Shalihah, Anissa Avickry (2025) Analisis Kecepatan Gelombang Geser Menggunakan Metode Spatial Autocorrelation Dengan Konfigurasi Segilima Di Wilayah Institut Teknologi Sepuluh Nopember Surabaya. Other thesis, Institut Teknologi Sepuluh Nopember.
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Abstract
Surabaya merupakan salah satu kota besar di Indonesia yang secara geografis dilewati oleh dua sesar aktif, yaitu Sesar Waru dan Sesar Surabaya. Menurut PuSGeN, 2017, kedua sesar tersebut memiliki potensi dapat menimbulkan gempa bumi dengan magnitudo mencapai 6,5 SR yang dapat menyebabkan kerusakan ringan hingga berat tergantung kedalamannya. Institut Teknologi Sepuluh Nopember (ITS) yang berlokasi di Keputih, Kecamatan Sukolilo, Kota Surabaya, termasuk dalam wilayah yang rawan secara seismik karena berada di dekat jalur sesar dan memiliki kondisi tanah dominan berupa aluvial yang rentan terhadap amplifikasi gempa. Dengan mempertimbangkan faktor geologi dan geografis tersebut, perlu dilakukan kajian mikrozonasi seismik karakteristik bawah permukaan di wilayah kampus ITS. Penelitian ini menggunakan metode Spatial Autocorrelation (SPAC) untuk menganalisis data mikrotremor dan memperoleh kurva dispersi gelombang Rayleigh. Akuisisi data dilakukan di 20 titik menggunakan konfigurasi segilima dan geophone berfrekuensi 10 Hz dengan bantuan perangkat lunak STnet. Data mikrotremor yang diperoleh kemudian diolah menggunakan perangkat lunak Geopsy, HVinv, Surfer, dan overlay pada Google Earth. Hasil pengolahan dan analisis menunjukkan kurva dispersi pada rentang kecepatan fase 70 m/s - 243,30 m/s dan frekuensi berada pada rentang 2 Hz -13 Hz. Didapatkan juga best model nilai kecepatan gelombang geser (Vs) dan kedalaman pada tiga lapisan tanah di 20 titik observasi. Lapisan pertama diperoleh rentang nilai Vs berkisar 70.07 m/s - 99.95 m/s dengan kedalaman lapisan berkisar 1.17 m - 4.99 m , lapisan kedua diperoleh rentang nilai Vs berkisar 85.35 m/s – 137.71 m/s dengan kedalaman berkisar 5,1 hingga 9,9 m, dan lapisan ketiga (halfspace) diperoleh rentang nilai Vs berkisar 190,15 m/s – 457,13 m/s. Model terbaik tersebut kemudian divisualisasikan dalam bentuk peta kontur 2D, 3D, overlay pada peta wilayah ITS dan profil kontur kecepatan gelombang geser terhadap kedalaman bawah permukaan. Berdasarkan analisis nilai Vs, lapisan pertama dan kedua diperkirakan menurut standar internasional dalam klasifikasi tanah lunak (kelas E: < 175 m/s), sedangkan lapisan ketiga diperkirakan menurut standar internasional sebagai tanah sedang (kelas D: 175–350 m/s) hingga tanah keras sangat padat (kelas C: 350–750 m/s). Ketidakakuratan di beberapa titik lokasi disebabkan gangguan lingkungan saat proses akuisisi data seperti aktivitas mahasiswa, kepadatan penduduk, noise urban, serta kesalahan dalam pemasangan geophone yang tidak rata atau miring. Pantulan gelombang oleh struktur bangunan di area urban juga menyebabkan tumpang tindih sinyal, khususnya pada frekuensi tinggi, yang sulit dihilangkan meskipun telah dilakukan proses filtering.
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Surabaya is one of the major cities in Indonesia that is geographically traversed by two active faults, namely the Waru Fault and the Surabaya Fault. According to PuSGeN (2017), both faults have the potential to generate earthquakes with magnitudes reaching up to 6.5 on the Richter scale, which can cause light to severe damage depending on the depth. The Institut Teknologi Sepuluh Nopember (ITS), located in Keputih, Sukolilo District, Surabaya, is considered a seismically vulnerable area due to its proximity to the fault lines and its predominantly alluvial soil, which is highly susceptible to seismic wave amplification. Considering these geological and geographical factors, a seismic microzonation study is essential to evaluate the subsurface characteristics of the ITS campus area. This study employs the Spatial Autocorrelation (SPAC) method to analyze microtremor data and extract Rayleigh wave dispersion curves. Data acquisition was carried out at 20 locations using a pentagonal array configuration and 10 Hz geophones, assisted by the STnet software. The recorded microtremor data were processed using Geopsy, HVinv, and Surfer software and visualized through Google Earth overlay. The analysis results show that the dispersion curves fall within a phase velocity range of 70 m/s to 243.30 m/s and a frequency range of 2 Hz to 13 Hz. The inversion process produced best-fit models for shear wave velocity (Vs) and layer thickness at three soil layers across the 20 observation points. The first layer showed Vs values ranging from 70.07 m/s to 99.95 m/s with depths between 1.17 m and 4.99 m; the second layer ranged from 85.35 m/s to 137.71 m/s with depths from approximately 5.1 m to 9.9 m; and the third layer (halfspace) exhibited Vs values from 190.15 m/s to 457.13 m/s.These models were visualized in the form of 2D and 3D contour maps, overlay maps of the ITS area, and shear wave velocity-depth profiles. Based on the Vs values and international standards for soil classification (e.g., NEHRP/VS30), the first and second layers are categorized as soft soil (Class E: Vs < 175 m/s), while the third layer falls into the classification of stiff soil (Class D: 175–350 m/s) to very dense soil or shallow bedrock (Class C: 350–750 m/s). Inaccuracies at certain locations are attributed to environmental disturbances during data acquisition, such as student activities, high population density, urban noise, and improper geophone placement (uneven or tilted). Wave reflections from buildings in urban areas also caused signal overlapping, particularly at high frequencies, which could not be completely eliminated despite filtering processes.
| Item Type: | Thesis (Other) |
|---|---|
| Uncontrolled Keywords: | Kecepatan Gelombang Geser, Kurva Dispersi, Mikrotremor, Peta Kontur, SPAC, Shear Wave Velocity, Dispersion Curve, Microtremor, Contour Map, SPAC |
| Subjects: | Q Science > QE Geology Q Science > QE Geology > QE538.5 Seismic tomography; Seismic waves. Elastic waves |
| Divisions: | Faculty of Science and Data Analytics (SCIENTICS) > Physics > 45201-(S1) Undergraduate Thesis |
| Depositing User: | Anissa Avickry Shalihah |
| Date Deposited: | 25 Jul 2025 08:22 |
| Last Modified: | 25 Jul 2025 08:22 |
| URI: | http://repository.its.ac.id/id/eprint/121589 |
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