福島県いわき市沖の下部更新統磐城海底地すべり堆積体（Iwaki SLS）に認められるポップアップ構造の形態的・堆積学的な特徴と形成過程

Abstract

Morphometric and sedimentological characteristics, and formation process of Pop-up structures recognizedin the Lower Pleistocene Iwaki submarine landslide body (Iwaki SLS) in the Offshore Iwaki City, Fukushima Prefecture, Japan Hiroyuki AratoAbstract： The internal and external morphometric characteristics were described and formation process was discussed for the Iwaki submarine landslide (Iwaki SLS) , which was discovered at the sub-bottom of the continental shelf off Iwaki City, Fukushima Prefecture, Japan, by three-dimensional (3D) seismic interpretation.In this study area, the Lower Pleistocene was subdivided into nine layers based on the observation of seismic facies and seismic stratigraphic characteristics. Layers 1b to 4 were involved in the Iwaki submarine landslide, and twenty pop-up blocks and nine pop-up walls were formed in association with a group of conjugated reverse faults. The pop-up blocks, which were displaced upward with less deformation and remained almost as internal sedimentary structures, are interpreted to collapse at their fringe and eroded at the crest concurrently with pop-up displacement, supplying debris around the blocks.The pop-up walls are arranged in nine lines warped arcuately in the downstream direction. All arrays of pop-up walls terminate at the northeast end against a linear side escarpment, and are in direct contact with un-moved sediments of the same horizon in the northeast area. The side escarpment at the southwest side is interpreted as strike-slip echelon faults.The pop-up sequence was not revealed by the available dataset; however, circumstantial evidence suggests that sliding and pop-up movement in the Iwaki SLS occurred within a relatively short period of time.