3D GRAVITY MODELLING FOR ANYONGBOK SEAMOUNT IN THE EAST SEA

Abstract

A seamount chain with an approximately WNW trend is observed in the northeastern Ulleung Basin. It has been argued that these seamounts, including two islands called Ulleung and Dok islands, were formed by a hotspot process or by ridge related volcanism. Many geological and geophysical studies have been done for all the seamounts and islands in the chain except Anyongbok Seamount, which is close to the proposed spreading ridge. We first report morphological characteristics, sediment distribution patterns, and the crustal thickness of Anyongbok Seamount using multibeam bathymetry data, seismic reflection profiles, and 3D gravity modeling. The morphology of Anyongbok Seamount shows a cone shaped feature and is characterized by the development of many flank cones and flank rift zones. The estimated surface volume is about 60km3, and implies that the seamount is smaller than the other seamounts in the chain. No sediments have been observed on the seamount except the lower slope, which is covered by more than 1,000m of strata. The crustal structure obtained from a 3D gravity modeling (GFR=3.11, SD 3.82=mGal) suggests that the seamount was formed around the boundary of the Ulleung Plateau and the Ulleung Basin, and the estimated crustal thickness is about 20km, which is a little thicker than other nearby seamounts distributed along the northeastern boundary of the Ulleung Basin. This significant crustal thickness also implies that Anyongbok Seamount might not be related to ridge volcanism.