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March 2004 |
JEGM for nationwide hazard assessment
Japan Engineering Geomorphologic Classification Map (JEGM) is a GIS-based map of ground conditions for all of Japan, consisting of approximate 380,000 grid cells of 1 x 1 km each
Information on local geologic and ground conditions plays important roles in the evaluation and forecasting of hazards, especially in real-time disaster-assessment systems. However, neither digital databases nor paper maps of ground conditions throughout Japan have yet been compiled in a unified form. Under the given circumstances, our research group have created the ‘JEGM’.
ATTRIBUTE DATA
The following ground-condition-related and landform-related hazards were purposed by the map: (1) amplification of seismic motion, (2) soil liquefaction, (3) earthquake-, rainfall- and volcanic-eruption-induced slope failure and landslide, (4) rainfall-, storm-surge-induced flood, and (5) tsunami inundation. The factors controlling these phenomena were reviewed with respect to various kinds of prediction models to identify the most appropriate attributes that might be included in the database. The review resulted in a list of the major factors on land characteristics, namely: (1) soil and rock type and its ages and properties, (2) ground-water condition, (3) land form or slope steepness, and (4) artificial changes to the land.
The geomorphologic classification was eventually employed as a major attribute of the map, as this classification system is known to analyze and classify the land into units based on physical characteristics of the land, i.e., aspects of: relief; geomorphic processes; rock characteristics; soil characteristics; and hydrologic characteristics [1]. In addition, the classification was previously found to correlate well with data on storm-surge-induced flood zones [2], tsunami inundation zones [2], susceptibility to soil liquefaction [2], [3], average shear wave velocity to 30 metres [4], and site amplification of earthquake ground motion [5]. Besides several attributes were assigned to each cell in the layers of the map: subsurface geology, slope angle, and relative relief (Fig. 1). They are important factors in the evaluation of landslide and slope-failure potential for hilly regions.
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