Telah dilakukan pengukuran dengan metode magnetik untuk mengetahui struktur bawah permukaan di sekitar gunung kelud. Pengambilan data dilakukan secara acak pada area seluas 0,6 km x 1 km dengan jumlah titik yang diperoleh 244 titik ukur. Proses akusisi dilakukan dengan menggunakan Magnetometer Proton ENVI SCINTREX. Pengolahan data diawali dengan koreksi IGRF dan koreksi variasi harian untuk mendapatkan anomali medan magnet total. Kemudian reduksi bidang datar, kontinuasi ke atas pada ketinggian 100 meter hingga 400 meter di atas sferoida referensi dan hasilnya digunakan untuk pemisahan anomali lokal dan regional. Hasil interpretasi kualitatif menunjukkan adanya anomali dipole magnetik di sebelah timur yang membentang dari arah barat laut ke tenggara sebesar -2125 nT hingga 1863 nT. Metode Talwani 2-D digunakan untuk interpretasi kuantitatif. Model geologi yang dihasilkan adalah patahan atau sesar. Nilai suseptibilitas magnetik di bawah kubah kawah gunung kelud sampai ke gunung lirang (k=0,0124 emu/gram) didominasi batuan basalt, dan di gunung sumbing (k=0,0234 emu/gram – 0,0239 emu/gram) yang didominasi batuan andesit.

Ground Penetrating Radar (GPR) is a geophysical method used to identification subsurface condition at a certain depth, using a source of electromagnetic waves in the form of radar. Geoscanners Akula A9000C and Antenna Gecko 60 with 60 MHz antenna frequency were used for data acquisition for this study. Survey data was conducted as many four lines, located on the south and east sides of the lake, with the distance range from 0 to 145 m. This paper reports basic signal processing GPR data using matGPR for the analysis and modelling. The results show that there is anomaly which is suspected as water seepage appear on depth of 2 m. On the lengthwise line, anomalies show on a distance of 20 m and 35 m (line A) and 125 m and 135 m (line B), while on the crosswise line anomalies show on a distance of 35 m and 50 m (line C), 25 m and 95 m (line D). Water seepage can be found in this area as it is formed by alluvial depositional environment, remembering that the characteristics and rocks lithology in this area can stimulate water infiltration process. Water seepage will cause erosion of the lake and can collapse the lake’s structure.

The Ground Penetrating Radar (GPR) method commonly known as Georadar, a nondestructive geophysical method that uses electromagnetic waves. This method is widely used to determine conditions under the surface such as mapping structures and subsurface lithology or buried objects. In this study, the GPR measurement using Geoscanners AKULA A9000 + Antenna GCB3070 is conducted to detect the presence or capacity of a septic tank. The GPR data were initially processed using matGPR based on MATLAB. GPR data on each measuring line is processed first, a series of filters and gaining have been conducted such as Adjust Signal Position, Remove DC, Dewow, Inverse Amplitude Decay, Remove Global Background, Karhunen-Loeve Filter, then time to depth conversion with adjusted parameters. From the result of parameter analysis in processing data, found that the GPR data can be interpreted which show the underground septic tank in the study area with the presence of diffraction signatures.

The geoelectric method is a geophysical method based on the resistivity value of the material. The resistivity value gives an overview of the structure found at the observation site. The electrode configurations used are the Dipole-Dipole, Wenner-Alpha, Wenner-Schlumberger, and Pole-Dipole. The analytical measurement was carried out in the lake body with a track length of 48 meters. From the measurement results, we obtained a seepage of water in the lake body with a resistivity value <5 Ohmmeters. The observation site is dominated by clay type structure, which is found almost in all of the results of the geoelectric electrode configuration. Based on the results of the structural overview shows that the type of electrode configuration has advantages and disadvantages. The Wenner-Schlumberger configuration is very detailed with per layer structure and distribution but has the longest measurement time. Dipole-Dipole configuration has the advantage of being very sensitive to changes in vertical structure and the fastest measurement time, but not very good in horizontal structures. The Wenner-Alpha method is very sensitive to horizontal structural changes and has a moderate measurement time, but less sensitive to vertical structure changes. The pole-dipole configuration has a fast time and a moderate level of sensitivity at shallow depth. Based on the results, the Dipole-Dipole method is highly recommended because of the fast measurement time and the position of seepage can be found easier than the other methods.

Indonesia is a country that often experiences natural disasters as it is a meeting point of several tectonic plates. When a natural disaster occurs, most of the time the evacuation team having some trouble finding the buried victims underground. The Ground-Penetrating Radar (GPR) method is one of the solutions for this problem. GPR or also called georadar is a geophysical method that is used to investigate conditions under the earth’s surface using electromagnetic waves. This study aims to detect buried human bodies underground using the GPR method to increase the effectiveness and efficiency of natural disaster victims by doing a simulation measurement. It took place in one of the public cemeteries in Jakarta, Indonesia passing two graves with corpses buried around three years before the survey. GPR measurements were conducted using Geoscanners AKULA A9000+ Antenna GCB3070 to detect the buried human bodies underground. The GPR data then processed using MATLAB based program called matGPR. A series of adjustments and filters such as signal position adjustment, remove DC, mean filter, inverse amplitude decay, remove global background, and Karhunen-Loeve (KL) filter have been applied to the data. The result of data processing shows amplitude contrasts which are suspected to be the buried corpses. Further research can be conducted to investigate the buried victims from landslides, earthquakes, and other natural disasters.