Contributions to Geophysics and Geodesy

Enhancing geoid modelling for accurate local geoid determination in Lagos Island: A combined GNSS and levelling approach, Eti-Osa Local Government Area, Lagos State, Nigeria

Herbert TATA, Olamilekan Babatunde OMODEJO — Tue, 24 Dec 2024 08:29:34 +0000

Lagos Island faces challenges from coastal hazards and inadequate infrastructure, making precise geoid modelling essential for urban planning, flood risk assessment, and infrastructure development. This study addresses discrepancies in height references and emphasizes the need for accurate geoid data to support spatial planning and disaster management. The main objective is to create a geoid model tailored to Lagos Island's unique geography and infrastructure needs. The research combines the Global Navigation Satellite System (GNSS) and levelling data which created a reliable framework for determining geoid heights with high precision across Lagos Island. The methodology uses spirit levelling to obtain orthometric heights and GNSS technology, precisely Promak2 differential GNSS Receiver, to collect positional data. Ninety stations were surveyed to ensure comprehensive area coverage. This data was used to develop a geoid model through geometrical interpolation, accurately representing the local geoid surface. In the independent test, where 10 points were excluded from interpolation, the modelled geoid heights showed an RMSE of 0.2 metres, with the largest and smallest absolute deviations being 0.4 metres and 0.01 metres, respectively. In the non-independent test, where all points were used for interpolation, the comparison between the computed (observed) and modelled geoid heights at the same points showed a mean deviation of −0.3 metres. The RMSE and standard deviation were both 0.1 metres, confirming the model's accuracy in determining the local geoid. This demonstrates its suitability for precise local geoid determination in Lagos Island, providing a valuable tool for spatial analysis, infrastructure planning, and disaster mitigation. The study highlights the importance of integrating traditional surveying techniques with modern GNSS technology to address coastal urban challenges.

The effects of seismic activities following the 30 October 2020 Samos Island earthquakes in Izmir and its surrounding

Tue, 24 Dec 2024 08:30:27 +0000

With the increasing rate of subduction along the Hellenic Arc in the Eastern Mediterranean, the seismic activities of the Aegean plate and Western Anatolia have markedly increased over the past decade. The increase in seismic activity is quite remarkable, starting from the coasts of Çanakkale in the north of Western Anatolia, including Lesbos Island, Samos Island, Kuşadası Bay and Datca. In this context, in order to determine the current deformation after the Samos Island earthquake that occurred on October 30, 2020, measurements were performed at six continuous GNSS stations in and around Izmir. This study is jointly managed by Dokuz Eylül University, with contributions from Konya Technical University and Atatürk University, focusing on both GNSS and seismological analyses. The preliminary results of this investigation include the evaluation of seismic impacts on the continuous GNSS stations from July 1st to December 31st, 2022.

Application of seismic refraction tomography for determining ground water potential zone in the Qularaisi area, Sulaimaniyah city, NE Iraq

Abdulla K. AMIN, Kwestan M. AHMED, Ezzadin N. BABAN — Tue, 24 Dec 2024 00:00:00 +0000

Delineating zones with the potential groundwater contains is a crucial for the effective exploration and extraction of this resource. Six seismic refraction traverses for measuring compressional wave velocities (v_p) were conducted in the Qularaisi area, northwest of Sulaimaniyah City in the Kurdistan Region of Iraq to determine the ground water potential zone in the selected area, each traverse has a total length of 230 m, with an inter-geophone spacing of 5 m. The velocities and the thickness of each layer were subsequently calculated based on the obtained data. This analysis provides insights into the geological formation and composition of the area. The interpretation results reveal the presence of three distinct geological layers. The first upper layer consists of clay topsoil deposits characterized by brittle materials, with the thickness ranging from 0 to 4.2 m and seismic velocities (v_p) between 339 and 583 m/s. The second layer, with a thickness of 4.2 to 16.8 m and v_p values between 1248 and 2650 m/s, corresponds to recent deposits of clay, sand, silt, and gravel, interpreted as unconsolidated sediments. The third layer is characterized as a consolidated marly limestone belonging from the middle Tanjero formation, occurring at depths exceeding 20 metres. This layer reflects a more compact geological structure, distinguishing it from the overlying unconsolidated materials with the v_p values ranging from 3606 to 4844 m/s. The seismic refraction results indicate that the aquifer is a sand and gravel inter-granular aquifer at the depth to the saturated groundwater layers in the area ranges from 10 to 25 m whereas lower layer of marl bed reaches to a depth of 40.2 m acts as the impermeable bed.

New methods of assessing wind erosion risk: Innovative approach to soil protection respecting windbreak effect

Tue, 24 Dec 2024 08:32:06 +0000

Research and development of new soil protection methods helps to maintain sustainable soil management and prevent the degradation of valuable agricultural resources. Wind erosion is a significant environmental issue that can severely degrade landscape, impact agricultural productivity and deteriorate air quality through increased dust emissions and atmospheric pollution. The main goal of this paper was to provide a methodological protocol for mapping and assessing wind erosion risk, taking into account protective effect of both existing and intended windbreaks. Based on the Potential Wind Erosion Risk (PWE) map, which takes into account soil and climatic conditions affecting wind erosion risk, a new map of potential wind erosion risk (RPWE) was created with the inclusion of the effect of windbreaks and their protected zones on the tolerated length of plots. Using this method, it is possible to assess wind erosion risk, model the design of new wind barriers and evaluate their effectiveness. The presented method has been developed into a web application that provides all outputs online. The assessment builds on long-term studies of wind erosion potential and methods for spatial representation of land susceptibility to wind erosion. Assessment of the current state of erosion risk with existing windbreaks as well as modelling the state when some are removed or newly planted, is fundamental when building a resilient and healthy environment. The newly developed method contributes to worldwide global land degradation prevention and offers new insights into the methodological approach for assessing wind erosion.

Preliminary estimate of current ice thickness in the Dobšiná Ice Cave by means of geophysical and geodetic methods

Tue, 24 Dec 2024 08:32:54 +0000

The presented study focuses on the Dobšiná Ice Cave, which is worldwide unique from the speleological viewpoint, belonging to the most famous caves in Europe. During the 20th century, the research of the cave was carried out within various scientific branches. In the last years, one important part of the survey is the geodetic monitoring of the ice surface by modern laser scanning methods. Since 2020, also geophysical (georadar and microgravity) research is conducted in the Dobšiná Ice Cave. In this contribution, we present preliminary results on the present ice filling thickness, based on the interpretation of vertical radargrams and 2.5D density modelling of anomalous gravity data. Maximum thickness values from georadar measurements are more than 24.5 m in the eastern part of the cave, in the lower part of the Great Hall. Roughly estimated error of the depth determination from GPR vertical sections is at the level of ±0.5 m. Results from gravimetry apparently point to the fact that the sections with largest ice thickness could be placed rather westward to the central part of the cave. This interpretation remains questionable though, still open due to missing GPR results in the central part of the cave. We hope that future additional data and 3D density modelling will help to resolve this issue.

Improving strain measurements at Tidal Station Vyhne, Central Slovakia: Technological modernization using a capacitive transducer

Tue, 24 Dec 2024 08:33:42 +0000

The year 2024 marks the 40-th anniversary of observation of Earth tides at the tidal station of Vyhne, Central Slovakia. The station was established through an international scientific collaboration in 1984. Since then, it has monitored the geodynamical phenomena almost continuously. At the beginning, the station was equipped with an extensometer with an analogue photo-recorder. Later on, the extensometer was fitted with a new sensor unit based on the principle of a capacitive transducer. The subject of this paper is the design and construction of a new sensor for measuring subtle displacements in the Earth's crust due to the action of tidal and tectonic forces. Similarly to the currently operating sensor, it is based on the simple principle of measuring voltage changes on a movable sensing electrode fastened to a quartz glass tube. However, compared to the previous analogue version, a solution using the contemporary possibilities of high computing power of a modern microcontroller as well as its integrated peripherals are employed. Measured values are stored in a flash memory in off-line mode. The device is ready for operation in on-line mode for remote data collection in real time, as well. The first recorded data indicate that the instrument is working correctly, successfully registering the tidal phenomena. However, a significantly longer measurement period is required to ensure its proper operation and to rule out any potential adverse effects. Parallel measurements are to be carried out using both the new and former sensors, and the consistency of the results shall be examined.

Estimation of anthropogenic noise effect on relative gravimeters using the COVID-19 pandemic period

Laura PÉNZEŠOVÁ, Juraj JANÁK — Tue, 24 Dec 2024 08:34:25 +0000

The COVID-19 pandemic caused by the SARS-CoV-2 virus has brought many, mostly negative, effects and consequences on human lives, health, and economic issues. However, one of the very few positive side effects of lockdown measures was a less noisy and less loaded natural environment on a global scale. Many accurate geophysical instruments are negatively affected by the noise forced by all kinds of human activities, such as traffic, mining, construction, and others. In this paper, we present our attempt to estimate the influence of anthropogenic noise in the seismic band on five superconducting gravimeters and one spring gravimeter incorporated in International Geodynamics and Earth Tide Service (IGETS) using a comparison of gravity records before and during the lockdown period. For quantification of a noise, the mean power spectral density (PSD) was used. Based on this experiment we can compare and quantify how much particular IGETS stations and instruments are affected by the anthropogenic noise. For our experiment, we used Level 1 IGETS data on selected stations with a 1-second sampling rate or 1-minute time resolution where 1-second was not available. For selected stations we estimated the contribution of anthropogenic noise to the total noise in a seismic frequency band for a particular station and instrument.