gas hydrate - CCOP

Mass Failure and Mass Flow Deposits in the Ulleung Basin and Korea
Plateau, East Sea, Korea : A Brief Review
Yi-Kyun Kwon 1) and Jang-Jun Bahk 1)
1) Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea
ABSTRACT: Many feature indicative of mass failure and mass flow deposits have
been observed in the Ulleung Basin and Korea Plateau, in the East Sea area of
Korea. In the early stages of back-arc opening of the East Sea, rapid subsidence
and related structural movements prompted slope instability and large-scale slope
failure resulting in mass flow deposits. In the transitional phase from back-arc
extension to compression, during the middle Miocene, active uplift and
compressional deformation also resulted in mass failure and the frequent input of
mass flows in the basin. From the late Miocene, in the back-arc closing stage, the
Ulleung Basin and Korea Plateau experienced rapid subsidence and episodic
tectonic deformation. In the late Miocene and Pliocene, the large-scale mass failure
and mass flow events were closely related with the tectonic deformation events.
After the latest tectonic event, in the middle Pliocene, the East Sea has remained
tectonically stable. However, during the Quaternary, although tectonically
quiescent, the Ulleung Basin and Korea Plateau were also affected by frequent
events of mass failure and mass flow. These events were probably related with sea
level fluctuations, climatic change, seismic shocks or expulsion of gas hydrate.
Keywords: mass failure, mass flow, Ulleung Basin, Korea Plateau, methane hydrate.
INTRODUCTION
The East Sea is a semi-closed marginal sea at the northwestern margin of the Pacific Ocean,
surrounded by the East Asian continent and the Japanese Islands. The sea is a back-arc basin
that consists of three deep sub-basins (Japan, Yamato, and Ulleung basins) separated by
topographic highs (Yamato Ridge, Korea Plateau, and Oki Bank) (Figure 1; e.g., Chough et
al., 2000). The physiography of the sea is characterized by a narrow shelf, steep slopes, and
deep depressions reaching more than 2,500 meters in water depth (e.g., Chough et al., 2000).
These physiographic characteristics have resulted in the frequent occurrence of slope failure
and mass flow (e.g., Chough et al., 2000)
During the past two decades, there have been a number studies concerning the genetic origin
of the slope failure and the resulting processes of mass flow (Chough and Lee, 1992; Lee et
al., 1996; Lee and Suk, 1998; Lee et al., 1999; Lee et al., 2002). This study aims to
summarize results of such research, to suggest a stratigraphic scheme for the Ulleung Basin
and Korea Plateau, and to describe the slope failure and mass flow events within this
stratigraphic framework.
New Energy Resources in the CCOP Region - Gas Hydrates and Coalbed Methane 105