Electrical resistivity tomography investigations on a paleoseismological trenching study

Two-dimensional electrical resistivity tomography (ERT) investigation was performed in a paleoseismological trenching study. Data acquisition strategies such as the selection of electrode configuration and electrode intervals of ERT application were investigated in this paper. The ERT results showed that the Wenner and Wenner-Schlumberger arrays yielded similar results for subsurface characteristics whereas the DD array provided slightly different results. The combined usage of these arrays produced satisfactory images of the subsurface resistivity distribution. In addition, the electrode spacing tests revealed that a suitable interpretation of subsurface geology can be obtained from a 5 m electrode interval. However, a suitable trenching location defined by successful 2D resistivity models was obtained for 1 m electrode spacing. Therefore, the comparison of the trench and ERT results was also possible. The results of trenching and ERT studies substantially support each other. (C) 2014 Elsevier B.V. All rights reserved

Imaging of multilayered archaeological settlements using electrical resistivity inversion method

Farklı arkeolojik dönemlere ilişkin karmaşık arkeolojik konteks içeren çok katmanlı höyük türü yerleşmeler arkeolojide önemli araştırma alanlarından biridir. Bu tez çalışmasında, elektrik özdirenç ters-çözüm (elektrik özdirenç tomografisi-ERT) yönteminin veri toplama ve ters-çözüm stratejileri höyük türü arkeolojik yerleşmeler bağlamında benzetim ve arazi çalışmaları yardımıyla araştırılmıştır. ERT sonuçları, farklı elektrot dizilimleri (Wenner-alfa, Wenner-Schlumberger, dipol-dipol, pol-pol ve pol-dipol), profil ile elektrot aralıkları ve profil yönlenmesi etkileri göz önüne alınarak test edilmiştir. Ayrıca, yöntemin gömülü yapılar ile farklı arkeolojik dönemlere ilişkin yerleşim mimarisini görüntülendirmedeki başarısı incelenmiştir. Yöntemin 3-boyutlu uygulamalarında düz ve ters-çözüm değerlendirmeleri ticari ve geliştirilen Matlab tabanlı programlar ile gerçekleştirilmiştir. Bu değerlendirmelerde, bloklu ve düzgünlük-kısıtlı ters-çözümler kullanılırken, düz-çözüm ise sonlu-elemanlar ve sonlu-farklar yaklaşımları ile başarılmıştır. Modelleme ve arazi çalışmaları, ERT yönteminin arkeolojik yapı ile örtü toprak arasında yeteri bir özdirenç zıtlığı bulunması durumunda başarılı yeraltı görüntüleri ürettiğini göstermiştir. Ayrıca Matlab tabanlı programın, ticari yazılıma oldukça benzer sonuçlar verdiği belirlenmiştir. Değerlendirmelerde kısmi-3B görüntüler yetersiz bir çözünürlüğe sahipken, yarı-tam 3B çözümler yeraltının daha yorumlanabilir görüntülerini vermiştir. Dizilim araştırmalarında ise, dipol-dipol, pol-pol ve pol-dipol dizilimleri Wenner ve Wenner-Schlumberger dizilimlerine göre daha nitelikli görüntüler sunmuştur. Profil ve elektrot aralıkları ile profil yönlenmesinin etkileri de bu çalışma ile ortaya çıkarılmıştır. Böylece, yöntemin veri toplama ve değerlendirme aşamalarında uygun yolların izlenmesiyle yeraltının 3-boyutlu özdirenç dağılımı ayrıntılı olarak belirlenebilmekte ve gömülü yapıların yorumlanması daha kolay bir biçimde yapılabilmektedir. Sonuç olarak bu tez çalışması elektrik özdirenç ters-çözümünün höyük türü yerleşmelerin çok katmanlı stratigrafisinin görüntülendirilmesinde önemli bir araç olabileceğini ortaya koymuştur. In archaeology, multilayered settlements (höyük, tell, tepe) are among the most important sites for investigation and excavation. This type of site is a sub-circular, nucleated settlement composed of mud and stone-based materials remaining from different archaeological times; it presents a complex archaeological context. This thesis discusses the usefulness of the data acquisition and inversion facilities of electrical resistivity inversion (electrical resistivity tomography-ERT) method to define buried structures and settlement plans of various archaeological layers of the höyük. ERT results were analyzed according to the effects of different electrode arrays (Wenner-alfa, Wenner-Schlumberger, dipole-dipole, pole-pole and pole-dipole), line and electrode intervals and line orientations in the context of simulation and field studies. The inversion of the apparent resistivity data were achieved using a developed code in Matlab and commercial software. The robust and smoothness-constrained inversion techniques were performed during the evaluations in which the forward solution was achieved using the finite-difference and finite-element approaches. Modelling and field studies reveal that the ERT method produces satisfactory subsurface images if there is sufficient resistivity contrast between the archaeological structures and covering soil of them. Developed Matlab code shows a good correlation with the commercial software. The ERT results indicate that a semi-fully 3D investigation provides more accurate solutions than quasi-3D applications. In the course of array investigations, dipole-dipole, pole-pole and pole-dipole arrays present more informative images than the Wenner and Wenner-Schlumberger. The inter-electrode and inter-line spacing, as well as the line orientation effects, were also investigated during the studies. Therefore, a reasonable field and inversion strategies for ERT studies of the multilayered settlements are suggested. The results of this thesis conclude that ERT is a highly suitable technique for the determination of settlements that have layered stratigraphy

Integrated geophysical investigations in a fault zone located on southwestern part of Izmir city, Western Anatolia, Turkey

Integrated geophysical investigations consisting of joint application of various geophysical techniques have become a major tool of active tectonic investigations. The choice of integrated techniques depends on geological features, tectonic and fault characteristics of the study area, required resolution and penetration depth of used techniques and also financial supports. Therefore, fault geometry and offsets, sediment thickness and properties, features of folded strata and tectonic characteristics of near-surface sections of the subsurface could be thoroughly determined using integrated geophysical approaches. Although Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT) and Seismic Refraction Tomography (SRT) methods are commonly used in active tectonic investigations, other geophysical techniques will also contribute in obtaining of different properties in the complex geological environments of tectonically active sites. In this study, six different geophysical methods used to define faulting locations and characterizations around the study area. These are GPR, ERT, SRT, Very Low Frequency electromagnetic (VLF), magnetics and self-potential (SP). Overall integrated geophysical approaches used in this study gave us commonly important results about the near surface geological properties and faulting characteristics in the investigation area. After integrated interpretations of geophysical surveys, we determined an optimal trench location for paleoseismological studies. The main geological properties associated with faulting process obtained after trenching studies. In addition, geophysical results pointed out some indications concerning the active faulting mechanism in the area investigated. Consequently, the trenching studies indicate that the integrated approach of geophysical techniques applied on the fault problem reveals very useful and interpretative results in description of various properties of faulting zone in the investigation site. (C) 2016 Elsevier B.V. All rights reserved

Electrical Resistivity Tomography Investigations of Multilayered Archaeological Settlements: Part II - A Case from Old Smyrna Hoyuk, Turkey

To determine the data acquisition and inversion capabilities of electrical resistivity tomography (ERT), which is used in multilayered archaeological settlements, an ERT survey was carried out at the Old Smyrna Hoyuk site, in the city of Izmir, Turkey. This site dates from the third millennium bc and ERT applications were performed using five different arrays (Wenneralpha, WennerSchlumberger, dipoledipole, polepole and poledipole). The resistivity distribution of the subsurface was investigated by two-dimensional and three-dimensional inversion routines, which use data obtained along orthogonal lines. To test the inversion treatments, semi-fully three-dimensional and quasi-three-dimensional approaches were also investigated, and comparison indicated a clear distinction between them. The results show that the quasi-three-dimensional solution had insufficient resolution, whereas the semi-fully three-dimensional data sets provide interpretable images of the subsurface. In addition, the effects of electrode array type and line interval and orientation were tested to define suitable ERT survey strategies for multilayered archaeological settlements. The array investigations show that dipoledipole, polepole and poledipole arrays presented better quality images than the others. The line orientation tests performed in two perpendicular directions (NS and EW oriented lines) show that the NS oriented lines are more suitable in terms of defining the buried architectural plan of Old Smyrna Hoyuk according to depth-slicing visualizations. However, the combination of the two perpendicular data sets could be useful if large between-line intervals are used. Finally, this ERT study clearly revealed the layered stratigraphy of Old Smyrna Hoyuk. Copyright (C) 2011 John Wiley & Sons, Ltd