T ransient, voluminous basaltic volcanism is frequently associated with continental breakup, forming so-called volcanic rifted continental margins. Until recently, most rifted margins were considered nonvolcanic; however, the improvement in seismic imaging techniques has shown that breakup volcanism is a common phenomenon. At the November 1997 Volcanic Margin Workshop in Potsdam, it was shown that at least 70% of the Atlantic margins are volcanic (a number which may apply to the Indian Ocean margins as well). The progress of exploration beyond the shelf edge into deep water and the fact that hydrocarbon reservoirs have been drilled in environments influenced by breakup vol- canism show the importance for the explorationist of understanding volcanic margin formation and its conse- quences for the hydrocarbon resource potential of the adja- cent basins. The constructional processes and petrophysical prop- erties of basaltic deposits are at least as complex as in any siliciclastic system. Images of basaltic constructions reveal large local and regional variations in seismic characteris- tics. Frequently, intrabasalt and subbasalt reflectivity is very poorly imaged. An improved imaging capability is crucial to address and resolve scientific problems and eco- nomic potential of volcanic provinces. Here, we focus on the seismic characterization of flood basalt constructions based on analysis of seismic, petrophysical, and outcrop data that are integrated with seismic modeling techniques. Other terrains with severe imaging problems, such as those associated with salt deposits, have received extensive atten- tion within the seismic processing industry. It is important to note that fundamentally different petrophysical prop- erties of volcanic and salt deposits suggest that new solu- tions should be considered to improve the subbasalt and intrabasalt images. We have primarily studied the large-volume volcanic province constructed in the northeast Atlantic during the Paleocene/Eocene continental breakup between Greenland and Europe. The crust on the Norwegian margin has been strongly affected by the volcanism, in particular in the outer part of the commercially exploitable Møre and Vøring Basins, where extrusive and intrusive rocks form an impor- tant part of the basin fill (Figure 1). Similar breakup com- plexes have been identified along large segments of the western Australian margin (Figure 2). The seismic images from both margins further suggest that magmatic mater- ial has been added to the base of the crust, leading to growth of the crust extended and thinned during the pre- ceding rifting phase. The volcanic breakup complexes on rifted margins record fundamental earth processes, and their construction may have had an important impact on earth history. The study of these features may address problems related to (1) mantle dynamics, including the presence and characteri- zation of mantle plumes; (2) the interplay of tectonism and magmatism in terms of the style of crustal deformation and crustal growth by addition of igneous rocks at various depths; (3) the temperature and rheology history of the crust, including sedimentary basins; (4) volcanic eruption and emplacement processes; and (5) the paleoenvironment through changes in basin geometry and ejection of parti- cles and gases into the atmosphere and hydrosphere. 342 THE LEADING EDGE MARCH 1999 MARCH 1999 THE LEADING EDGE 0000 Seismic characteristics of basaltic extrusive and intrusive rocks SVERRE PLANKE,EIVIND ALVESTAD, and OLAV ELDHOLM, University of Oslo, Norway Figure 1. Northeast Atlantic Volcanic Province and drill holes penetrating basaltic rocks. 553-990 = DSDP/ODP drill sites. FDD = Faeroe Island Deep Drilling; IRDP = Iceland Research Drilling Project; OS = Orkustofnun Deep Drilling; VSP = Eyjafardar VSP experiment; SDRS = Seaward Dipping Reflectors; MB = Møre Basin; VB = Vøring Basin. Bathymetry in km. Figure 2. Western Australia volcanic margin province. Black circles = DSDP/ODP drill sites. Yellow circles = wells penetrating breakup lavas. Bathymetry in km.