APPLICATION OF TRAVELTIME TOMOGRAPHY TO IDENTIFIED SHALLOW VELOCITY STRUCTURE USING 2-D SEISMIC LAND DATA

• Main Author: SATRIA WICAKSANA A. - NIM : 22314305, RADEN
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/30094
• Institution: Institut Teknologi Bandung

<p align="justify">2-D seismic refraction survey generally used to know the condition of shallow subsurface. In this method, the first arrival of waves at each receivers are used as input. These data can be processed by either seismic refraction method, or traveltime seismic tomography. In this study, traveltime tomography will be conducted using seismic refraction data consist of 13 points of sources and 24 points of receiver that installed at the surface, with hope that shallow velocity structure can be identified relatively detail. <br /> <br /> <br /> According to convensional refraction method with Generalized Reciprocal Method (GRM), the refractor can be known at depth of 7 – 8 m with higher (1482,14 m/s) lower layer velocity compared to the upper part (561 m/s). Checkerboard resolution test is performed with different grid and anomaly parameters to know the resolution of tomography using real data. All modeling are done using program package of First Arrival Seismic Tomography (FAST) which operated at Linux system operation. <br /> <br /> <br /> Results from resolution tests showed the smallest anomaly that can be resolved is 3×3 m using a grid of 1×1 m. This program is consist of forward modelling using eikonal-solver with finite difference and regularized inversion for the inverse modelling. The advantage of this method compred to others are the possibility to run inversion despite the fact that the number of known data (312 traveltimes) are much less dan the sought model parameters (7600 total grids). The resulting inversion parameters then used as the parameters for real data inversion. Final model tomogram showed two layers at 0 – 15 m depth range with subsurface velocity (200 – 1700 m/s) in each grids. The refractor depth of 5 – 8 m agrees with GRM’s result. <p align="justify"> <br />