Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
Reflection seismology is a geophysical exploration method that is used to estimate the physical properties of the earth. It is by far the most used and well-known geophysical technique and it has dominated the industry of oil and gas exploration since the beginning. Moreover, it is an important scientific tool for mapping and studying the subsurface structures. The predominance of the seismic reflection method over other geophysical techniques is a combined effect of high resolution, high accuracy and great penetration. Compared to other geophysical means, where the final result many times can look a little bit obscure, the resulting seismic section will be a direct image of the subsurface.
Seismic sections can be produced to reveal geological features on scales of metres to that of the whole lithosphere. The last 20 years the sophistication of the technique has improved considerably, much as a result of massive investments in its development made by the hydrocarbon industry, but also as a result of more accurate electronic and powerful computing technology.
The quality of the final seismic image is much dependent on the processing phase following the acquisition. For such a well tested method as reflection seismology a kind of step-by-step procedure has emerged over the years. Still, the geophysicists roll in the processing is critical since it is up to him or her to test and find the parameters that optimize the result in every single step.
The processed data comes from a large scale seismic survey (DACIA-PLAN) made in the south east of Romania. The purpose of the project was to map the geological structure under the eastern part of the Carpathians and the basins developed in the Vrancea zone, one of the most seismological active areas in Europe (Landers et al., 2003). As a result of extensive geophysical and geological projects this area is now quite well mapped. However, the exact cause of what triggers the earthquakes is still not fully understood and will probably generate further investigations of the area.
The data outputted from the DACIA-PLAN survey has been used in a number of scientific reports. In Panea et al., (2005) the data was processed to form two independent stacked sections. One containing data from the whole profile stacked to a depth of 20 s. The other section was processed from a subset of the DACIA-PLAN data, focusing on the upper 10 s of the Focsani Basin. Reason for doing two independent processing sequences was the decreasing quality of data obtained within and beneath the trust belt.
For this thesis processing was committed to a depth of 20 s for the whole seismic line, but both a full and partial stack are presented in chapter 6. Also a discussion and comparison with the result presented by Panea et al. (2005) follows in this chapter.
The main purpose with this thesis was to be familiar with the theory of reflection seismology and get to work with some of the typical steps, that are used in most processing sequences, and apply them on a real dataset. By reprocessing the DACIA-PLAN data the ambition was to improve the final seismic image, but also there was a hope to reveal some new information, particularly in the harsh area around the thrust belt.
2008. , 50 p.