Application of very low frequency (VLF) method in conductivity mapping aroud the Sileri Crater, Dieng Volcanic Complex, Central Java

Sileri Crater is a manifestation of the Dieng Volcanic Complex (DVC) which has a big geothermal prospect. The problem of subsurface conductivity distribution is very important in geothermal prospecting. The geothermal prospects indicated by the presence of manifestations that have characteristics of high conducivity values. The conductivity parameters were obtained by the electromagnetics Very Low Frequency (VLF) method. Research in DVC prospect area, precisely around theSileri Crater area using the VLF method, aims to map the subsurface structure through the distribution of conductivity values. VLF data consists of tilt, ellipse, vertical and horizontal magnetic field. VLF data processing is done by using the filter of moving average, Fraser and Karous- Hjelt. Current Density Equivalent (CDE) results are correlated to simplify the interpretation of the conductive zone. The results show that the conductive anomalies on A, B C, and D lines in the east are influenced by the presence of geothermal pipes around the crater. Other conductive anomalies found on the E and F lines are estimated to be caused by the influence of lithological contact between andesite lava and volcanic deposits. Andesite lava responds to conductive anomalies on the measurement results of the VLF method while volcanic deposits lithology has a more resistive.