GIS BASED RELATIVE TSUNAMI HAZARD MAPS, HUMBOLDT COUNTY, CALIFORNIA

Tsunami hazard maps are generated using a geographical information systems (GIS) approach to depict the relative tsunami hazard of coastal Humboldt County in northern California. In contrast to previous mapping efforts that utilize a single line to represent inundation, hazard is displayed gradationally. A 2.5D surface is constructed to represent this hazard. Elevation, normally used for 2.5D surfaces, is substituted with hazard units. Criteria boundaries are used to separate regions of increasing hazard. Criteria boundaries are defined based on numerical modeling, paleoseismic studies, historical flooding, FEMA Q3 flood maps, and impacts of recent tsunamis elsewhere. Zones are constructed to further adjust the criteria with respect to a physically determined variable hazard (e.g. proximity to open ocean). A triangular irregular network (TIN) is constructed using hazard criteria boundaries as contours. Fabricated points are necessary to construct a hazard surface and are placed where criteria boundaries diverge or where hazard is nonlinear between criteria boundaries. Hazard is displayed as a continuous gradational color scale ranging from red (high hazard) through orange (medium), yellow (low) to gray (no hazard). The maps are GIS based to facilitate ready adaptation by planners and emergency managers. The maps are intended for educational purposes, to improve awareness of tsunami hazards and to encourage emergency planning efforts of local and regional organizations by illustrating the range of possible tsunami events.