Tsunami Evacuation Travel Time Map for Humboldt County, CA, 2010, for Bridges Intact and a Slow Walking Speed

The travel time map was generated using the Pedestrian Evacuation Analyst model from the USGS. The travel time analysis uses ESRI's Path Distance tool to find the shortest distance across a cost surface from any point in the hazard zone to a safe zone. This cost analysis considers the direction of movement and assigns a higher cost to steeper slopes, based on a table contained within the model. The analysis also adds in the energy costs of crossing different types of land cover, assuming that less energy is expended walking along a road than walking across a sandy beach. To produce the time map, the evacuation surface output from the model is grouped into 1-minute increments for easier visualization. The times in the attribute table represent the estimated time to travel on foot to the nearest safe zone at the speed designated in the map title. The bridge or nobridge name in the map title identifies whether bridges were represented in the modeling or whether they were removed prior to modeling to estimate the impact on travel times from earthquake-damaged bridges.

本出行时间地图采用美国地质调查局（USGS）的行人疏散分析模型（Pedestrian Evacuation Analyst model）生成。本次出行时间分析借助ESRI的路径距离（Path Distance）工具，计算灾害区内任意点位至安全区的成本曲面最短通行距离。此项成本分析考量运动方向，并依据模型内置表格为更陡峭的坡地赋予更高通行成本。分析同时纳入不同土地覆被类型穿越所需的能量成本，假设沿道路行进相较于穿越沙滩消耗更少体力。为生成该时间地图，模型输出的疏散表面被按1分钟间隔进行分组，以提升可视化效果。属性表中的时间数值代表以地图标题指定的步行速度，抵达最近安全区的预估耗时。地图标题中的“bridge”与“nobridge”字样，用于标识建模过程中是否纳入桥梁模型，或是在建模前移除桥梁以评估地震损毁桥梁对出行时间的影响。