RAYLEIGH WAVE INVERSION TO OBTAIN S WAVE VELOCITY AND LAYER THICKNESS NEAR THE SURFACE USING THE MONTE CARLO METHOD

• Main Author: Setianda, Rizky
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/67024
• Institution: Institut Teknologi Bandung

In the characterization of near-surface rocks, the S wave velocity near the surface is very important to determine the strength of the rocks within it. Rayleigh waves are surface waves that travel along or near the ground surface. The phase velocity of the Rayleigh wave is a function of four parameters of the earth model: P wave velocity, S wave velocity, density and layer thickness. The dispersion curve is the frequency curve against the phase velocity of the Rayleigh wave. If the dispersion curve is inverted, it will get a profile of the S wave velocity with respect to the depth of the earth. This research aims to estimate the value of the S wave velocity and layer thickness near the surface by applying the Monte Carlo inversion to the Rayleigh wave dispersion curve with synthetic models and field data. The research data used are synthetic models and field data at positions A and B which have different acquisitions with the assumption of elastic media, isotropic media and the assumption of a half-space earth model. The research begins by testing the effectiveness of the Monte Carlo inversion in this research using a synthetic model and tested by various variations of the initial model (5%, 10%, 20%, 25%, 50%, 75%, 100%, 125%, 150% and 175% of the S wave velocity (????????) and layer thickness (????)), which it is known that the error of deviation from the true model, namely the synthetic model, is around 0-8%, it can be said that the Monte Carlo inversion in this research is not influenced by the initial model and it can also be said that the Monte Carlo inversion in this research is effective. Then, the Monte Carlo inversion modeling of this research was carried out on the Rayleigh wave dispersion curve of field data at positions A and B. Judging from the profile of the S wave velocity against the depth of the modeling results, it can be said that the field data at position A has 3 layers with the first layer having an S wave velocity of 58,427 m/s and a layer thickness of 1,470 m, then the second layer has an S wave velocity of 188,515 m/s and a layer thickness of 4,787 m and finally the third layer has an S wave velocity of 260,450 m/s and a layer thickness of infinite. While the field data at position B has 3 layers with the first layer having an S wave velocity of 63,094 m/s and a layer thickness of 1,729 m, then the second layer has an S wave velocity of 205,150 m/s and a layer thickness of 5,945 m and finally the third layer has an S wave velocity is 285.130 m/s and the layer thickness is infinite.