Environmentally Critical Areas

Liquefaction-Prone Areas

Liquefaction-prone areas are areas typically underlain by cohesionless soils of low density, usually in association with a shallow groundwater table, that lose substantial strength during earthquakes.  Liquefaction-prone areas are specifically defined in Seattle Municipal code section 25.09.020 A.  Additional soil engineering studies and mitigation measures may be required in these areas to ensure that structures are designed to accommodate liquefaction.

Related Codes

• Seattle Municipal Code 25.09 Regulations for Environmentally Critical Areas
  • 25.09.020 ECA Definitions
  • 25.09.100 Development standards for liquefaction-prone areas

Related CAMs

• CAM 327A, Environmentally Critical Areas Exemptions, Relief from Prohibition on Steep Slope Development, and Modifications to Submittal Requirements — Application Instructions and Submittal Requirements
• CAM 327B, Environmentally Critical Areas — Small Project Waivers Application Instructions and Submittal Requirements
• CAM 328, ECA Exceptions

Related Director's Rules

• DR 3-93, General Duties and Responsibilities of Geotechnical Engineers