Analisis Kuantitatif pada Data VLF-EM Menggunakan Metode Inversi 2D (Studi Kasus Kawasan Karst Donorojo, Pacitan)

Rochmah, Khusnul Nur (2023) Analisis Kuantitatif pada Data VLF-EM Menggunakan Metode Inversi 2D (Studi Kasus Kawasan Karst Donorojo, Pacitan). Other thesis, Institut Teknologi Sepulu Nopember.

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Abstract

Metode very low frequency-electromagnetic (VLF-EM) merupakan salah satu metode geofisika yang dapat mengidentifikasi bawah permukaan berdasarkan distribusi resistivitas dan konduktivitas. Metode ini menggunakan transmitter pada frekuensi 15–25 kHz, yang memungkinkan penetrasi kedalaman yang cukup dalam pendugaan sungai bawah permukaan di daerah Karst. Penelitian ini difokuskan pada analisis distribusi nilai resistivitas pada penampang 2D bawah permukaan hasil inversi data VLF-EM untuk pemetaan sungai bawah permukaan. Pengukuran VLF-EM dilakukan di Desa Cemeng dan Desa Klepu dengan panjang lintasan berkisar 200–450 m, jarak spasi pengukuran 5 meter, dan frekuensi pengukuran 19800 Hz. Data lapangan yang diukur terdiri dari data tilt-angle, elips, Hver, dan Hhor. Pengolahan data dilakukan secara kualitatif yaitu filter Fraser, Karous Hjelt dan kuantitatif yaitu inversi. Interpretasi kuantitatif data VLF-EM dilakukan dengan mengkorelasikan hasil kualitatif dan kondisi geologi sehingga interpretasi lebih tepat dan akurat. Hasil pengolahan kuantitatif menunjukkan bahwa model inversi akurat dalam menunjukkan daerah anomali konduktif berdasarkan distribusi nilai resistivitas bawah permukaan. Interpretasi data kuantitatif menunjukkan nilai resistivitas rendah berkisar dari 0–500 Ωm yang diduga sebagai sungai bawah permukaan teridentifikasi pada lintasan 1 sampai lintasan 4. Anomali sungai bawah permukaan pada lintasan 1 terletak pada jarak 100–150 m kedalaman 0–25 m, lintasan 2 pada jarak 70–90 m kedalaman 0–20 m, lintasan 3 pada jarak 105–145 m kedalaman 0–30 m, jarak 250–280 m kedalaman 0–10 m, serta jarak 330–350 m kedalaman 0–20 m, dan lintasan 4 pada jarak 85–115 m kedalaman 0–20 m, serta jarak 160–180 m kedalaman 0–20 m.
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The very low frequency-electromagnetic (VLF-EM) method is a geophysical method that can identify the subsurface based on resistivity and conductivity distributions. This method uses a transmitter at 15-25 kHz frequency, which allows sufficient depth penetration to estimate underground rivers in Karst areas. This research is focused on analyzing the distribution of resistivity values in 2D subsurface cross-sections resulting from the inversion of VLF-EM data for underground river mapping. VLF-EM measurements in Cemeng and Klepu Village, with a track length ranging from 200-450 m, with 5 meters spacing, and a measurement frequency of 19800 Hz. The measured field data consist of the tilt angle, ellipse, Hver, and Hhor data. Data processing was carried out qualitative using Fraser, Karous Hjelt filters, and quantitatively using inversion. Quantitative interpretation of VLF-EM data then correlated with qualitative results and geological conditions, so the interpretations are more precise and accurate. The quantitative processing results show that the inversion model is accurate in showing conductive anomalies area based on the distribution of subsurface resistivity values. Quantitative data interpretation shows low resistivity values ranging from 0-500 Ωm which are identified as underground rivers in Line 1 to Line 4. The underground river anomaly on Line 1 is located at a distance of 100-150 m depth 0-25 m, Line 2 at a distance of 70-90 m depth 0-20 m, Line 3 at a distance of 105-145 m depth 0-30 m, a distance of 250-280 m depth 0-10 m, and a distance of 330-350 m depth 0-20 m, and Line 4 at a distance of 85-115 m depth 0-20 m, and a distance of 160-180 m depth 0-20 m.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Analisis Kuantitatif, Sungai Bawah Permukaan, Quantitative Analysis, Underground River, VLF-EM
Subjects:	G Geography. Anthropology. Recreation > GB Physical geography > GB1003.2 Groundwater. G Geography. Anthropology. Recreation > GB Physical geography > GB600 Karst conservation.
Divisions:	Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Geophysics Engineering > 33201-(S1) Undergraduate Thesis
Depositing User:	Khusnul Nur Rochmah
Date Deposited:	29 Nov 2023 02:27
Last Modified:	29 Nov 2023 02:27
URI:	http://repository.its.ac.id/id/eprint/103105

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