https://www.google.com/url?sa=i&url=https%3A%2F%2Fko.wikipedia.org%2Fwiki%2F%25ED%258C%258C%25EC%259D%25BC%3ASea_of_Japan_Pliocene_map.svg&psig=AOvVaw2N2PxQdlEzrAi1ORLP3N5-&ust=1590419397867000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCIjOgo7kzOkCFQAAAAAdAAA