Integrasi Metode Resistivitas, Seismik Refraksi, Geologi Berbasis Geospasial untuk Identifikasi Potensi Longsor di Srimartani, Yogyakarta

Kabupaten Bantul merupakan salah satu kabupaten yang berpotensi terjadi tanah longsor, tepatnya di daerah Srimartani, Kecamatan Piyungan. Penelitian ini dilakukan dengan tujuan untuk mendapatkan data dan informasi mengenai parameter metode geofisika daerah longsor dan mengetahui dugaan zona potensi longsor. Metode yang digunakan dalam penelitian ini adalah survei lokasi, akuisisi metode seismik refraksi, akuisisi metode resistivitas, dan pemetaan foto udara (geospasial). Dari penampang bawah permukaan seismik refraksi metode hagiwara didapatkan bahwa lapisan lapuk pada daerah riset berupa soil dan pasir tuffan dikarenakan memiliki sifat permeable dan bidang gelincirnya yang bersifat impermeable. Pada penampang bawah metode seismik refraksi lapisan pertama yaitu soil dengan kecepatan V1 sekitar 313.8 m/s – 461.6 m/s dan lapisan kedua yaitu pasir dengan kecepatan V2 sekitar 459 m/s – 1567 m/s. Sementara penampang bawah permukaan metode resistivitas konfigurasi dipole – dipole didapatkan lapisan lapuk tersebut memiliki nilai resitivitas yang kecil dikarenakan lapisan tersebut bersifat lunak sehingga ada kemungkinan lapisan tersebut dalam kondisi basah. Pada penampang resistivitas memiliki nilai 126 ohm.m hingga lebih dari 301 ohm.m, daerah tersebut diperkirakan terdapat batuan breksi batuapung dari formasi semilir yang diduga sebagai bidang gelincir. Dari segi geologi, daerah penelitian sangat rentan terjadi tanah longsor dikarenakan kondisi lereng searah dengan kondisi struktur regional di daerah penelitian yaitu barat-timur, didukung oleh kondisi batuan yang ada berupa breksi batuapung dan tuff yang sangat rawan terjadi longsor. Dengan adanya penelitian ini, diharapkan dapat menambah pengetahuan mengenai antisipasi masyarakat dalam meminimalisir dampak yang ditimbulkan dari adanya tanah longsor. Bantul Regency is one of the districts that have the potential for landslides to occur, precisely in the Srimartani area, Piyungan District. This research was conducted with the aim of obtaining data and information about the parameters of the geophysical method of landslide areas and knowing the alleged landslide potential zone. The methods used in this research are site survey, seismic refraction acquisition method, resistivity method acquisition, and aerial photography (geospatial) mapping. From the subsurface seismic refraction of the Hagiwara method, it was found that the weathered layer in the research area was soil and sand due to its permeable properties and impermeable slip plane. . In the lower section of the seismic refraction method, the first layer is soil with a V1 velocity of around 313.8 m/s – 461.6 m/s and the second layer is sand with a V2 velocity of about 459 m/s – 1567 m/s. While the subsurface resistivity method of the dipole - dipole configuration found that the weathered layer has a small resistivity value because the layer is soft so there is a possibility that the layer is in a wet conditionIn the cross section resistivity has a value of 126 ohm.m to more than 301 ohm.m, the area is estimated to contain pumice breccia from the breccia formation which is thought to be a slip plane. In terms of geology, the research area is very susceptible to landslides because the slope conditions are in line with the regional structural conditions in the research area, namely west-east, supported by the existing rock conditions in the form of pumice breccia and tuff which are very prone to landslides. With this research, it is hoped that it can increase knowledge about community anticipation in minimizing the impact of landslides.

Identification of zeolite using electrical resistivity tomography in Campang Tiga, South Lampung Regency

Currently, zeolites are widely used in various fields including horticultural, agricultural, household, industrial, water and wastewater management. Due to the increasing use of zeolites, it is estimated that the demand for zeolites will increase in the future. Therefore, it is necessary to conduct a survey to determine the potential of zeolites in an area. Campang Tiga is an area with quite a lot of potential zeolite and is exposed on the surface along with tuffs from the Lampung Formation. To estimate the potential zeolite in this area, it was carried out the Electrical Resistivity (ERT) measurements to determine the distribution and depth of the tuff layer associated with the zeolite. Measurements were made in 3 lines with an electrode spacing of 6 m using a dipole-dipole configuration. The result performs that the zeolites in the area are located at a depth of up to ∼ 10 m and are getting thicker towards the east until they reach a depth of ∼ 20 m. The results of this interpretation have been combined with the results of laboratory measurements of the resistivity value of zeolites in the area. Laboratory test results present that the zeolite resistivity value ranges from 20-300 Ωm.

Laboratory-scaled Azimuthal Resistivity Survey for Fracture Detection

We conducted azimuthal resistivity survey (ARS) at laboratory scale to study apparent resistivity patterns due to fracture existing in subsurface through physical modeling using test objects buried in a sandbox as well as in a test location outside laboratory building. This survey was divided into 2 experiments, i.e. experiment A and experiment B. In experiment A the survey is implemented on 2.50 m x 1.5 m x 0.81 m sandbox, made of 10mm thick glass plates. Sandstone was used as medium representing quasi homogenous medium. Clay roof tiles as well as steel plates as test objects were buried in the sandbox with three different deep angles: 90°, 45° and 0°. In experiment B this survey was conducted outside laboratory building on the grass field and implemented on 2.50 m x 2.5 m x 1.0 m soil body. Vertical single glass plate as well as vertical double glass plates at 30 cm distance were buried in the soil body. Azimuthal resistivity measurements at 15° angular step using Wenner and dipole-dipole configuration were carried out in both experiments located at 1 point just above anomalous object for experiment A and at 3 points at 15 cm distance from anomalous object for experiment B. As a compliment to ARS we acquired profiling data from two lines parallel and perpendicular to horizontal axis of anomalous object. Our results show that the apparent resistivity pattern can show the direction of anomalous object for both configurations and experiments with a little deviation.

Metode Geolistrik Konfigurasi Dipole-Dipole Untuk Penetapan Bidang Gelincir Gerakan Tanah di Jajaway, Palabuhanratu, Sukabumi

ABSTRAKGerakan tanah di kompleks perkantoran Kabupaten Sukabumi di Jajaway, Palabuhanratu, terjadi di luar perkiraan dan perencanaan pembangunan sebelumnya. Untuk melihat kondisi dan luasan daerah gerakan tanah dan dalam usaha mengurangi resiko kerugian lebih besar, diperlukan identifikasi bidang gelincir gerakan tanah di kompleks tersebut. Bidang gelincir dicari berdasarkan model tahanan jenis yang diperoleh dari survei pengukuran geolistrik. Akuisisi data dilakukan pada 7 lintasan, dengan 6 lintasan berarah utara-selatan dan 1 lintasan berarah barat-timur. Metode akusisi yang digunakan adalah tahanan jenis multielektrode dengan konfigurasi dipole-dipole. Hasil penelitian membuktikan bahwa kondisi perlapisan batuan lepas tetapi lebih berat di atas lapisan lempung merupakan salah satu penyebab kejadian pergerakan tanah. Kejadian itu sangat terlokalisir karena kondisi seperti itu tidak ditemukan pada lintasan lainnya.Kata kunci: bidang gelincir, geolistrik, gerakan tanah, konfigurasi dipole-dipole, tahanan jenisABSTRACTGround movement in the Sukabumi Regency office complex (Jajaway, Palabuhanratu), occurred unexpectedly. To reduce the potential risk, we need to identify the slip surface to detect the possibility of more landslides. The resistivity model by the dipole-dipole geoelectrical method was applied to find the slip surface. Data acquisition was carried out in 7 lines: 6 north-south lines and 1 east-west line. The resistivity models present the distribution of resistivity below the surface. Above this clay layer, there is a higher resistivity layer, which is related to sandy tuff and breccia. The condition might cause the previous creeping type of ground movement. The type of layering is not found in the other lines. Therefore we do not expect a similar ground movement would occur in those lines.Keywords: dipole-dipole configuration, geoelectrical, landslide, resistivity, slip surface

Stabilization Methodology in Foundation Soils by ERT-3D Application in Estepona, South Spain

The paper proposes a novel methodology for the stabilization of shallow foundations, with a simplified model combined with 3D electrical resistivity tomography (ERT-3D and consolidation injections. To determine its usefulness, the method has been applied in a case located in Estepona (southern Spain). The chosen tomography model is the dipole–dipole configuration, with an optimized distance between electrodes of 0.80 m for a better visualization of the foundation subsoil; with this parameterization, a total of 72 electrodes were installed in the analyzed case. In this work, the depth of the anomaly in the building’s supporting subsoil was detected ranging from 2.00 m to 3.90 m deep. The study also delineates areas of high resistivity variations (50–1000 Ω m) in the middle and eastern end of the field. These data have been validated and corroborated with a field campaign. The results of the ERT-3D monitoring are presented, once the investment data has been processed with the RES3DINV software, from the beginning to the end of the stabilization intervention. The novelty occurs with the interaction between the tomography and the foundation consolidation injections, until the final stabilization. This is a very useful methodology in case of emergency consolidation, where there is a need to minimize damage to the building. Thus, people using this combined system will be able to practically solve the initial anomalies of the subsoil that caused the damages, in a non-invasive way, considerably lowering the value of the resistivities.

Stabilization methodology in foundation soils by ERT-3D. Application in Estepona, South Spain.

The paper proposes a novel methodology for the stabilization of shallow foundations, with a simplified model combined with 3D Electrical resistivity tomography (ERT-3D) and conso- lidation injections. To determine its usefulness, the method has been applied in a case located in Estepona (southern Spain). The chosen tomography model is the dipole-dipole configuration, with an optimized distance between electrodes of 0.80 m for a better visualization of the foundation subsoil; with this parameterization, a total of 72 electrodes were installed in the analyzed case. In this work, the depth of the anomaly in the building's supporting subsoil was detected ranging from 2.00 m to 3.90 m deep. The study also delineates areas of high resistivity variations (50-1,000 Ω m) in the middle and eastern end of the field. These data have been validated and corroborated with a field campaign. The results of the ERT-3D monitoring are presented, once the investment data has been processed with the RES3DINV software, from the beginning to the end of the stabilization intervention. The novelty occurs with the interaction between the tomography and the foundation consolidation injections, until the final stabilization; very useful methodology in case of emergency consolidation, where there is a need to minimize damage to the building. Thus, people using this combined system; will be able to practically solve the initial anomalies of the subsoil that caused the damages, in a non-invasive way, considerably lowering the value of the resistivities.

The Estimation of Subsurface Structure within Geothermal Manifestation Area as an Outflow Zone Using Geoelectrical Resistivity Method in Tegal, Jawa Tengah

<p class="TesisTextOneHalfSpace"><em>Indonesia is one of the country having a lot of geothermal fields potentially used as a source of energy. For example, Java island is noted to have almost 57 geothermal fields. One of those geothermal fields which is rarely studied is Guci geothermal field. Hence, there was conducted a research to investigate the subsurface image and geothermal system in Guci geothermal field based on resistivity data. </em><em>The research in Guci geothermal field was carried out using geoelectrical method. Resistivity geoelectrical research used two configurations, namely dipole-dipole and schlumberger. Data acquisitions for dipole-dipole configuration was done in two lines, 500 metres spread for each line. Whereas the acquisitions for schlumberger configuration was done in four points, 200-250 metres spread for each point. </em><em>Research result showed that the area of geothermal manifestation in Guci consist of top soil layer, sandstone, andesite, and a fluids-containing layer. A fluids-containing layer is estimated to be related to geothermal manifestation in Guci and is a fault zone. Fault is estimated to be a normal fault and lies in 20 metres depth. Fault within geothermal manifestation area in Guci has a role as the pathway of hot-fluid out to the surface which forms a manifestation.</em></p>

Geoelectric Method Application of Dipole-Dipole Configuration for Identification of Landslide Prone Areas in Poka Village, Ambon

Landslide disaster is one type of disaster that often occurs in Indonesia which causes many casualties and loss of property. Ambon City is an area with high potential for landslides. This is because Ambon City is an area with steep slopes and high rainfall, so a study is needed to overcome this as a disaster mitigation effort. This study aims to determine the area of landslide slip and direction of landslides as a basis for identifying landslide-prone areas using the dipole-dipole configuration geoelectric method. This research was conducted in Poka Village, Ambon City, Maluku Province. Geoelectric measurements using the AGI Ministing tool with data retrieval as much as 5 tracks. Based on the results of the analysis, it was found that the soil layer was dominated by clay and limestone. The reconstruction results show that the topography of the area is a slope with a slope of 45o-80o, and the slip plane has each path with a resistivity contrast of ± 25-60 Ωm at a depth of 5-15 meters, while the direction of the landslide is directed to the southeast.