Streamer tomography velocity models for the Gulf of Corinth and Gulf of Itea, Greece

International audienceThe Gulf of Corinth (GOC), Greece is a rapidly extending, active continental rift with a record of large, damaging earthquakes. An extensive multichannel seismic (MCS) survey of the GOC conducted in 2001 provided, in addition to the processed MCS images, the opportunity to constrain velocity structure using refracted arrivals recorded along a 6-km-long streamer. We use first-arrival traveltimes to derive tomographic P-wave velocity models for several profiles collected in the central portion of the GOC. Eight of the profiles are closely spaced, north– south lines crossing the GOC and extending into the Gulf of Itea (GOI); a ninth profile is an east–west-oriented tie line. The N–S profiles image the relatively simple velocity structure of the deep Corinth rift basin and more complicated structure of the northern margin of the currently active rift. Integration of the velocity models with migrated MCS sections shows that south of the GOI the basement, which comprises Mesozoic nappes, occurs at a velocity of 4.5 km s −1 in the velocity models, although the actual velocity at, or just below, the top of basement is probably closer to 5–5.5 km s −1. The maximum sediment thickness in the Corinth basin is 2.2 km. The basement shallows to the north into a fault-bounded terrace in the central region between the two gulfs. Sediment cover in this central region decreases in thickness from west to east. Beneath the GOI, low average velocities beneath the rift-onset reflector indicate the presence of pre-rift sediments. The pre-rift velocity structure in the GOI is complex, with significant lateral variation from west to east. The E–W line shows that high-velocity basement is shallow (≤1 km depth) and flat to the west of the GOI but dips ∼20 • east down to ∼1.5 km beneath the pre-rift sediments of the GOI