3D joint refraction-reflection travel-time tomography of the Galicia 3D wide-angle dataset

The Galicia 3D reflection-refraction seismic experiment was carried out in 2013 at the Galicia rifted margin in the northeast Atlantic Ocean, west of Spain. The main geological features within the 64 by 20 km (1280 km2} 3D box investigated by the survey are the peridotite ridge (PR) composed of serpentinized peridotite, a series of fault bounded, rotated basement blocks and the S reflector, which has been interpreted to be a low angle detachment fault. Forty-four short period four component ocean bottom seismometers (OBS) and 28 ocean bottom hydrophones (OBH) were deployed within the 3D box. 3D multichannel seismic (MCS) profiles sampling the whole box were acquired with two airgun arrays of 3300 cu.in. fired alternately (in flip-flop configuration) every 37.5 m.

We present the results from 3D joint refraction-reflection traveltime tomography that constrains the P-wave velocity structure of the sediments, crust and uppermost mantle and the topography of the S reflector in the 3D box. Results are validated by synthetic tests, by comparisons with the results of previous first-arrival traveltime tomography and with images from the processed Galicia 3D MCS volume. The 3D P-wave velocity structure of the uppermost mantle yields the degree of serpentinisation and permits us to estimate the amount of water reaching the mantle through the higher permeability fault network. The crustal thickness retrieved by the present study allows us to estimate the degree of lithospheric extension, and to test the hypothesis of depth dependent stretching and the polyphase faulting, by comparing the wide-angle retrieved thinning with the one estimated from the fault heaves in the upper-crust.