, amplitude, joint density, and stiffness on tunnel intersection behaviour.

Abstract

The December 26, 2004 tsunami waves caused significant destruction that changed geomorphic characteristics in India’s east coast. The article presents a comparative study of granulometric and granule trends of pre-tsunami (December, 2004) and post-tsunami (January, 2005) sediments with recent beach sediments (December, 2022) in eight locations, namely, Poompuhar, Chinnankudi, Kuttyandiyur, Chandrapadi, Kottucherimedu, Karaikal Beach, Vadakku Vanjiyur North, and Nagoor Beach. The study was conducted using R Programming and aimed to understand the sediment transport and depositional processes. The textural parameters of the sediments imply that they are becoming relatively finer, stating that the beaches are recovering and reclaiming their regular depositional environment after the disaster. The linear discriminate function plots of pre-tsunami sediments have the highest percentage of aeolian deposits, followed by post-tsunami. The recent sediments have the maximum deposition by the beach environment, and pre-tsunami sediments have the minimal. CM plots show that the transportation of sediments by rolling is more in recent days, whereas sediments were transported by bottom suspension and rolling and by graded suspension in pre- and post-tsunami environments. Further, this study compared sediment roundness between the pre- and post-tsunami periods and the recently deposited sediments. This paper highlights the sediment characteristics observed, especially in the aftermath of natural disasters such as tsunamis.

Research highlights

• The study provides valuable insights into the origin of the debris, historical transportation, and depositional activities along the coast.

• The study of pre-, post-tsunami and recent beach sediments along the coast from Nagoor to Poompuhar have been done, in which, the sediments have become relatively coarser from pre to post tsunami deposition condition and in recent deposition, the sediments are becoming relatively finer.

• The pre-tsunami sediments have the highest percentage of aeolian deposits, followed by post-tsunami. In contrary, recent sediments have the maximum deposition by beach environment.

• The transportation of sediments by rolling is more in recent days.

• The beaches are recovering and reclaiming their regular depositional environment in recent times after the disaster which is evident by this study.

The present study evaluates the annual and seasonal trends of PM₁₀, NO₂, and SO₂ for eight monitoring stations namely Kidwai Nagar (S1), Jareeb Chowki (S2), Panki Site 1 (S3), Shastri Nagar (S4), Awas Vikas Kalyanpur (S5), Dada Nagar (S6), IIT Campus (S7) and Rama Devi (S8) in Kanpur city, India for the period 2016–2020. It was observed that the annual average concentrations of RSPM, NO₂, and SO₂ varied from 100.40 to 307.50, 9.69–60.74, and 2.00–12.04 µg/m³, respectively, for the study period, indicating that the pollutants exceeded the prescribed standards except SO₂ at all the study locations. Seasonal analysis shows that the minimum and maximum concentrations of RSPM existed for monsoon and winter, varying between 56.14 and 372.64 µg/m³, respectively. Seasonal analysis for gaseous pollutants (SO₂ and NO₂) showed minimal variations with concentration ranges between 2.00–10.97 and 12.56–57.66 µg/m³, respectively. This could be attributed to constant emission sources and year-round industrial operations prevalent within the city. Exceedance factors based on RSPM and NO₂ indicated that PM₁₀ was the most critical pollutant for Kanpur city. Results obtained from the HYSPLIT model depicted poor measures of air quality in the city, with winds blowing from a northerly direction, leading to increased concentration of pollution that exceeded the NAAQS standards. A critical discussion of the results obtained has been presented.

This paper discusses the upgraded data assimilation (DA) wave forecasting system at the Indian National Centre for Ocean Information Services (INCOIS). Significant wave height (SWH) observations from deep and shallow water buoys in the North Indian Ocean are incorporated into the assimilation system in conjunction with satellite observations from SARAL/AltiKa, Jason-3, Sentinel-3a, and Sentinel-3b. In deep water, satellite DA improved the SWH forecast by ~16%, and the inclusion of buoy observations enhanced it up to ~43% in the initial forecast hours. The impact of satellite DA persists throughout the forecast period of 5 days for swell height, with 11–27% improvement. Ingestion of buoy observations further improved it up to ~31.5% at the 3^rd hr forecast. For the wind–sea height, buoy DA resulted in an improvement of 9–26% during the initial 12 hr. In general, the positive impact of buoy DA only lasts till the 30^th hr forecast. In shallow water, the impact of satellite DA on SWH prediction is moderate, with positive improvements of 4–7.5%. Adding buoy observations significantly improved it to 10–40% in the initial 12 hr, especially for the low wave heights. Although the buoy DA improved the prediction of wave periods compared to the non-assimilated model, it tends to degrade the forecast compared to the model with satellite DA alone. This points to the limitation of the current assimilation approach in correcting the wave energy distribution in the background spectrum, particularly at higher frequencies.

Abstract

2019 witnessed one of the strongest positive Indian Ocean Dipole. A very strong positive subsurface mode (pSSM) co-evolved in the Tropical Indian Ocean (TIO) during September–October–November 2019, which strengthened further during December–January–February (DJF) 2019–2020. This is the first occurrence of such a very strong pSSM in the recent decades, which strengthened during DJF without any favourable forcing from the Pacific. The TIO further displayed anomalous basin-wide surface warming from winter 2019 to summer 2020. It is found from both observations and model experiments that ocean dynamics associated with pSSM played a major role in the TIO basin-wide warming during 2020. The subsurface–surface interaction along the downwelling Rossby wave path from boreal winter to spring, the reflected Kelvin waves and surface currents have contributed to the basin-wide surface warming of the TIO from DJF (2019–2020) onwards. The mixed layer heat budget analysis reveals that the surface heat fluxes were not favourable for the basin-wide surface warming, thereby undermining the role of any Pacific forcing through atmospheric pathways. The ocean model sensitivity experiments further highlight the importance of Indian Ocean dynamics in the co-evolution of subsurface temperature and sea surface temperature over TIO, especially during the 2019–2020 event.

Research highlights

• A strong subsurface dipole mode evolved in the Tropical Indian Ocean temperature during 2019–2020.

• Indian Ocean basin-wide surface warming persisted up to summer 2020, highlighting the role of ocean dynamics.

• Indian Ocean dynamics associated with the subsurface mode is responsible for the evolution of basin-wide surface warming.

• Ocean model experiments support the role of ocean dynamics in the evolution of basin-wide surface warming.

One of the most prominent factors contributing to global landscape cover change is land use and land cover (LULC). Such changes are the outcome of several interrelated factors. This study assessed trends in land use and land cover within Hirpora from 1992 to 2006 and 2021 utilizing remote sensing data and satellite pictures from Landsat 5-TM in 1992, Landsat 7-enhanced TM in 2006, and Landsat 8-OLI in 2021. The images were analyzed using ArcGIS v10.1 and ERDAS Imagine v14. From 1992 to 2021, there was a substantial shift in land use trends in a few targeted classes, with snow cover losing the most (33.76%), followed by dense forests (6.80%), and economically grasslands (21.46%), barren/rocky (11.43%), and scrub (5.41%) gaining the most. During the observation period, moderately dense forests and build-up increased in area by 4.50 and 0.35%, respectively. Due to large-scale human intrusion and habitat fragmentation, the Hirpora Wildlife Sanctuary has swiftly transitioned from a natural to a cultural landscape. As part of the LULC change process, natural, demographic, and economic factors have impacted land and had environmental implications.

Abstract

This study investigated the annual and seasonal mean temperature trends of North-East Indian region and surrounding territories over the period 1901–2020 with special emphasis on the trends from the recent past (1979–2020) utilising Climatic Research Unit (CRU) and ECMWF Reanalysis version-5 (ERA5) data. Spatio-temporal distribution of surface temperature across different seasons and associated biases between 1901 and 2020 were examined. The long-term trend of temperature was evaluated by linear regression for each month from the entire 120-yr period over the whole study domain. Further, Mann–Kendall and Sen’s slope test was employed to assess the magnitude of the trend at 11 selected locations of varying altitudes. Areas around Bangladesh, which are notably polluted, as well as Myanmar and the Indian states of West Bengal, Jharkhand, Bihar and Chhattisgarh exhibited notable mean temperatures than the rest of the region. Both near-surface and 2m-temperature displayed positive trends for the period 1901–1950, 1979–2020, and during the whole duration 1901–2020, despite negative trends during 1951–1978. It has been observed that the regions with relatively higher elevations have experienced a larger warming rate than the low-elevation zones.

Highlights

• Annual and seasonal temperature trends for North-East India and surrounding territories were studied.

• Mann-Kendall and Sen’s slope test was carried out for 11 selected locations.

• Post-monsoon season experienced greatest rise in mean temperatures between 1901 and 2020.

• Temperature data revealed increasing trends for periods 1901–1950, 1979–2020, but decreasing trends for 1951-1978.

• Warming rates were higher for higher elevation zones, particularly during the postmonsoon and winter months.

This study focuses on developing a relation between fundamental frequency (fo) and the depth of sediments above the bedrock. The fundamental frequency of the site ranges from 1.25 to 27.19 Hz, whereas the depth of sediments above the bedrock varies from 2 to 145 m. The eastern Shimla region has a fundamental frequency variation from 3.6 to 5.5 Hz, whereas the western and central parts have a fundamental frequency variation from 1.24 to 5.5 Hz and high frequency (>20 Hz) at isolated locations. The seismic data has also been recorded in active mode using MSOR (multichannel simulation with one receiver) to derive the dispersion curve, enabling the derivation of a 1-D, shear wave velocity (Vs) model using a joint fit modelling procedure. The 1-D profile shows variation in Vs from 180 m/s at the top to 760 m/s at bedrock. As per the National Earthquake Hazards Reduction Program (NEHRP) classification, the sites show that almost 40% of the city area fall under stiff soil and 60% fall under very stiff soil categories. Since most of the study region is covered with forest and sloping terrain, an empirical relationship (H = 154.36fo^–1.451; R² = 0.91) has been established for assessing the thickness of unconsolidated sediments. Furthermore, the thickness of sediments is determined by forward modelling by keeping the constant velocity at bedrock (Vb) 800 m/s. Additionally, the spatial map for sediment thickness is generated using the interpolation approach in combination with the forward modelling and regression analysis techniques. The derived relationship will provide major input for the area sharing similar geographical variability, where long active seismic profiles are not possible.

This research delves into the unexplored geothermal resources within Egypt’s internationally significant Red Sea and Central Eastern Desert regions, recognized for their renewable energy prospects. Surface thermal manifestations in granitic rocks, abundant in radioactive minerals, and geothermal anomalies along the depocenter regions of the Red Sea rift highlight the medium to high geothermal resources in the area. Utilizing an extensive dataset of aeromagnetic data, including derived heat flow (HF) data, geothermal surveys, and radioactive analysis of granitic rock samples, this study employs cutting-edge geophysical methodologies, particularly aeromagnetic data analysis, to identify the structural trends of the study area. The results reveal a range of medium to high heat flow values, determined through meticulous examination of the Curie depth point, temperature gradient, and HF data. Comparative analysis with seismicity data and the structural framework unveils distinct geothermal sources, setting this region apart within Egypt. The observed correlation between high-seismicity areas, structural locations, and HF map locations suggests a significant role of geodynamic motions in shaping the heat flow patterns. By highlighting the substantial geothermal potential, this study underscores the importance of advanced geophysical data in accurately identifying potential energy sources. The insights derived from this research hold global relevance, providing guidance for future exploration and development initiatives and contributing to the international discourse on transitioning to renewable energy. However, a comprehensive evaluation that incorporates radioactive analysis and exploratory drilling is crucial for fully unlocking the geothermal potential in this strategically important study area.