Exploration for a cave by magnetic and electrical resistivity surveys: Ayvacık Sinkhole example, Bozdağ, İzmir (western Turkey)

Abstract

Geophysical survey techniques have been successfully applied to near-surface cave detection in karstic terrains. We used magnetic and electrical resistivity surveys to delineate the karstic structure of the Ayvacık Sinkhole, which may be considered to be a vertical cave. The magnetic-total-field-anomaly map helped reveal the metamorphic and sedimentary units in the study area. The total-horizontal-gradient map, which was based on a calculated pseudogravity anomaly, successfully identified the contact between the limestone unit and the cave system. Using these results, we positioned and carried out a vertical electrical sounding (VES) survey with a Schlumberger array along a line that consisted of 11 stations. The VES data were then processed using a 1D global optimization technique, which used a genetic algorithm and a 2D linearized least-squares algorithm. The results were generally in good agreement with each other, and together they pointed out three geologic layers: (1) an overburden layer ([Formula: see text]), (2) an approximately 25-m-thick alluvial fill (100–316 Ωm), and (3) a limestone unit (316–3162 Ωm); and also suggested the existence of a high-resistive anomaly ([Formula: see text]), possibly a karstic cave, located at the depth of approximately 40 m. Also, the results suggested that the buried limestone unit had an undulating karstic topography including a probable pinnacle structure. A synthetic modeling study was carried out, and it validated the reliability of the results. Finally, our findings indicated that the geophysical survey techniques used here were successful in detecting a cave located deep enough to make human exploration difficult.

A geophysical approach to the igneous rocks in the Biga Peninsula (NW Turkey) based on airborne magnetic anomalies: geological implications

“…In this study, pseudogravity anomaly map (Figure 11) was produced by using the same inclination and declination angles used for the RTP calculation. Because the shallow source bodies tend to produce gravity and pseudogravity anomalies with maximum horizontal gradients near their edges or boundaries (Balkaya et al, 2012;Blakely, 1995;Blakely & Simpson, 1986;Ekinci, Ertekin & Yiğitbaş, 2013), a total horizontal derivative (THD) anomaly map of the pseudogravity data was produced in the second step by using the following expression (Blakely, 1995):…”

“…Directional derivative-based techniques use horizontal or vertical gradients (derivatives), analytic signal amplitudes or their various combinations in order to enhance the edges and to outline the boundaries of the magnetic sources (e.g. Ateş et al, 2009;Balkaya, Göktürkler, Erhan, & Ekinci, 2012;Blakely & Simpson, 1986;Debeglia & Corpel, 1997;Roest, Werhoef, & Pilkington, 1992;Xu et al, 2011). Energy spectrum of the magnetic anomalies is generally used in spectral analysis methods in order to determine the mean depth of the causative geological sources which enables to estimate the depth and thickness of the sources (e.g.…”

Metaheuristics in applied geophysics

“…Bir boyutlu (1B) örnekler kapsamında hem kuramsal (yapay) hem de arazi verileri içeren DU verileri PSO kullanılarak [2], [38]- [40] ve DAÖ verileri de GA kullanılarak [41]- [43] model parametre kestirimleri yapılmıştır. İki boyutlu (2B) örnek için sentetik (yapay) karşılıklı kuyu GPR verisi YIİ ve doğrusallaştırılmış, yuvarlatma kısıtlı en küçük kareler algoritmalarının kullanıldığı sıralı melez (hibrit) tomografik ters çözüm yaklaşımıyla modellenerek iki kuyu arasındaki radar hız dağılımı saptanmıştır [44].…”

Investigating fracture-crack systems with geophysical methods in Bayburt Kiratlı travertine

“…For example, the algorithm yields solutions not dependent on an initial model, and it is also successful in avoiding becoming trapped in local mmimums. Concurrently, a 2D interpretation of the data set was achieved by a linearized least-squares algorithm that yielded an image of the subsurface, including lateral resistivity changes [15].…”