Fig. 1

Wave equation datuming, modified from Berryhill (1984). The inverted triangles in the observation plane stand for hydrophones, and the hydrophones’ location after DC is indicated by dots"

Fig. 2

Schematic diagrams of MCS data acquisition before (a) and after (b) DC. Red stars represent the air-gun sources, inverted triangles in observation plane present hydrophones, and the hydrophones’ locations after DC are indicated by dots. Marine streamer is shown by the yellow line; green, red and blue rays indicate the convergence of the first and last channels and the final convergence, respectively"

Fig. 4

(a) Layered Penrose model of young oceanic formed along a fast-spreading ridge, modified from Vithana et al (2019); schematic ray paths of (b) original common shot gather data, (c) first-step DC of common shot gather data, and (d) second-step DC of common receiver gather data. Red star indicates the shot location, and green lines indicate the available picking range of first-arrival. Effective refractive wave, reflective wave and the unreliable first arrivals after DC are marked by white, red and black ray paths, respectively. The black rays correspond to the far offset seismic phases that cannot be recorded at the sea level"

Fig. 5

Comparison of seismic shot gather and traces from DC and synthetic seismograms. (a) Original common shot gather; (b) DC result of common shot gather; (c) synthetic seismogram of DC common shot gather; (d) DC result of common receiver gather; (e) synthetic seismogram of DC common receive gather; and (f) comparison of selected traces from DC result and synthetic seismogram. Seismic phases of layer 2A and 2B in (a~e) are indicated by red and green dash lines, respectively. Vertical white dashed lines indicate the locations of selected traces, and the enlarged real and synthetic traces are marked by green and red dashed lines in (f), respectively"

Fig. 6

Travel-time curves of observed and uncertainty (red dots with error bars), initial model (blue line) and final model (green line) before (a) and after (b) DC"

Fig. 7

(a) Real velocity model for original synthetic shot gathers; (b) 2D tomography velocity model before DC; (c) 1D velocity comparison of real model, initial model and tomography model before and after DC; and (d) 2D tomography velocity model after DC. The dotted white lines in (a), (b) and (d) correspond to the one-dimensional velocity models of black, blue and red lines, in (c), respectively"