14.100.450 Geologically Hazardous Areas—General Requirements.
A. Alterations of geologically hazardous areas or associated buffers may only occur for activities that:
1. Will not increase the threat of the geological hazard to adjacent properties beyond predevelopment conditions;
2. Will not adversely impact other critical areas;
3. Are designed so that the hazard to the project is eliminated or mitigated to a level equal to or less than predevelopment conditions; and
4. Are determined to be safe as designed and under anticipated conditions by a qualified engineer or geologist, licensed in the state of Washington.
B. Critical facilities shall not be sited within geologically hazardous areas unless there is no other practical alternative.
C. In addition to the provisions of this chapter, alterations of geologically hazardous areas or associated buffers must conform to city construction standards and building codes.
D. Seismic Hazard Areas Standards. Development may be allowed in seismic hazard areas when all of the following apply:
1. If evaluation of site-specific subsurface conditions by a qualified professional demonstrates that the proposed development site is not subject to the conditions indicating seismic risk, the provisions of this subsection shall not apply.
2. If a site is subject to seismic risk, the applicant shall implement appropriate engineering design based on analysis by a qualified professional of the best available engineering and geological practices that either eliminates or minimizes the risk of structural damage or injury resulting from seismically induced settlement or soil liquefaction including compliance with the following criteria:
a. Subdivision within a seismic hazard area shall assure that each resulting lot has sufficient buildable area outside of the hazard area or that appropriate limitations on building and reference to appropriate standards are incorporated into subdivision approval and may be placed as restrictions on the face of the plat;
b. Structures in seismic hazard areas shall conform to applicable analysis and design criteria and provisions of building and construction codes as currently adopted by the city. The city may require the submission of a geotechnical analysis to determine that the proposal conforms with applicable building and construction codes.
c. Public roads, bridges, utilities and trails shall be allowed when there are no feasible alternative locations and geotechnical analysis and design are provided that ensure the roadway, bridge and utility structures and facilities will not be susceptible to damage from seismic induced ground deformation. Mitigation measures shall be designed in accordance with the most recent version of the American Association of State Highway and Transportation Officials (AASHTO) Manual or other appropriate document(s) adopted for use by the city.
d. Critical facilities shall not be located in seismic hazard areas unless mitigation shall be provided which renders the proposed development as stable as if it were not located within a seismic hazard area. The director may waive or reduce engineering study and design requirements for alterations in seismic hazard areas for:
(1) Mobile homes;
(2) Additions or alterations to existing structures that do not increase occupancy or significantly affect the risk of structural damage or injury; and
(3) Buildings that are not dwelling units or used as places of employment or public assembly.
E. Tsunami Hazard Areas Standards. Activities on sites containing areas susceptible to inundation due to tsunami hazards shall require an evacuation and emergency management plan. The city may use the performance standards for frequently flooded areas (see Chapter 15.55) as guidance in reviewing new structures proposed in tsunami hazard areas.