The seismic technique of wide angle (WAR) reflection-refraction, utilizing, in general, the air gun shots of the near vertical reflection profiles (NVR) and recording the wide angle arrivals at piggy back stations positioned onshore, is having an increasing role in crustal surveys, especially when exploring the transitional belts from continental to oceanic domains, in this introductory paper the objectives and problems of this type of survey are outlined as well as the experience collected during the last decade by the projects carried out in several coastal areas of the world. The major role of the offshore-onshore WAR surveys is to fill the gap beneath the coastal strip by connecting the land seismic profiles with the marine NVR lines. But also when other data are available, the WAR profiles with high density of traces are very profitable as complementary information, especially on the structure of the lower crust and Moho boundary. The activity of the Italian Group "SEA-LAND" is summarized while introducing the other papers of this volume; they deal with specific subjects, both on the used techniques and on the obtained results. It is pointed out that the main achievement of recording onshore the air gun shots during the fulfillement of the NVR marine profiles of the Italian project CROP, was to test the potential of the technique in different geological and environmental conditions. However, the results so far obtained already bring a valuable contribution to the interpretation of crustal structures that will be made sounder as soon as more constraints become available.

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