## 4 Results  
### Seismic Sequence Analysis  
Based on seismic sequence interpretation, seven seismic sequence boundaries, including the seafloor, were identified in the channel-developed interval, which from bottom to top are named as SB1 to SB7, respectively corresponding to N40, N45, N50, N60, N70, N80, and seabed (Figures 2-4) [15; 21; 35; 37]. These sequence boundaries subdivide the interval into six seismic sequences, called sequences S1-S6 from bottom to top (Figures 2 and 3). According to previous regional stratigraphic classification [35], the sequence boundary N40 (base of sequence S1) is linked to the Kaikoura Oroogeny, which occurred at approximately 11-10 Ma, making the base of the Late Miocene. The sequence boundary N60 (base of sequence S4) resulted from enhanced uplift and erosion in the Southern Alps at \(\sim\)5 Ma [9; 11; 14], thus marking the base of the Pliocene. The sequence boundary N80 (base of sequence S6) corresponds to the onset of Quaternary global glacial/interglacial climatic cycles and the development of an icecap along the alpine region of South Island (about 2.5 Ma) [9; 10], thus marking the base of the Quaternary. Therefore, sequences S1-S3 are tentatively identified as the Upper Miocene, sequences S4-S5 as the Pliocene, and sequence S6 as the Quaternary. Sequence S2 is composed of reflections of low-to-moderate amplitude and moderate-to-high continuity, with local areas containing concave-upward reflections that exhibit a complex fill configuration (Figures 3 and 4). Similar to sequence S1, this sequence displays a larger thickness in the east than in the west (Figure 6B). However, the depositional center shifts westward, with the largest thickness ranging from 160 to 250 ms TWT in the central portion of the study area (Figure 6B). A small depositional center with a thickness of 60 to 120 ms TWT is located in the north of the study area, with thickness gradually thinning southwestward (Figure 6B). Sequence S3 consists of low-to-moderate amplitude, high-continuity, and low-frequency reflections, normally showing divergent fill structures (Figures 3 and 4). In comparison to sequences S1 and S2, the sedimentary center of this sequence further shifted westward (Figure 6C). Three belted depositional centers are located in the center of the study area, with thicknesses ranging from 60 to 160 ms TWT. There is another small depositional center in the north of the study area (Figure 6C), which is 40-90 ms TWT in thickness. Its strata are characterized by low-to-moderate amplitude and high-continuity reflections of a wedge-shaped divergent configuration. Figure 3: (**A**) Uninterpreted and (**B**) interpreted dip-oriented (NW-SE) seismic profiles showing the rift geometry and seismic sequence subdivision in the study area. See Figure 1B for profile location. Sequence S4 is primarily characterized by low-to-moderate amplitude and high-continuity reflections (Figures 3 and 4). Different from sequences S1-S3, the main depositional center of this sequence is distributed in the west of the study area (Figure 6D). The strata exhibit moderate-to-high amplitude and high-continuity reflections of a wedge-shaped divergent configuration, with a thickness ranging from 60 to 110 ms TWT (Figures 4B and 6D). The  
Figure 4: (**A,C**) Uninterpreted and (**B,D**) interpreted dip-oriented (NW-SE) seismic profiles showing the characteristics of the tributary channels (C1 and C2) and related depositional elements. See Figure 1B for profile locations. eastern and southern areas show a relatively small thickness ranging from 0 to 40 ms TWT (Figure 6D) and exhibit wedge-shaped divergent and subparallel reflections. Similar to sequence S4, sequence S5 consists of low-to-moderate amplitude and high-continuity reflections (Figures 3 and 4). The seismic reflection amplitude of the strata in the east is significantly weaker than that in the west (Figure 6E). The depositional centers of this sequence are located in the west and south of the study area, with thicknesses ranging from 50 to 140 ms TWT (Figure 6E).