Three dimensional high-resolution imaging of the Deep Galicia Margin using wide-angle seismic data

Abstract:

The Galicia margin, west of Iberia, is one of the most studied magma-poor rifted margins to understand the rifting process leading to continental breakup. Seismic imaging has been instrumental in understanding rifting in the Galicia margin. We have derived a high-resolution P-wave velocity model of the Deep Galicia margin (DGM) where the final breakup of the continental crust occurred. The velocity model was derived employing a 3D acoustic full waveform inversion (FWI) technique in the time domain using sparsely acquired wide-angle ocean bottom seismometer data. The model was validated by tracking phase changes of the first arrivals during the inversion, and by comparing the predicted waveforms with the observed for all the instruments. In addition, the anomalies introduced by FWI were validated by performing synthetic inversion runs by recovering the anomalies using a synthetic dataset predicted using the final velocity model as observed dataset.

Using the high-resolution 3D model, we attempted to understand the nature of the crystalline crust by comparing the velocity range of the crystalline crust in the DGM with other similar tectonic settings. The velocity limits in the DGM include velocities of both the upper and lower crust observed in other similar settings, indicating that it is comprised of both upper and lower crust. Unlike in many other settings, there is no clear evidence in the P-wave velocity profiles for a separate upper and lower crust within the crystalline crust. The high-resolution model also shows an evidence for exhumation of the lower crust under the footwall of the fault blocks to accommodate the extension. We generated a serpentinization map of the DGM at a depth of 100 ms below the S-reflector, which shows that the topography highs correlate with the local highs on the serpentinization map suggesting effects of buoyancy.