Publications

There were some problems with seismic tomographic reconstruction when the Low Velocity Layer (LVL) exists at the top of the investigation area. Consequently, a new technique has been introduced to improved the tomographic image. It is based on the downward continuation principle. The presence of the LVL is known as determined by the refraction seismic method. The knowledge of the thickness of the LVL and the top of bedrock enables us to place 'virtual receiver' andlor 'virtual source' in appropriate places by the raytracing methodology. The use of the downward continuation principle by locating the 'source' and/or 'receiver' below the LVL can maximize reconstruction and reduce the effects of the LVL on tomography image reconstruction.To learn more about the capability of this methodology, four tomographic algorithms were tested through synthetic studies, i.e. Back Projection Technique (BPT), Iterative Least Square Technique (ILST), Simultaneous Iterative Reconstruction Technique (SIRT), and Modified Simultaneous Iterative Reconstruction Technique (MSIRT). The last technique called 'Modified SIRT' was originally proposed by Sanny and Sassa (1995) and Sanny and Sassa (1996). We can improved the image by those various tomographic methodologies. In our synthetic model, results from the ILST, SIRT, and Modified SIRT methods show improvement of the image and high performance in accuracy and resolution.