Reflection Seismic Data Along Orsa Profile Case Study

Reflection seismic data along Orsa profile was acquired in 2011 (Fig. 2) by Juhlin et al. (2012). The length of the profile was 12 km directed by NE-SW direction. The acquisition line is crooked for the purpose of the facility. and followed roads and forest due to crooked line. The general acquisition parameters list in Table 1. Table 1 list the data acquisition along the profile. The VIBSIST 3000 was used as a source to generate the seismic signal with 542 points and 20 m source spacing. The spread type was used in the seismic survey and SERCEL 428UL instrument for recording. In total about 320 active channels were used with a nominal CDP fold of 80. The data processing relatively showed good image along the profile special northern part.
Prior to stacking the data, aseries of constant velocity stacks were generated ranging from 3000 m/s to 6000 m/s with 200 m/s increment. The velocity analysis step was more important to improve the seismic image. Figure ( ) show the compare between the previous unmigrated section and re-processing unmigrated section. For comparison, the previously migrated stack and the re-processed migrated stack are shown in Fig. ( ). So the reflections in re-processing section be more clear and
The gravity data were reduced to datum following the standard data reduction procedure. So we were employing drift correction, tidal correction, free-air correction, bouguer correction and terrain correction to obtain the subsurface mass effect only (Fig. ). The most important step in processing is separation of the regional field, which result from deep structures, from those due to shallow sources (residual field) prior to the interpretation of magnetic and gravity data (El-Batroukh and Zentani, 1980; Xu et al., 2009; Cella and Fedi, 2012). There are three main methods for separating the regional field: graphical, spectral and polynomial fitting (Nettleton, 1976). In this study the quadratic polynomial used to calculate the regional field, than we direct subtract it from the bouguare value to achieve residual anomaly, which theoretically are related to the local geological structures (Fig. 5). The principle of the polynomial fitting method is that a polynomial surface is fitted to the measured data points, and any perversion of the measurement points from that surface is considered as a residual anomaly (Rao et al., 1975). In this study we apply 2D forward modeling approach for bouguare and magnetic anomaly along the seismic profile by using ModelVison software (Encom Technology)