A Seismic Study of the Rift Zone in Northern Iceland

. The complex geological-geophysical expedition of the USSR Academy of Sciences jointly with the National Energy Au thority (Orkustofnun) of Iceland conducted in 1977 a detailed seismic investigation of the flood basalt and rift zones in northern Iceland, similar to studies in southwestern Iceland. Continuous seismic profiling with 4-6 shot points was carried out across a total length of 90 km. In the flood basalt zone shallow refracting horizons were observed with V p= 4.3- 4.5 km/s and tilted toward the rift zone. They closely correspond to dense sheets of flood basalts mapped geologically. Refracting and reflecting horizons at 2 to 12 or 15 km depth are tilted more gently in the same direction. A slight depression filled with neovolcanic formations with VP< 3 km/s exists near the surface in the rift zone. Reflectors with steep tilt can be traced to depths of 15 km. The deepest part of the depression is west of Myvatn in the region of current volcanism and rifting. A seismically homogeneous body without reflectors was detected under this region at I 0-15 km depth. On the whole, the structure of the rift zone in northern Iceland is similar to, but more complex than, that of southwestern Iceland.