The crusta! structure of the Mesozoic deep Galicia margin and adjacent ocean continent boundary (OCB) was investigated by seismic reflection (includmg pre-stack depth migration and attenuation of seismic waves with time). The seismic data were calibrated using numerous geological samples recovered by drilling and/or by divmg with submersible. The N S trending margin and OCB are divided in two distinct segments by NE-SW synrift transverse faults locally reactivated and inverted by Cenozoic tectonics. The transverse faulting and OCB segmentation result from crusta! stretching probably in a NE-SW direcuon dunng the rifling stage of the margin in early Cretaceous t1mes. The Cenozoic tectonics arc related to Iberia-Eurasia convergence in Palaeogcne times (Pyrenean event). In both segments of the deep margin, the seismic crust is made of four horizontal layers: (I) two sedimentary layers corresponding to post-and syn-rift sequences, where velocity ranges from 1.9 to 3.5 km s 1 , and where the Q factor is low, the two sedimentary layers being
We present an automatic algorithm to implement nonhyperbolic velocity analysis in VTI media. The approach is based on the use of nonhyperbolic traveltime equations that are accurate at large offsets and in anisotropic media. This is combined with an efficient parameterization to allow appropriate search for the moveout parameters (zero-offset traveltime, moveout velocity, and effective anellipticity). The raw coherency curve obtained at each CMP gather is used to filter out noisy picks and detects automatically the reflected energy with the respective parameters which makes the procedure automatic avoiding thus the tedious task of interpreting velocity spectra and picking the moveout parameters. Dix-type inversion formulae are used to retrieve interval parameters from the picked values to be used for later processing.
To: "Automatic nonhyperbolic velocity analysis, " Brahim Abbad, Bjørn Ursin, and Didier Rappin, Geophysics, 74, no. 2, U1-U12.There was a misprint in equation (11) in the paper, a multiplication by 4 is required in the denominator of the fi rst term instead of 2 and another division by the number of traces N is needed for the second term (semblance coeffi cient).The correct equation becomes then (11) This makes the bootstrapped differential semblance (BDS) coeffi cient ranges between 0 and 1. We apologize for the error and wish to thank Andrew J. Carter, Statoil, for making us aware of this mistake.
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