ESTIMATION OF S-WAVE VELOCITY 1D PROFILE FROM RAYLEIGH WAVE DATA USING FREQUENCY DECOMPOSITION-SLANT STACKING METHOD AND PARTICLE SWARM OPTIMIZATION INVERSION: TANI KOTA CASE STUDY

• Main Author: Julia Mardhiyah, Ferina
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/37162
• Institution: Institut Teknologi Bandung

Multichannel Analysis of Surface Waves (MASW) method used the dispersive characteristic of surface wave to identify layer below surface. MASW method procedure could be divided into three steps, those are data acquisition, dispersion curve extraction, and dispersion curve inversion. Data acquisition implementation really depends on the desired target. Various methods could be used in dispersion curve extraction step, one of them is frequency decomposition-slant stacking method. Extracted dispersion curve is then inversed to obtain the velocity profile of S-wave. Particle Swarm Optimization (PSO) inversion which is used the global optimization technique in solving the inversion equation could be used to do the dispersion curve inversion. Dispersion curve extraction and inversion applied to synthetic data and field data obtained from field acquisition in Tani Kota, Bandung. Frequency decomposition-slant stacking method test over synthetic data yields a good result, but over field data there is maximum amplitude trend with poor image because of noise. PSO inversion test over synthetic noise free data succeed to reconstruct up to three layers, including low velocity layer (LVL) existence, and noise variation up to 5%. Field data inversion result shows there are three layers under the surface interpreted as soil for first layer (thickness 1,2 m and S-wave velocity (Vs) 23,32 m/s), as saturated clay for second layer (thickness 3,89 m and Vs 605,59 m/s), and as tuff-volcanic breccia for third layer (Vs 1059,24 m/s). This interpretation of the inversion result matches the acquired geologic field data.