The primary purpose of geologically hazardous area regulations is to avoid and minimize potential impacts to life and property from geologic hazards.
(Ord. 11-0329 § 3 (Exh. 1); Ord. 19-0488 § 2 (Exh. 1))
Geologically hazardous areas include areas susceptible to erosion, landsliding, earthquake, or other geological events. These areas are further defined in WAC 360-190-120. They pose a threat to health and safety of citizens when incompatible development is sited in hazard areas. Such incompatible development may not only place itself at risk, but also may increase the hazard to surrounding development and use. Areas susceptible to one or more of the following types of hazards shall be designated as geologically hazardous areas:
A. 
Erosion hazard;
B. 
Landslide hazard;
C. 
Seismic hazard; and
D. 
Other geological events including debris flows and differential settlement.
(Ord. 11-0329 § 3 (Exh. 1); Ord. 19-0488 § 2 (Exh. 1); Ord. 24-0624 § 5 (Exh. C))
A. 
Erosion Hazard Areas. Erosion hazard areas are those areas containing soils which, identified by the U.S. Department of Agriculture’s Natural Resources Conservation Service or identified by a special study, as having a “moderate to severe,” “severe,” or “very severe” erosion potential. Erosion hazard areas include areas likely to become unstable, such as steep slopes, areas with unconsolidated soils, and channel migration zones.
B. 
High Landslide Hazard Areas. High landslide hazard areas are areas at high risk of landslides based on a combination of geologic, topographic, and hydrologic factors. They include areas susceptible because of any combination of bedrock, soil, slope (gradient), slope aspect, structure, hydrology, or other factors. Examples of these may include, but are not limited to, the following:
1. 
Areas of historic failures, such as:
a. 
Those areas delineated by the U.S. Department of Agriculture’s Natural Resources Conservation Service as having a significant limitation for building site development; or
b. 
Areas designated as Quaternary slumps, earthflows, mudflows, or landslides on maps published by the U.S. Geological Survey or State Department of Natural Resources; or
c. 
Areas identified on King County’s 2017 map of unstable slopes and as amended;
2. 
Areas with all three of the following characteristics:
a. 
Slopes steeper than 15 percent; and
b. 
Hillsides intersecting geologic contacts with a relatively permeable sediment overlying relatively impermeable sediment; and
c. 
Springs or groundwater seepage;
3. 
Areas that have shown movement during the post-glacial period (from 16,000 years ago to the present) or that are underlain or covered by mass wastage debris of that time period, as shown on U.S. Geological Survey, Washington Department of Natural Resources, or King County maps;
4. 
Areas potentially unstable because of rapid stream incision, stream bank erosion, and undercutting by wave action; and
5. 
Areas located in a canyon or on an active alluvial fan, presently or potentially subject to inundation by debris flows or catastrophic flooding.
C. 
Moderate Landslide Hazard Areas. Moderate landslide hazard areas are areas at moderate risk of landslides based on a combination of geologic, topographic, and hydrologic factors. They include areas susceptible because of any combination of bedrock, soil, slope (gradient), slope aspect, structure, hydrology, or other factors. Examples of these may include, but are not limited to, the following:
1. 
Areas with a slope of 40 percent or steeper and with a vertical relief of 10 or more feet. A slope is delineated by establishing its toe and measured by averaging the inclination over at least 10 feet of vertical relief.
D. 
Seismic Hazard Areas. Seismic hazard areas are locations subject to severe risk of damage as a result of earthquake-induced ground shaking, slope failure, settlement, soil liquefaction, lateral spreading, tsunami, or surface faulting. One indicator of potential for future earthquake damage is a record of earthquake damage in the past. Ground shaking is the primary cause of earthquake damage in Washington. The strength of ground shaking is primarily affected by:
1. 
The magnitude of an earthquake;
2. 
The distance from the source of an earthquake;
3. 
The type or thickness of geologic materials at the surface; and
4. 
The type of subsurface geologic structure.
Settlement, soil liquefaction, and lateral spreading occur in areas underlain by cohesionless, loose, or soft saturated soils of low density, typically in association with shallow groundwater. Tsunami or seiche waves triggered by an earthquake or seismically induced landslides can inundate shoreline-adjacent land, such as along Lake Washington or the lower reaches of the Sammamish River.
In Kenmore, seismic hazard areas include liquefaction-prone areas and a potential strand of the Southern Whidbey Island Fault Zone known as the Kenmore Lineament as designated by the Washington Department of Natural Resources.
E. 
Other Hazard Areas. Geologically hazardous areas shall also include areas determined by the city manager to be susceptible to other geological events, including debris flows and differential settlement.
(Ord. 11-0329 § 3 (Exh. 1); Ord. 19-0488 § 2 (Exh. 1); Ord. 24-0624 § 5 (Exh. C))