Exploration for a cave by magnetic and electrical resistivity surveys: Ayvacik Sinkhole example, Bozdag, Izmir (western Turkey)

BALKAYA Ç., Gokturkler G., Erhan Z., Ekinci Y. L.

GEOPHYSICS, cilt.77, sa.3, 2012 (SCI İndekslerine Giren Dergi) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 77 Konu: 3
  • Basım Tarihi: 2012
  • Doi Numarası: 10.1190/geo2011-0290.1
  • Dergi Adı: GEOPHYSICS


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 Ayvacik 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 ID 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 (>316 Omega m), (2) an approximately 25-m-thick alluvial fill (100-316 Omega m), and (3) a limestone unit (316-3162 Omega m); and also suggested the existence of a high-resistive anomaly (>15000 Omega m), possibly a karstic cave, located at the depth of approximately 40 in. 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.