True Volumes of Slope Failure Estimated From a Quaternary Mass‐Transport Deposit in the Northern South China Sea

Abstract

Submarine slope failure can mobilize large amounts of seafloor sediment, as shown in varied offshore locations around the world. Submarine landslide volumes are usually estimated by mapping their tops and bases on seismic data. However, two essential components of the total volume of failed sediments are overlooked in most estimates: (a) the volume of subseismic turbidites generated during slope failure and (b) the volume of shear compaction occurring during the emplacement of failed sediment. In this study, the true volume of a large submarine landslide in the northern South China Sea is estimated using seismic, multibeam bathymetry and Ocean Drilling Program/Integrated Ocean Drilling Program well data. The submarine landslide was evacuated on the continental slope and deposited in an ocean basin connected to the slope through a narrow moat. This particular character of the sea floor provides an opportunity to estimate the amount of strata remobilized by slope instability. The imaged volume of the studied landslide is ~1035 ± 64 km3, ~406 ± 28 km3 on the slope and ~629 ± 36 km3 in the ocean basin. The volume of subseismic turbidites is ~86 km3 (median value), and the volume of shear compaction is ~100 km3, which are ~8.6% and ~9.7% of the landslide volume imaged on seismic data, respectively. This study highlights that the original volume of the failed sediments is significantly larger than that estimated using seismic and bathymetric data. Volume loss related to the generation of landslide‐related turbidites and shear compaction must be considered when estimating the total volume of failed strata in the submarine realm.

Tsunamigenic Potential of the Baiyun Slide Complex in the South China Sea

“…The spatial coverage of Slide 5 corresponds to the evacuation zone of MTDb identified by Sun, Cartwright, et al () with a total area of ~5,500 km 2 and estimated volume of 863 km 3 (combined volume of MTDb and MTDo2). Informed by Sun, Alves, et al (), we design Slide 6 with an even larger spatial coverage (~9,626 km 2 ) and an increased slide volume (~1,024 km 3 ) than Slide 5. Although Slide 6 could represent the worst‐case scenario among the six synthetic cases, we deem Slide 5 as the most credible scenario since its spatial coverage of both evacuation and deposit zones and volumes are evidenced in the 2‐D/3‐D seismic data (Sun, Cartwright, et al, ).…”

“…Although Slide 6 could represent the worst‐case scenario among the six synthetic cases, we deem Slide 5 as the most credible scenario since its spatial coverage of both evacuation and deposit zones and volumes are evidenced in the 2‐D/3‐D seismic data (Sun, Cartwright, et al, ). The spatial thickness distributions of all the landslides (Table ) are extracted/specified according to the thickness distribution (elevation difference between the present‐day and the restored prefailure sea bed) restored by Sun, Alves, et al (). These six scenarios provide diverse scenarios that allow us to investigate how the initial water depth of the landslide, sliding direction, and slide volume affect the resulting tsunami hazard.…”

“…(e) Slide 5 corresponds to the evacuation zone of MTDb identified by Sun, Cartwright, et al (). (f) Slide 6 is inferred from Sun, Alves, et al ().…”

“…The tsunami hazard research in the South China Sea (SCS) has been mostly focused on megathrust earthquakes along the Manila Trench, which is believed to be the primary tsunami source capable of generating basin‐wide tsunami (e.g., L. Li, Switzer, et al, ; L. Li et al, ; Liu et al, ; Megawati et al, ; Sepúlveda et al, ; Terry et al, ). However, recent activity in submarine exploration has produced high‐resolution bathymetric and 2‐D/3‐D seismic data that reveal hundreds of submarine landslides in the continental slopes of the SCS including those observed in the Pearl River Mouth Basin (Chen et al, ; He et al, ; W. Li, Wu, Völker, et al, ; Sun, Alves, et al, ; Sun, Cartwright, et al, ; Sun et al, ; Sun et al, ; Wang et al, ; Wu et al, ), offshore southwest Taiwan (Su et al, ), southeast Hainan (e.g. W. Li, Alves, et al, ; Wang et al, ), north Borneo (Gee et al, ), and west Luzon (Armada, ).…”

“…However, recent activity in submarine exploration has produced high-resolution bathymetric and 2-D/3-D seismic data that reveal hundreds of submarine landslides in the continental slopes of the SCS including those observed in the Pearl River Mouth Basin He et al, 2014;W. Li, Wu, Völker, et al, 2014;Sun, Alves, et al, 2018;Sun, Cartwright, et al, 2018;Sun et al, 2017;Sun et al, 2008;Wang et al, 2014;Wu et al, 2011), offshore southwest Taiwan (Su et al, 2012), southeast Hainan (e.g. W. Li, Alves, et al, 2015;Wang et al, 2013), north Borneo (Gee et al, 2007), and west Luzon (Armada, 2016).…”