Earthquake Preparedness & Seismic Risk in Seattle#

Washington has the second-highest earthquake risk in the United States, after California, with more than 1,000 earthquakes occurring in the state each year. (DNR | MRSC) Seattle sits near three distinct seismic sources capable of producing damaging earthquakes, and approximately 15% of the city’s land area is built on soil prone to ground failure during shaking. (Seattle OEM) This guide covers the seismic hazards, the city’s vulnerable building stock, preparedness programs, and what urbanists and advocates should know.

Seismic hazard sources#

Seattle’s earthquake risk comes from three distinct geologic sources, each producing different types of earthquakes at different frequencies and intensities.

Cascadia Subduction Zone#

The Cascadia Subduction Zone (CSZ) is an approximately 1,100-kilometer fault running offshore from northern California to Vancouver Island, where the Juan de Fuca plate dives beneath the North American plate. It is capable of producing magnitude 9.0+ megathrust earthquakes. The last full-rupture event occurred on January 26, 1700, generating a tsunami recorded in Japan. USGS estimates a 10-15% probability of a magnitude 9 CSZ earthquake in the next 50 years. (USGS Earthquake Probabilities | DNR Earthquakes and Faults)

Seattle Fault Zone#

The Seattle Fault Zone is an east-west trending zone of shallow thrust faults running directly beneath the city, from Bainbridge Island through the area near I-90. It is capable of producing magnitude 7.0-7.5 earthquakes at shallow depths (less than 25 km). The most recent large event occurred around 900-930 CE, causing significant land-level changes and a tsunami on Elliott Bay. (WA State Geology News) A 2026 USGS study found that secondary faults within the zone rupture approximately every 350 years over the past 2,500 years, more frequently than the main fault. (USGS) USGS estimates a 17% probability of a magnitude 6.5+ crustal fault earthquake in the Puget Sound region in the next 50 years. (USGS Earthquake Probabilities)

Deep intraplate earthquakes#

Deep earthquakes occur within the subducting Juan de Fuca plate at depths of 40-70 km. These were responsible for Seattle’s three most damaging modern earthquakes (1949, 1965, and 2001). Deep earthquakes of magnitude 6.0+ occur on average every 30 years in the Puget Sound region, with an estimated 84-85% probability of one in the next 50 years. (USGS Pacific Northwest Hazards)

Historical earthquakes#

1949 Olympia earthquake (magnitude 6.7-7.1)#

On April 13, 1949, a deep intraplate earthquake struck with its epicenter near Joint Base Lewis-McChord. Eight people were killed and property damage reached an estimated $25 million (approximately $265 million in today’s dollars). Nearly every building in Pioneer Square was damaged, with effects ranging from lost parapets to entire floors requiring demolition. (DNR Earthquakes and Faults)

1965 Puget Sound earthquake (magnitude 6.7)#

On April 29, 1965, another deep intraplate earthquake struck the same region at 59 km depth. Three people were killed by falling debris. The largest structural damage occurred at Boeing plants in Renton and southwestern Seattle, areas built on fill and mud flats. This earthquake prompted installation of the Pacific Northwest Seismic Network in 1969. (DNR Earthquakes and Faults)

2001 Nisqually earthquake (magnitude 6.8)#

On February 28, 2001, a deep intraplate earthquake struck beneath Anderson Island at 52 km depth. No one was killed directly, though approximately 400 people were injured. Total damage reached an estimated $2 billion. (PNSN)

Key damage included:

• Unreinforced masonry buildings in Pioneer Square sustained the worst structural damage, with brick shedding from parapets and diagonal cracking in walls (PNSN)
• The Alaskan Way Viaduct sank several inches, catalyzing the $3.35 billion SR 99 tunnel replacement project (WSDOT)
• Sand boils and liquefaction occurred in SODO and Harbor Island, on tidal flats that had been filled and built upon (UW News)
• The Sea-Tac Airport air traffic control tower sustained shattered windows and internal damage, forcing controllers to a temporary structure within 36 minutes (Port of Seattle)

Liquefaction zones#

Liquefaction occurs when water-saturated, loosely packed soil loses its strength during earthquake shaking and behaves like a liquid. About 15% of Seattle’s total area consists of soil prone to ground failure in earthquakes. (Seattle OEM)

Most vulnerable areas#

Seattle’s highest-risk liquefaction zones sit on artificial fill placed over estuarine mud during the city’s early 20th-century regrades, when hillsides were sluiced and fill was dumped into Elliott Bay and the Duwamish estuary. (Seattle SHIVA Earthquake Assessment (PDF)) The most vulnerable neighborhoods include:

• Duwamish Valley (SODO, Georgetown, Harbor Island) – experienced pervasive liquefaction during the 2001 Nisqually earthquake, on tidal flats that had been filled and built upon (UW News)
• Pioneer Square – built on filled tideflats; sustained the worst building damage in 2001
• Interbay – low-lying area between Queen Anne and Magnolia, built partly on fill
• Rainier Valley – portions built on soft alluvial soils
• Shoreline areas – waterfront zones across the city

Infrastructure at risk#

Both major north-south corridors (I-5 and SR 99/SR 509) pass through liquefaction zones. King County International Airport (Boeing Field) sits entirely within the liquefaction zone, as do most of the city’s rail and marine terminals. (Seattle SHIVA Earthquake Assessment (PDF))

SDCI updated Seattle’s Environmentally Critical Areas liquefaction-prone area map in 2023, replacing a map based on 1962 data with one using a 2005 geologic map and updated earthquake ground motions. (SDCI Building Connections)

Unreinforced masonry buildings#

Unreinforced masonry (URM) buildings – typically brick structures built before 1945 that lack steel reinforcement and structural connections – are the most dangerous building type in earthquakes. Seattle has approximately 1,100 URM buildings, and over 22,000 people live or work in them. Pioneer Square and the Chinatown-International District together contain approximately 15% of all the city’s URMs. (Seattle SDCI)

SDCI estimates Seattle has an 86% chance of experiencing a damaging earthquake within 50 years. (Seattle SDCI)

Retrofit program timeline#

Seattle’s path toward mandatory URM retrofits has been gradual:

• 2001: The Nisqually earthquake causes over $8 million in URM damage, renewing urgency (Seattle SDCI URM Timeline)
• 2017: URM Policy Committee recommends the “Bolts Plus” retrofit standard (The Urbanist)
• 2021: City Council passes Resolution 32033, directing SDCI to pursue a mandatory retrofit ordinance (Seattle SDCI URM Timeline)
• November 2024: Voluntary URM retrofit code adopted as part of the 2021 Seattle Existing Building Code, introducing an Alternate Method for Retrofit that reduces estimated costs by up to 70% (SDCI Building Connections)
• February 2025: The Poll Building at 110 Union Street becomes the first building to receive official “Retrofitted” URM status (SDCI Building Connections)
• December 2025: 76 URM buildings officially recognized as retrofitted (approximately 7% of all URMs) (SDCI Building Connections)
• January 2026: SDCI implements a 50% reduction in permit and plan review fees for seismic retrofit projects (SDCI Building Connections)
• Future: Mandatory retrofit ordinance planned, with compliance timelines of 7 years (critical risk), 10 years (high vulnerability), and 13 years (medium vulnerability) after adoption (Seattle SDCI FAQ)

What a retrofit involves#

A URM seismic retrofit typically involves anchoring exterior walls to the roof and floor structures to prevent walls from falling outward during shaking. The “Bolts Plus” standard recommended for Seattle is a life-safety measure – it does not guarantee a building will remain usable after a major earthquake, but it substantially reduces the risk of collapse and death. (Seattle SDCI FAQ)

Retrofit costs and funding#

Retrofit costs in Seattle can exceed $100 per square foot. The Alternate Method adopted in 2024 reduced estimated costs by up to 70%. The National Institute of Building Sciences estimates that every $1 invested in seismic retrofitting saves $13 in future losses. (SDCI Building Connections)

Current and proposed funding mechanisms include:

• FEMA grants – SDCI received a 2023 FEMA grant for retrofit cost-benefit analyses in the Chinatown-ID and Pioneer Square (SDCI Project Documents)
• C-PACER financing – authorized by state HB 2405 (signed 2020), allows property owners to finance seismic upgrades through their property tax bill (Shift Zero | WA Legislature)
• Transfer of Development Rights (TDR) – proposed program to generate retrofit credits by selling unused development capacity from URM properties (ASAP!)
• Fee reductions – 50% permit and plan review fee reductions effective January 2026 (SDCI Building Connections)

Comparison with other cities#

Sources: Seattle SDCI | Portland Permitting & Development | LA Division 88 (UpCodes)

Studies of California cities found voluntary retrofit programs achieved only 19% compliance, while mandatory programs achieved substantially higher rates. (Seattle SDCI FAQ)

Major seismic infrastructure investments#

The Nisqually earthquake catalyzed two of Seattle’s largest infrastructure projects:

• Alaskan Way Viaduct replacement: The $3.35 billion SR 99 tunnel, opened February 2019, replaced the seismically vulnerable double-deck viaduct. The tunnel meets standards for a 2,500-year earthquake. (WSDOT)
• Seawall rebuild: A roughly $350 million project to replace the deteriorating 1934 Alaskan Way Seawall, anchored by a $290 million voter-approved bond in 2012 with additional funding from King County and the city general fund. (Seattle City Council)

State legislation#

House Bill 1810 (2025)#

HB 1810 directs the Department of Commerce to study financial incentives for URM retrofits (tax modifications, exemptions, and support for schools and nonprofits) and the Emergency Management Division to create a statewide inventory of URM buildings. Preliminary report due June 2026; final report due September 2026. (SDCI Building Connections)

Other seismic legislation#

• Growth Management Act (RCW 36.70A) requires cities and counties to identify geologically hazardous areas, including seismic hazard zones, and establish protective regulations (MRSC)
• RCW 70.86 establishes earthquake standards for construction in Washington, requiring hospitals, schools, and public assembly buildings to withstand specified lateral forces (RCW 70.86)
• The Resilient Washington State framework, developed by the Emergency Management Council’s Seismic Safety Subcommittee, provides a roadmap for minimizing earthquake losses (DNR (PDF))

Preparedness programs#

Seattle Office of Emergency Management (OEM)#

OEM coordinates citywide earthquake preparedness, including guides for households, schools, and businesses. OEM recommends maintaining 7-10 days of emergency supplies – revised upward from the older 72-hour guideline after the Cascadia Rising exercises demonstrated that assistance could take days to reach affected areas. Washington state guidance now recommends two weeks. (Seattle OEM)

ShakeAlert earthquake early warning#

ShakeAlert, developed by the USGS in collaboration with the University of Washington and other partners, provides seconds of advance warning before strong shaking arrives. The system went live in Washington state in 2021 and sends Wireless Emergency Alerts to all phones for earthquakes of magnitude 5.0+ with significant expected shaking. (ShakeAlert | USGS ShakeAlert)

Community Emergency Hubs#

Seattle has over 136 designated gathering points throughout the city, with over 70 staffed by neighborhood volunteers. First formed in 2007 after a major windstorm, hubs are volunteer-run centers for post-disaster communication and response. Approximately 150 licensed amateur radio operators serve as the emergency communication backbone. (Seattle Emergency Hubs | Seattle OEM)

Seattle Neighborhoods Actively Prepare (SNAP)#

SNAP organizes neighbor-to-neighbor preparedness groups through OEM. Neighborhoods agree to work together following a major disaster, with assigned roles and designated meeting points. (Seattle OEM)

Cascadia Rising exercises#

The Cascadia Rising exercise series simulates a magnitude 9.0 CSZ earthquake and tsunami. The 2016 exercise brought together more than 20,000 federal, state, tribal, and local participants including military personnel across multiple states. (DVIDS) The 2022 follow-up focused on critical transportation and mass care services. A key finding was that assistance would take days, not hours, to reach affected areas – leading to the revised recommendation of two weeks of preparedness supplies.

Great Washington ShakeOut#

An annual statewide earthquake drill held each October. Over 1.2 million Washington residents registered for the 2025 drill. (MRSC)

Earthquake insurance#

Standard homeowners and renters insurance policies do not cover earthquake damage. Separate earthquake insurance must be purchased through private insurers. Washington has no state-run earthquake insurance authority equivalent to California’s CEA. (WA Insurance Commissioner)

Key facts:

• Only about 11% of Washington residents have earthquake insurance coverage (Seattle Times)
• Deductibles typically range from 10-25% of the coverage amount (WA Insurance Commissioner)
• Insurers may require property inspections or structural improvements (such as foundation bolting) before providing coverage (WA Insurance Commissioner)
• Earthquake insurance does not typically cover floods, tsunamis, or landslides triggered by earthquakes (WA Insurance Commissioner)

Advocacy organizations#

• ASAP! (Alliance for Safety, Affordability, and Preservation): The primary advocacy coalition pushing for mandatory URM retrofits in Seattle. A broad coalition of developers, property owners, preservationists, engineers, and neighborhood associations. ASAP! has proposed a Transfer of Development Rights credit program to fund retrofits.
• Alliance for Pioneer Square: Advocates for earthquake safety and historic preservation in Pioneer Square, home to a concentration of URM buildings.
• SCIDPDA (Seattle Chinatown International District Preservation and Development Authority): Conducts outreach on URM retrofit compliance, cost estimates, and financing for property owners in the Chinatown-International District and Pioneer Square.
• Seattle Emergency Hubs: Volunteer network organizing community-level disaster preparedness across Seattle’s neighborhoods.

Data sources#

USGS Earthquake Hazards Program#

National seismic hazard maps, earthquake probabilities, ShakeAlert data, and research on Pacific Northwest faults.

Access: USGS Earthquake Hazards | ShakeAlert

Pacific Northwest Seismic Network (PNSN)#

Operated by the University of Washington and University of Oregon, PNSN runs approximately 400 seismometers across Washington and Oregon. Provides real-time seismograms, earthquake catalogs, hazard maps, and information on notable earthquakes.

Access: PNSN

Washington DNR Geologic Hazard Maps#

Site class maps, liquefaction susceptibility maps, seismic design category maps, and active fault maps for all Washington counties. The DNR Seismic Scenario Catalog provides loss estimates for 20 earthquake scenarios including the Cascadia Subduction Zone, Seattle Fault, and Tacoma Fault.

Access: Geologic Hazard Maps | Seismic Scenarios

Seattle URM Building Inventory#

SDCI maintains an interactive map and dataset of all identified URM buildings in Seattle, including retrofit status.

Access: SDCI URM Program | URM Interactive Map (ArcGIS)

Seattle SHIVA Earthquake Hazard Assessment#

Seattle’s hazard identification and vulnerability analysis for earthquakes, covering fault sources, liquefaction zones, and expected damage scenarios.

Access: SHIVA Earthquake Assessment (PDF)

Washington State URM Dashboard#

Statewide inventory of known or suspected unreinforced masonry buildings, compiled from multiple data sources.

Access: WA URM Dashboard

Key statistics#

Sources: Seattle SDCI URM Program | USGS Earthquake Probabilities | Seattle OEM | PNSN | WA Insurance Commissioner

Related resources#

• Land Use & Planning Glossary – Terms like SEPA, EIS, and SDCI
• Waterfront & Pike Place Market – Viaduct removal, seawall rebuild, and Waterfront Park
• Environmental Justice & Equitable Development – Duwamish Valley, equity frameworks, and cumulative impacts
• Seattle OEM: Earthquake Hazards – City’s earthquake risk overview
• DNR: Earthquakes and Faults – Statewide seismic information

Last updated: February 2026