DOI: 10.23729/e163d50e-2553-483b-8ec0-26563ca29677
title: BABEL wide-angle refraction and reflection survey

description: The BABEL seismic experiment was conducted in September and October of 1989 in the Baltic Sea (BABEL Working Group 1993). Reflection seismic as well as wide-angle reflection and refraction data were acquired in a marine seismic survey resulting in 2,268 km of seismic measurement lines. The available data includes wide-angle recordings of marine air gun shots of lines 1, 3, 4 and 7 recorded at land stations in Finland and Sweden. Line 1 runs in southern Gulf of Bothnia and is oriented south to north. Line 7 is oriented west to east and crosses line 1 at the southern end. Both lines 1 and 7 transect the Åland rapakivi granites. Lines 3 and 4 are located in northern Gulf of Bothnia and transect the Skellefte district. Three velocity models are available of the BABEL lines. Modeling of lines 1 and 7 produced two separate models modeled by Heikkinen and Luosto (1992) and a single model of lines 3 and 4 was constructed by Komminaho and Yliniemi (1992). The models do not contain specific spatial coordinates, but instead only information about the velocity at certain depth and distance along the profile. This is because of the geometry of the wide-angle survey configuration. The marine shots were recorded by only a few land stations at large offsets from the original survey line. As the shots were not recorded along the line, the recordings do not represent the velocity structure along the survey line, but rather the midpoint of wide-angle reflections placed approximately in the middle between the line and the recording station. Each of the velocity models is composed of multiple land station recordings with different midpoints. This means that the models do not necessarily represent a continuous geographical line. More detailed explanation of the model positioning is provided by the original publications (Heikkinen and Luosto 1992, Komminaho and Yliniemi 1992, BABEL Working Group 1993). Wide-angle section data are available from the modeled lines (1, 3, 4 and 7) and some additional data from Finnish stations is available from lines 2, B and C. Each wide-angle section file of BABEL lines is from a single station with each marine shot presented as an individual trace. The unusual station geometry must be considered when using the data. The sections are in standard IBM SEG-Y format with separate files for P- and S-waves and stacked sections. More information of the data acquisition is provided by BABEL Working Group (1993). BABEL Working Group, 1993. Integrated Seismic Studies of the Baltic Shield Using Data in the Gulf of Bothnia Region. Geophysical Journal International 112: 305–324. Heikkinen, P. and U. Luosto, 1992. Velocity structure and reflectivity of the Proterozoic crust in the Bothnian Sea. In: The BABEL Project, First status report, 65–69, Commision Of The European Communities. Komminaho, K. and Yliniemi, J. 1992. Archaean and early proterozoic units around the northern Gulf of Bothnia: Interpretation of wide angle data from Finland. In: The BABEL Project, First status report, 51–53, Commision Of The European Communities.