DETERMINATION OF S WAVE VELOCITY FROM SURFACE WAVES DATA BY F-K SPECTRUM ANALYSIS & DIFFERENTIAL EVOLUTION ALGORITHM INVERSION METHODS, CASE STUDY IN TANIKOTA AREA

• Main Author: RAMDHONI NIM: 12314042, SETYO
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/30894
• Institution: Institut Teknologi Bandung

<p align="justify">One of the methods which use surface waves to determine the S wave velocity of subsurface is Multichannel Analysis of Surface Waves (MASW) method. This method consist of three steps such as acquisition, dispersion curve analysis, and inversion. Variation of data processing techniques for this method have been developed a lot. In this research, f-k transform method will be used in dispersion curve analysis and for the inversion, Differential Evolution algorithm (DE) will be applied. Those steps will be applied on data with FKSW & DEISW program which developed by author. Syntethic data are used to measure accuracy level of the method. Result of syntethic data test show that DE inversion method is good enough to reconstruct syntethic model with variation of model parameters (four layers model, density variation, up to low velocity layer model) and noise variation up to 20%. Then, this methods will be applied on field data from acquistion in Tanikota area, side of Cikapundung river, with variation of source position & geophone space. The result from f-k spectrum analysis of observed data show that for Tanikota area, the optimum source position and geophone space with 10lb sledgehammer source are source with offset below 10m and geophone space 1m. Result from observed data inversion which use optimum acquisition parameter tell the existance of 3 layer below the surface which interpreted as soil for first layer (thickness 0.9m & S-waves velocity (Vs) 84.1m/s), saturated clay for second layer (thickness 4.8m & Vs 534.1m/s) and tuff-volcanic breccia for third layer (Vs 1245.7m/s). This result similar with geological field and refraction sesimic data.<p align="justify">