A geohazard reconnaissance study based on geoscientific information for development needs of the western region of Istanbul (Turkey)

The role of geoenvironmental information is becoming increasingly important as legislative changes have forced developers and planning authorities to consider more implications and impact on the environment of large-scale development initiatives. Therefore, integration of surface and subsurface geoscientific information for development needs has prime importance and provides a means of identifying potential problems and opportunities at an early stage in any planned development. However, from the experience of recent natural disasters, it is evident that this was not case the taken into consideration in many countries. In addition to thousands of casualties, many urbanized areas, industrial districts and large-scale engineering structures suffered severe damages from the natural hazards due to many reasons including the lack of preliminary engineering geological maps and zoning maps of the settlement areas. Turkey is one of the countries which is exposed to natural hazards such as earthquakes, landslides and floods. In particular, the devastating 1999 Kocaeli earthquake, which affected the Marmara Region of Turkey, focused the attention on densely urbanized and industrialized metropolitan areas such as Istanbul. The rapid growth of Istanbul, particularly towards west with minimal geoscientific information resulted in an overwhelming pressure on the natural environment. In addition, a large earthquake, which is expected to occur in the Marmara Sea within the next 30 years, also pose a threat to the city and its surroundings. In this study, on the basis of the geological, geomorphological and geophysical reconnaissance study, an integrated geoscientific data were collected from the western region of Istanbul and evaluated for geohazards. The paper focuses on the geological and geomorphological aspects that control the occurrence of some geohazards such as earthquake-induced liquefaction, landslides and flooding. In this context, the geological map of the region was revised and Quaternary deposits were classified into 11 units, in detail. Liquefaction-prone areas were evaluated by using geomorphological criteria based on field investigation, by the examination of the available records from 88 boreholes drilled on recent deposits and by the data from resistivity profiles. The landslides within the region were classified according to their type, relative depth and activity. In addition, fluvial and marine flood-prone areas were also delimited within the region. Finally, a series of maps such as landslide inventory maps, and maps showing liquefaction- and flood-prone areas were produced with the aid of Geographic Information Systems (GIS) to assist in designing further detailed site investigations and to reduce costs by ensuring a more focused approach to strategic planning and site selection.     

Assessment of seismic hazards for Hurghada,Red Sea,Egypt

The entrance of the southern Suez Gulf of the Red Sea is known to be an area of high seismic activity in Egypt. The high rate of seismic activity in this area is mainly related to the adjustment in motion at the triple junction between the African plate, the Arabian plate, and the Sinai microplate. The present study attempts to estimate the Probabilistic Seismic Hazard Analysis (PSHA) for Hurghada site. This was done in two steps; the first one is by estimating specific parameters for the site, such as the mean seismic activity, λ, the Gutenberg-Richter parameter, b, and the maximum regional magnitude, m _max. The second step is by selecting a ground motion parameter that is applicable to Hurghada site. The procedure permits the combination of both historical and recent instrumental data. The results of the hazard assessment, expressed as the worst case scenario, detect that Hurghada is exposed to the maximum credible earthquake event of magnitude m _max = 7.1 ± 0.31, at hypocentral distance of 31.6 ± 10 km. The possibility of the maximum Peak Ground Acceleration (PGA), which occurred in relation to this event at Hurghada site, is equal to 0.29 g. The mean return periods with the selected accelerations for Hurghada, a horizontal acceleration of 0.1 g, is expected to occur once every 74–106 years, with an average of one every 90 years. This result which obtained from the hazard assessment can be used as an input data for a seismic risk assessment.     

Geochemistry of subsurface Late Quaternary ironstones in Rajshahi and Bogra Districts,Bangladesh: implications for genetic and depositional conditions

The present study deals with the geochemistry of Late Quaternary ironstones in the subsurface in Rajshahi and Bogra districts, Bangladesh with the lithological study of the boreholes sediments. Major lithofacies of the studied boreholes are clay, silty clay, sandy clay, fine to coarse grained sand, gravels and sands with (fragmentary) ironstones. The ironstones contain major oxides, Fe₂O₃* (* total Fe) (avg. 66.6 wt%), SiO₂ (avg. 15.3 wt%), Al₂O₃ (avg. 4.0 wt%), MnO (avg. 7.7 wt%), and CaO (avg. 3.4 wt%). These geochemical data imply that the higher percentage of Fe₂O₃* along with Al₂O₃ and MnO indicate the ironstone as goethite and siderite, which is also validated by XRD data. A comparatively higher percentage of SiO₂ indicates the presence of relative amounts of clastic quartz and manganese-rich silicate or clay in these rocks. These ironstones also have significant amounts of MnO (avg. 7.7 wt%) suggesting their depositional environments under oxygenated condition. Chemical data of these ironstones suggest that the source rock suffered deep chemical weathering and iron was mostly carried in association with the clay fraction and organic matter. Iron concretion was mostly formed by bacterial build up in swamps and marshes, and was subsequently embedded in clayey mud. Within the coastal environments, the water table fluctuates and goethite and siderite with mud and quartz became dry and compacted to form ironstone.

     

Geoenvironmental studies on conservation of archaeological sites at Siwa oasis, Egypt

Siwa oasis is located in the extreme western part of the Egyptian western desert. There are several archaeological sites in the oasis; the most distinct ones are Alexander the Great temple at Aghormi hill and the Gebel El Mota tomb excavations. They have suffered due to deterioration and cracks of different kinds and some parts are getting worse as rock falls occur. From field inspection and lab analysis, it is clear that lithology plays an important role on the extent of damage. Alexander the Great temple was built over the northern edge of Aghormi hill, which consists of two distinct beds—an upper limestone bed and a lower shale one. From field survey and laboratory analysis, the shale is considered as a high expanded bed and weak in its bearing capacity, as its clay content (mainly smectite) experienced swelling due to wetting from the ground water spring underneath. Consequently, the upper limestone bed suffered from map cracking associated with rock falls due to the differential settlement of the swelled lower shale one. The temple was threatened by slope instability and had experienced many cracks. At Gabal El Mota tomb excavations, it was noticed that a comparison of tombs of the same opening size revealed that those that excavated on shale beds had cracked much more than those that excavated on limestone. This may be attributed to the low bearing capacity of excavated shale walls. The remedial measures suggested to overcome the stability problems on these archaeological sites are grouting or construction of retaining walls.     

Integrating gravimetric and interferometric synthetic aperture radar data for enhancing reservoir history matching of carbonate gas and volatile oil reservoirs

Reservoir history matching is assuming a critical role in understanding reservoir characteristics, tracking water fronts, and forecasting production. While production data have been incorporated for matching reservoir production levels and estimating critical reservoir parameters, the sparse spatial nature of this dataset limits the efficiency of the history matching process. Recently, gravimetry techniques have significantly advanced to the point of providing measurement accuracy in the microgal range and consequently can be used for the tracking of gas displacement caused by water influx. While gravity measurements provide information on subsurface density changes, i.e., the composition of the reservoir, these data do only yield marginal information about temporal displacements of oil and inflowing water. We propose to complement gravimetric data with interferometric synthetic aperture radar surface deformation data to exploit the strong pressure deformation relationship for enhancing fluid flow direction forecasts. We have developed an ensemble Kalman‐filter‐based history matching framework for gas, gas condensate, and volatile oil reservoirs, which synergizes time‐lapse gravity and interferometric synthetic aperture radar data for improved reservoir management and reservoir forecasts. Based on a dual state–parameter estimation algorithm separating the estimation of static reservoir parameters from the dynamic reservoir parameters, our numerical experiments demonstrate that history matching gravity measurements allow monitoring the density changes caused by oil–gas phase transition and water influx to determine the saturation levels, whereas the interferometric synthetic aperture radar measurements help to improve the forecasts of hydrocarbon production and water displacement directions. The reservoir estimates resulting from the dual filtering scheme are on average 20%–40% better than those from the joint estimation scheme, but require about a 30% increase in computational cost.     

The amplitude ratioPcP/P and the core-mantle boundary

Summary Using the Haskell matrix formulation, theoretical reflection coefficient curves have been calculated for a multi-layered core-mantle boundary for comparison with observational data. Two cases are considered, first when the shear velocity in the core is equal to zero and second when the core has a finite rigidity. If the velocity contrast is large between the imbedded layer and the mantle, the reflection coefficient curves for the multi-layered medium are irregular in shape as compared to those for two half-spaces, representing the core and the mantle, respectively. The reflection coefficient curves show an oscillatory character if the imbedded layer is thick and has a high velocity contrast.The observational data consist of short-period vertical-component seismograph records ofP andPcP from nuclear explosions in the Aleutian chain, Nevada, Novaya Zemlya, Kazakh and Sahara. Attenuation and geometrical spreading are taken into consideration. Four different models for the quality factorQ are applied to the observational data. The data are found to be much affected by theQ-model used for the corrections.Based on proposedQ-values, a model for the core-mantle boundary is found, characterized by two low-velocity layers at the bottom of the mantle. The thicknesses are 16.10 km (outer layer) and 19.96 km (inner layer), the compressional wave velocities 12.17 km/sec and 10.94 km/sec and the shear wave velocities are 6.29 km/sec and 5.33 km/sec, respectively. A better fit to this model is found when in addition the shear velocity in the outer core is 2.20 km/sec and the density ratio at the core-mantle boundary is 1.07. In other words, the observations favour a layer of finite rigidity in the outer core rather than a fluid one.     

Holocene landscape reconstruction in the surroundings of the Temple of Pepi I at ancient Bubastis,southeastern Nile Delta (Egypt)

In ancient Egypt, lakes, canals, and other water bodies were an essential part of the sacred landscape in which temples were embedded. In recent years, geoarchaeological research at the site of the Temple of Bastet at Bubastis in the southeastern Nile Delta has proven the existence of two water canals surrounding the temple. It has now been investigated whether these canals were connected to the Temple of Pepi I (2300–2250 B.C.E.), located approximately 100 m to the west of the Temple of Bastet. To explore the Holocene landscape genesis of the Temple of Pepi I, 15 drillings and six geoelectrical profile lines were performed in the surroundings of the temple in spring 2022. The results show loamy to clayey sediments in deeper sections of all drillings with a maximum thickness of 1.70 m, indicating a marshy or swampy depositional environment. Based on the recovered sediment sequences and archaeological remains in the vicinity of the Temple of Pepi I, the marshy or swampy area existed before the Fourth Dynasty. During the Old Kingdom (ca. 2850–2180 B.C.E.), the former marshland either dried up through natural processes or was intentionally drained and filled with sediments for subsequent use for occupation. Regarding the original research question, there is as yet no evidence for a direct connection to the canals of the Temple of Bastet.