This section can help educate communities about the array of potential coseismic hazards for the Pacific Northwest. An earthquake is a sudden trembling motion caused by an abrupt release or strain on the tectonic plates that form the earth's crust. Faults on or near the plate boundaries slip when the rock exceeds its elastic limit causing earthquakes. A tsunami is one or a series of huge sea waves caused by an earthquake, submarine earthquake, volcanic eruption, landslide, or other large-scale disturbance of the ocean floor. Sometimes referred to incorrectly as tidal waves, tsunamis have nothing to do with tides.
Earthquakes can cause the soil to liquefy.
A landslide is the downward and outward movement of slope-forming material such as rocks, dirt, or mud due to gravity's forces. Earthquakes can trigger landslides causing severe damage to both the natural and man-made environment. For example, extensive mining in a place can cause subsidence to occur. Secondary Hazards Secondary hazards are triggered by an earthquake or seismic activity, and include such events as dam failures, fires, and oil or chemical spills. This section defines vulnerability and the vulnerabilities of ports and harbors.