A tsunami is a series of waves or surges most commonly caused by an earthquake beneath the sea floor. Tsunamis can cause great loss of life and property damage in coastal areas. Very large tsunamis can cause damage to coastal regions thousands of miles away from the earthquake that caused them.
When should I evacuate?
Evacuation should not be automatic. Before evacuating you should determine if you are in a hazard zone and consider possible hazards that may exist along your evacuation route. Visit www.tsunami.ca.gov to find out if you live, work, or play in a tsunami hazard zone.
COUNT how long the earthquake lasts. If you feel more than 20 seconds of very strong ground shaking and are in a tsunami hazard zone, evacuate as soon as it is safe to do so. If you are on the beach or in a harbor and feel an earthquake - no matter how small - immediately move inland or to high ground.
GO ON FOOT. Roads and bridges may be damaged. Avoid downed power lines. If evacuation is impossible, go to the third or higher floor of a sturdy building or climb a tree. This should only be used as a last resort.
If you hear that a tsunami warning has been issued but did not feel an earthquake, get more information. Listen to the radio, television or other information sources and follow the instructions of emergency personnel.
If you are outside of a tsunami hazard zone, take no action. You are safer staying where you are.
There are two ways to find out if a tsunami may be coming. These natural and official warnings are equally important. Respond to whichever comes first.
Natural warning. Strong ground shaking, a loud ocean roar, or the water receding unusually far exposing the sea floor are all nature's warnings that a tsunami may be coming. If you observe any of these warning signs, immediately go to higher ground or inland. A tsunami may arrive within minutes and may last for eight hours or longer. Stay away from coastal areas until officials announce that it safe to return.
Official warning. You may hear that a Tsunami Warning has been issued. Tsunami warnings might come via radio, television, telephone, text message, door-to-door contact by emergency responders, NOAA weather radios, or in some cases by outdoor sirens. Move away from the beach and seek more information on local radio or television stations. Follow the directions of emergency personnel who may request you to evacuate beaches and low-lying coastal areas. Use your phone only for life-threatening emergencies.
Seismic Hazard Zones (SHZs) identify areas that may be prone to liquefaction or landsliding triggered by earthquake shaking. Liquefaction is a temporary loss of strength in the ground that can occur when certain water saturated soils are shaken during a strong earthquake. When this occurs buildings can settle, tilt, or shift. Landsliding can occur during an earthquake where shaking reduces the strength of the slope. These hazards can usually be reduced or eliminated through established engineering methods. The law requires that property being developed within these zones be evaluated to determine if a hazard exists at the site. If so, necessary design changes must be made before a permit is granted for residential construction. Being in an SHZ does not mean that all structures in the zone are in danger. The hazard may not exist on each property or may have been mitigated. Mapping new SHZs in urban and urbanizing areas is ongoing statewide. Current zones, as established by the California Geological Survey, are indexed at www.conservation.ca.gov/cgs.
Earthquake Fault Zones (EFZs) recognize the hazard of surface rupture that might occur during an earthquake where an active fault meets the earth's surface. Few structures can withstand fault rupture directly under their foundations. The law requires that within an EFZ most structures must be set back a safe distance from identified active faults. The necessary setback is established through geologic studies of the building site. EFZs are narrow strips along the known active surface faults wherein these studies are required prior to development. Being located in an EFZ does not necessarily mean that a building is on a fault. Most of the important known faults in California have been evaluated and zoned, and modifications and additions to these zones continue as we learn more.