Ali Ismet Kanli

Imaging of buried 3D objects by using electrical profiling methods with GPR and 3D geoelectrical measurements

Detection of near-surface buried objects is usually carried out along one or more survey lines and processed by 2D inversion algorithms. Problems arise if the target is three dimensional. The effect of the 3D objects near the profile strongly depends on the type of the electrode array, and the three-dimensional object located beneath the survey line is also mapped differently to the 2D plane. The indications of 3D objects on a 2D resistivity section depend on each electrode configuration. Theoretical calculations above 3D objects have been carried out in order to examine the problems arising from 2D inversion in the cases of four different electrode arrays (pole–pole, dipole–dipole, equatorial dipole, Wenner alpha). The results of the modelling processes give some useful information which can make it possible to rank the examined arrays from the point of sensitivity for 3D effects and the quality of imaging the object. Test measurements have been carried out in order to prove the conclusions of the theoretical investigations. Two perpendicular survey lines have been measured above a buried cellar using dipole–dipole, pole–pole and Wenner arrays. The 2D pseudosections were compared with the results of the GPR and 3D geoelectric measurements.

Image Reconstruction in Seismic and Medical Tomography

Tomography has been used for more than 40yr in medical science and its success is well known. One of the most important reasons for the success of medical tomography compared to seismic tomography is the data-acquisition geometry. A data-acquisition geometry similar to the one used in medical tomography was designed and tested with synthetic geological models. Geophysical-type data-acquisition geometries were also applied to the geological models, and the resulting images were compared to the medical images. The reconstructed image obtained in the medical case resembled the synthetic geological model and had higher resolution than the geophysical image. Secondary attention is drawn to the determination of the differences between the low- and high-velocity zones in the final image reconstruction of the tomographic inversion process. Therefore, the step-like high- and low-velocity embedded layer models were tested with different spreading systems. The geological models were also tested with one-dimensional ...

A general approach for porosity estimation using artificial neural network method: a case study from Kansas gas field

This study aims to design a back-propagation artificial neural network (BP-ANN) to estimate the reliable porosity values from the well log data taken from Kansas gas field in the USA. In order to estimate the porosity, a neural network approach is applied, which uses as input sonic, density and resistivity log data, which are known to affect the porosity. This network easily sets up a relationship between the input data and the output parameters without having prior knowledge of petrophysical properties, such as porefluid type or matrix material type. The results obtained from the empirical relationship are compared with those from the neural network and a good correlation is observed. Thus, the ANN technique could be used to predict the porosity from other well log data.

The importance of the spread system geometry on the image reconstruction of seismic tomography

The influence of spread and shot systems is investigated using common measuring geometries like conventional crosshole and multi-offset VSP. Both synthetic and field data are used to understand better the importance of commonly used spread and shot systems in the image reconstruction process. In the synthetic case, a faulted structure under a near-surface low velocity layer is used. The results of the seismic images compared with the original model and the similarities in the structure and in the velocities are investigated. Tomograms derived from the real data are compared with ground truth. Our study shows that realistic spread systems can produce nearly the same quality images as in the ideal ones.

A Systematic Geophysical Approach for Site Response of the Dinar Region, Southwestern Turkey

On 1 October 1995, the Dinar earthquake (Mw 6.1) devastated the city of Dinar in southwestern Turkey. We investigated the effects of geological conditions on the localized damage patterns using microtremor survey and multichannel analysis of surface waves. The microtremor survey was carried out in and around the Dinar basin to determine the resonance frequencies and depths of the sedimentary layer at 38 different locations using a broadband seismometer. The shear-wave velocity profile of the basin sediments was estimated from the inversion of the microtremor horizontal-to-vertical spectrum based on surface waves from seismic noise at each site using a genetic algorithm. The average shear-wave velocities estimated from the multichannel analysis of surface waves experiments were given as constraints in the inversion. A new relationship between the thickness of basin sediment and the main peak frequency in the horizontal-to-vertical spectral ratios was derived. This relationship allows a zonation of the Dinar region, which is consistent with previous studies and can be importantly used for the seismic hazard evaluation of the region.

Estimating shear wave velocities in oil fields: a neural network approach

In this study, we applied the back-propagation Artificial Neural Network (ANN) technique to test the shear-velocity for the two wells from an oil field in southeastern region of Turkey estimated from an empirical relationship. The input to the neural network includes neutron porosity, density, true resistivity, P-wave velocity and gamma-ray logs which are known to affect the shearwave velocity. The correlation between the shear-wave velocity from the empirical relationship and that from the neural network is close to one in both the training and testing stages. Thus, the ANN technique can be used to predict shear-wave velocity from other well log data.

Integrated Seismic Survey for Detecting Landslide Effects on High Speed Rail Line at Istanbul–Turkey

Abstract In this study, Multichannel Analysis of Surface Waves Method (MASW), seismic refraction tomography and seismic reflection methods are used together at Silivri district in Istanbul – a district with a landslide problem because of the high speed rail line project crossing through the area. The landslide structure, border and depth of the slip plane are investigated and correlated within the local geology. According to the obtained 2D seismic sections, the landslide occurs through the East-West direction in the study area and the landslide slip plane with its border are clearly obtained under the subsurface. The results prove that the study area is suitable enough for the landslide development and this evolution also affects the high speed rail line project.

Detection and Monitoring of Subsurface Contamination by Using Geophysical Methods and Data: Case Studies of Contamination from Chemical and Biological (Biogeochemical) Processes

Monitoring and distribution of bacterial transport, bioclogging processes, imaging to infer biogeochemical processes associated with bioremediation, remediation-induced biogeochemical end-products are detectable using geophysical methods. Biogeochemical processes alter the physical and chemical properties in the subsurface, and efficient monitoring of these changes is important for successful implementation of soil and groundwater remediation. In the study, two different geophysical studies are discussed from Germany and Hungary.

Multi-channel Analysis of Surface Wave (MASW) Technique in Geotechnical Studies

The soil classification in UBC (NEHRP) and Euro codes is mainly based on the ground type and description of stratigraphic profile. In the determination of the ground type which has a direct relation with the stratigraphic profile of the investigated site, one of the 3 important parameters is used: the average shear wave velocity of the top 30 m of the soil (Vs, 30-m/s), or NSPT (blow counts/30 cm) or cu (kPa) values. Usually the Vs30 values are calculated from velocity profiles determined from borehole (down-hole or cross-hole) measurements. In that case it is necessary to drill holes down to at least 30 m depth. The SPT and CPT techniques also need appropriate, usually expensive equipments. Recently, the MASW technique (multichannel analysis of surface waves) is effectively used in the determination of Vs profiles. In this study, 1-D share-wave velocity profile obtained from a MASW profile is both correlated with the borehole data and with the result of the SPT data. A shear modulus distribution map is plotted for the geotechnical purpose.

Combination of Active (MASW) and Passive (Microtremor) Source Based Geophysical Approach

The microtremor and the MASW (Multi-channel Analysis of Surface Waves) survey were carried out to determine the shear wave velocity-depth information, resonance frequencies and the depths of the sedimentary layer in the Dinar city, Southwestern of Turkey. The shear-wave velocity profile of the basin sediments was estimated from the inversion of the microtremor horizontal-to-vertical spectrum based on surface waves from seismic noise at each site using a genetic algorithm. The average shear-wave velocities estimated from the multichannel analysis of surface waves experiments were given as constraints in the inversion. A new relationship was derived between the resonance frequency ( ) and thickness ( ) of the overlaying layer, which is given as