Electronic Theses and Dissertation

Desa Neuheun, Kabupaten Aceh Besar, merupakan kawasan perbukitan dengan kondisi geologi vulkanik dan kemiringan lereng yang berpotensi mengalami ketidakstabilan. Permasalahan utama di lokasi penelitian adalah belum tersedianya informasi mengenai kondisi bawah permukaan dan persebaran zona lemah. Penelitian ini bertujuan menentukan nilai kecepatan gelombang geser (Vs), menginterpretasikan karakteristik lapisan bawah permukaan, serta mengidentifikasi zona lemah yang berpotensi mengalami longsor berdasarkan distribusi nilai Vs dan kondisi kemiringan lereng. Pengukuran dilakukan menggunakan metode Multichannel Analysis of Surface Waves (MASW) pada empat lintasan yang masing-masing memiliki panjang 69 m. Setiap lintasan menggunakan 24 geofon dengan spasi 3 m dan tujuh titik tembak. Data dianalisis melalui transformasi dari domain waktu ke domain frekuensi, analisis spektrum, pemilihan kurva dispersi, dan proses inversi untuk memperoleh profil Vs satu dimensi. Profil tersebut kemudian digabungkan menjadi penampang Vs dua dimensi hingga kedalaman investigasi sekitar 35 m. Hasil penelitian menunjukkan bahwa nilai Vs cenderung meningkat seiring bertambahnya kedalaman. Nilai Vs pada lintasan 1 berkisar 380–1250 m/s, lintasan 2 sebesar 210–1400 m/s, lintasan 3 sebesar 420–1170 m/s, dan lintasan 4 sebesar 410–1150 m/s. Lapisan dangkal diinterpretasikan sebagai lempung relatif lunak hingga relatif padat, sedangkan lapisan yang lebih dalam diinterpretasikan sebagai tuf dan napal yang lebih kompak. Zona lemah dengan nilai Vs < 550 m/s teridentifikasi pada kedalaman sekitar 0–19 m di lintasan 1, 0–10 m di lintasan 2, 0–22 m di lintasan 3, dan 0–20 m di lintasan 4. Berdasarkan hasil tersebut, lintasan 1 dan lintasan 3 memiliki potensi ketidakstabilan lereng yang lebih tinggi karena zona lemahnya berada pada lereng yang tergolong curam. Temuan ini dapat digunakan sebagai informasi awal dalam upaya mitigasi longsor di lokasi penelitian.

Kata kunci: kecepatan gelombang geser, MASW, zona lemah, longsor, kemiringan lereng

Neuheun Village, Aceh Besar Regency, is a hilly area characterized by volcanic geological conditions and slope gradients that may contribute to slope instability. The main problem at the study site is the limited availability of information regarding subsurface conditions and the distribution of weak zones. This study aimed to determine shear-wave velocity (Vs) values, interpret subsurface layer characteristics, and identify weak zones potentially associated with landslides based on the distribution of Vs values and slope conditions. Measurements were conducted using the Multichannel Analysis of Surface Waves (MASW) method along four survey lines, each 69 m in length. Each line consisted of 24 geophones with a spacing of 3 m and seven shot points. The data were processed through transformation from the time domain to the frequency domain, spectral analysis, dispersion-curve picking, and inversion to obtain one-dimensional Vs profiles. These profiles were subsequently combined to produce two-dimensional Vs cross-sections to an investigation depth of approximately 35 m. The results showed that Vs values generally increased with increasing depth. The Vs values ranged from 380 to 1,250 m/s along Line 1, 210 to 1,400 m/s along Line 2, 420 to 1,170 m/s along Line 3, and 410 to 1,150 m/s along Line 4. The shallow layers were interpreted as relatively soft to relatively dense clay, whereas the deeper layers were interpreted as more compact tuff and marl. Weak zones characterized by Vs values below 550 m/s were identified at depths of approximately 0–19 m along Line 1, 0–10 m along Line 2, 0–22 m along Line 3, and 0–20 m along Line 4. Based on these findings, Lines 1 and 3 exhibit a higher potential for slope instability because their weak zones are located on relatively steep slopes. These findings can serve as preliminary information for landslide mitigation efforts at the study site. Keywords: MASW, shear-wave velocity, weak zone, landslide, slope gradient