Abstract

A large submarine slope failure, the Baiyun Slide Complex, has been discovered in the northern South China Sea. We describe the slide complex morphology, the seismic character of its structural elements and the slide evolution based on high-quality seismic reflection and multi-beam bathymetry data. The Baiyun Slide Complex has three major slide scars that show differences in headwall and sidewall geometry, the nature of the basal shear surfaces and the internal architecture of the deposits. From these observations, we propose a four-phase emplacement model. An extrapolation of the post-slide drape thickness (60 m) gives a rough age estimate for the mass transport events of 0.3 Ma. Pore pressure models for the unfailed continental slope in the vicinity of the Baiyun Slide are based on porosity measurements at nearby Ocean Drilling Program Site 1146. They show that excess pore pressure in slope sediments is anomalously high at a depth around 93 m, most probably as a consequence of a dramatic increase in sedimentation rates over the past 1.8 Ma. This excess pore pressure is proposed to be the major preconditioning factor for the slide initiation, possibly aided by volcano-tectonic activity and gas hydrate dissociation. The unfailed slope is stable under static conditions. However, a near-field earthquake of Mw 5 would suffice to induce a slope instability at c. 93 m depth.

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