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Topographic anaglyph images are viewed using red-cyan glasses, which enables us to identify topographic relief features easily. In general, anaglyphs produced from the digital elevation model (DEM) are an effective means of identifying the tectonic geomorphology of both inland and seafloor. Few studies of tectonic geomorphology along coastal areas have been conducted because detailed topographical maps that combine data from inland and seafloor measurements have been lacking. This study aims to re-examine the tectonic geomorphology of the late Quaternary and present information related to the crustal deformation of the marine terraces and the seafloor on and around Ishigaki Island. This island is located in the southern part of the Nanseishoto Islands in Southwest Japan. Boulders transported by the giant tsunami in 1771 have remained on the coral reefs and marine terraces of this island. However, the source fault of the tsunami is unidentified. In this study, we interpret the topographic anaglyph images produced from 5-m- and 10-m-mesh inland DEMs of Japan provided by the Geospatial Information Authority of Japan. In addition, we examine a 2-s-mesh DEM of the seafloor obtained from cloud point data of multi-beam echo-sounding devices provided by the Japan Agency for Marine-Earth Science and Technology as well as a 2.8-s-mesh DEM re-processed from digital bathymetric charts using 1-m- to 2-m-interval counters from the Japan Hydrographic Association. The marine terraces in the southern part of Ishigaki Island were divided into three levels using the topographic anaglyph images. The heights of the old shorelines of these marine terraces in the east are higher than those in the west, suggesting that crustal movement tilted westward during the late Pleistocene. On the seafloor, 17-km-long northeast-trending steep and straight slopes are identified off the southeast coast of the island. The active reverse fault probably causes these scarps because small slopes were observed on the southeast dipping young slope distributed to the northeast extension of the steep slopes. Moreover, the active fault that cut the Ryukyu groups of the Pleistocene sediment just beneath the steep slope was depicted in some areas of the published geological map. This fault is named the Shiraho-Oki fault in this study and may be the source of the tilting to the west on the island. The resolution and accuracy of the DEM for the territory of Japan vary considerably between the inland and the seafloor. Detailed digital elevation data of the seafloor acquired by multi-beam echo-sounding devices should be obtained and stored to understand the tectonic geomorphology along the coastal areas., 本研究は科学研究費補助金（課題番号：16K01221）を使用しました。

Topographic anaglyph images were viewed with red–cyan glasses, making it possible to recognize topographic relief features easily. Anaglyphs produced from digital elevation model (DEM) data are a very effective way of identifying tectonic geomorphology. This paper aims to re-examine tectonic geomorphology and to present new tectonic maps for the late Quaternary in and around the Kanto Plain and Nansei Islands. This is achieved by interpretation of an extensive area of topographic anaglyph images produced from 5-m- and 10-m-mesh inland DEMs of Japan provided by the Geospatial Information Authority of Japan, and 2-s- and 14-s-mesh DEMs of the seafloor. The 2-s-mesh DEM of the seafloor is processed from cloud point data of multi-beam echo-sounding devices provided by the Japan Agency for Marine-Earth Science and Technology and re-processed from digital bathymetric charts, with 1- to 2-m-interval counters of the Japan Hydrographic Association. The extensive area of topographic anaglyphs produced from combined detailed DEM are shown to be useful for identifying tectonic geomorphology in plain areas, as well as of the seafloor, when the “naked” topography is exaggerated vertically. We identified for the first time an active anticlinal broad deformation of the Yamanote tableland surfaces where the capital of Japan is located, as well as fault geomorphology associated with the left lateral strike–slip fault along the Ayasegawa fault in the Kanto Plain, which was believed to be a reverse fault. We also found that the marine terraces are tilted to the south at Okinoerabujima Island and eastward at Tokunoshima Island, in the middle of the Nansei Islands. These tilts are related to the reverse faults along the steep slopes of the islands’ shelves that are divided into the Okinawa trough to the west. These reverse faults, which were believed to be a normal fault from the geological research, are newly identified on the basis of the interpretation of the tectonic geomorphology on anaglyph images produced from detailed DEM of the seafloor., 本研究は2013～2015年度研究費補助金基盤研究（C）（課題番号25350428，研究代表者：後藤秀昭），2006～2008年度研究費補助金若手研究（B）課題番号18700681，研究代表者：後藤秀昭），2005～2007年度研究費補助金基盤研究（A）（課題番号17200053，研究代表者：中田高），2011～2014年度研究費補助金基盤研究（A）（課題番号23240121，研究代表者：中田高）の一部を使用した。

資料番号: PA1210087000

本研究では，鶴見川流域を対象とした解析で再現性が確認されている分布型流出モデルを，海老川流域に適用することにより検証を行った．また，流域分割に関して，これまでの河道網・尾根線を描画した結果を目安に目視により決定する方法を改善し，数値標高モデル(DEM)を指標とした客観的な分割法を採用した．その結果，ハイドログラフはよい再現性を示し，本モデルの海老川流域への適用性が確認された．, In this study, a distributed runoff model, which has been verified by the flood runoff analysis in the Tsurumi River basin, is applied to the Ebi River basin. In addition, as for the division of study basin into small sub-basins, a new method based on the Digital Elevation Model (DEM) is adopted, instead of the former one which uses the generated river channel networks and ridge lines on the map as criteria for the manual work. As a result, the validity of the proposed model and its applicability to the urbanized basin are assessed by comparing the calculated hydrographs with the observed data.

地形学、水文学などの地球科学分野では、近年地理情報システム（GIS）を用いた解析が行われるようになってきた。GISで扱うデータにはベクトル型データとラスタ型データがあり、ラスタ型データには衛星画像や数値地形モデルなどがある。地形学、水文学の分野ではDEMから流路網を抽出し、これを用いて地形計測を行ったり流出モデルを構築するといったことが必要になる。流路網と絡めた場合、DEMはラスタ型データにも関らず、ネットワークの構造を持つことになる。このため、画像解析によく使われるフィルタ型の演算だけでは処理をすることができなくなる。そこで、本稿では流路ネットワークとDEMを使った地形解析の実際について述べ、そのアルゴリズムを紹介する。, Recent progress in computers and development of widespread spatial information enables us to use Geographical Information Systems (GIS) in earth sciences, such as geomorphology and hydrology. In general, GIS treat two kinds of data, raster type and vector type. Raster type data possess grid characteristics, and vector type data possess network ones. Satellite images and digital elevation models (DEM) are typical raster type data, and used as the basic dataset for geomorphology and hydrology. For geomorphology and hydrology, extraction of stream networks is one of important procedure to measure topographic characteristics and to construct runoff models. However, manual extraction of stream networks from topographic maps is very time consuming work. So automatic extraction of stream networks from DEM attracts attention of many researchers. Stream networks simulated from DEM are called as drainage direction matrices (DDM). DDM possess combination characteristics of grid characteristics of raster type and network one of vector type. Therefore, it is impossible to handle DDM with simple use of filter operators, which majorly used in image processing software and GIS. So we should consider both characteristics of vector and raster type data when we treat DEM and DDM. In this paper, we explain the basic algorithms to handle DEM and DDM in geomorphology and hydrology.