한반도의 동해 대륙주변부의 지각구조 : 심부 탄성파탐사결과

Abstract

Despite the various opening models of the southwestern part of the East Sea (Japan Sea) between the KoreanPeninsula and the Japan Arc, the continental margin of the Korean Peninsula remains unknown in crustal structure. Asa result, continental rifting and subsequent seafloor spreading processes to explain the opening of the East Sea have notbeen adequately addressed. We investigated crustal and sedimentary velocity structures across the Korean margin into theadjacent Ulleung Basin from multichannel seismic reflection and ocean bottom seismometer data. The Ulleung Basinshows crustal velocity structure typical of oceanic although its crustal thickness of about 10 km is greater than normal.The continental margin documents rapid transition from continental to oceanic crust, exhibiting a remarkable decrease incrustal thickness accompanied by shallowing of Moho over a distance of about 50 km. The crustal model of the marginis characterized by a high-velocity (up to 7.4 km/s) lower crustal (HVLC) layer that is thicker than 10 km under theslope base and pinches out seawards. The HVLC layer is interpreted as magmatic underplating emplaced duringcontinental rifting in response to high upper mantle temperature. The acoustic basement of the slope base shows anigneous stratigraphy developed by massive volcanic eruption. These features suggest that the evolution of the Koreanmargin can be explained by the processes occurring at volcanic rifted margins. Global earthquake tomography supportsour interpretation by defining the abnormally hot upper mantle across the Korean margin and in the Ulleung Basin.