A. Geologically hazardous areas include areas in the City that are designated by the City Planner as potentially not suited to development based on public health, safety or environmental standards, because of such areas’ susceptibility to erosion, sliding, earthquake, or other geological processes as designated by WAC 365-190-080(4).
B. The City Planner may designate areas as geologically hazardous, including erosion, landslide, and seismic hazard areas, consistent with the following:
1. Erosion hazard areas are areas identified by the U.S. Department of Agriculture’s Natural Resources Conservation Service as having a moderate-to-severe, severe, or very severe rill and inter-rill (sheet wash) erosion hazard.
2. Landslide hazard areas are areas subject to landslides based on geology, soils, topography, and hydrology, including:
a. Areas delineated by the U.S. Department of Agriculture’s Natural Resources Conservation Service as having a severe limitation for building site development;
b. Areas mapped by the Washington Department of Ecology (Coastal Zone Atlas) or the Washington State Department of Natural Resources (slope stability mapping) as unstable (U or class 3), unstable old slides (UOS or class 4), or unstable recent slides (URS or class 5);
c. Areas designated as quaternary slumps, earthflows, mudflows, lahars, or landslides on maps published by the U.S. Geological Survey or Washington State Department of Natural Resources;
d. Areas where the following coincide: slopes steeper than fifteen percent, relatively permeable sediment overlying a relatively impermeable sediment or bedrock, and ground water seepage;
e. Areas that have shown movement in the past ten thousand years or that are underlain or covered by mass wastage debris of that time frame;
f. Slopes that are parallel or sub-parallel to planes of weakness (such as bedding planes, joint systems, and fault planes) in subsurface materials;
g. Slopes steeper than eighty percent subject to rock fall during seismic shaking;
h. Areas potentially unstable because of rapid stream incision, stream bank erosion, and undercutting by wave action;
i. Areas at risk from snow avalanches;
j. Canyons or active alluvial fans subject to debris flows or catastrophic flooding; and
k. Slopes of forty percent or steeper with a vertical relief of ten or more feet except areas composed of consolidated rock.
3. Seismic hazard areas are areas subject to severe risk of damage as a result of earthquake induced ground shaking, slope failure, settlement, soil liquefaction, lateral spreading, or surface faulting. One indicator of potential earthquake damage is a record of past earthquake damage. Settlement and soil liquefaction occur in areas underlain by cohesionless, loose, or soft-saturated soils of low density, typically in association with a shallow ground water table.
4. Mine hazard, volcanic, and tsunami hazard areas (none known to be present in the City: see WAC 365-190-080).
5. Other geologically hazardous areas including areas susceptible to mass wasting, debris flows, rock falls, and differential settlement.