Cannon Beach's location along the Oregon Coast makes it susceptible to earthquakes, especially a Cascadia Subduction Zone earthquake. The extent of the earthquake hazard includes the entire community of Cannon Beach, although damage from an earthquake may be more severe in the downtown area where buildings are old and sit on fill that has liquefaction potential.
Clatsop County's Natural Hazards Mitigation Plan adequately describes the causes, characteristics, and location of earthquake hazards for the region. The County's Plan additionally identifies all previous occurrences that have affected the City. It is difficult to estimate recurrence intervals, but the state has experienced seven Cascadia Subduction Zone (CSZ) events in the last 3500 years - some of which were probably as large as magnitude (M) 9. These events are estimated to have an average recurrence interval between 500 and 600 years, although the time interval between individual events ranges from 150 to 1000 years. The last CSZ event occurred approximately 300 years ago. Scientists estimate that there is a 10-20% probability that a subduction zone earthquake will occur within the next 50 years. Based on this information, Clatsop County estimates a 'high probability than an earthquake will occur in the future. Cannon Beach agrees.
The Department of Geology and Mineral Industries developed earthquake hazard maps (See links below). The figures illustrate the location of the amplification, liquefaction, earthquake-induced landslide, and relative earthquake hazards in Cannon Beach, Seaside, and Gearhart.
Clatsop County estimates a 'high' vulnerability to earthquake hazards, meaning more than 10% of the population or regional assets would be affected by a major emergency or disaster. As shown by the figures above, the City has a moderate risk of amplification, and a very high risk of liquefaction. The majority of the City's developed lands are located in Zone A - the highest hazard area for earthquakes. Additionally, as described above on page 7, about 53% of the Citys housing stock was built prior to 1980, before stronger seismic building codes were put into place. The combination of these hazards makes Cannon Beach extremely vulnerable to high magnitude earthquake events.
In 2006, DOGAMI conducted a seismic needs assessment for public school buildings, acute inpatient care facilities, fire stations, police stations, sheriff's offices and other law enforcement agency buildings. Buildings were ranked for the "probability of collapse" due to the maximum possible earthquake for any given area. Within Cannon Beach, the following buildings were rated as 'moderate' or 'high'. No buildings in Cannon Beach were assigned the 'very' high rating.
- Cannon Beach Police Department; moderate
In addition to the structures listed above, the Citys infrastructure is highly vulnerable to a severe earthquake event. Sewer lines, water lines, power lines, water tanks, reservoirs, and cell towers are vulnerable assets. The City would expect significant damage to roads and bridges following a Cascadia Subduction Zone event, as well as deaths and severe injuries region-wide. Education and outreach regarding earthquakes (and a resultant tsunami) is an ongoing endeavor in Cannon Beach. Additional community impacts are adequately described within the County's Earthquake Hazard Annex.