Tsunami Tips

Tsunamis, while unlikely to impact Diamond Heights physically, are a valid concern for those who spend time, have family or friends, or own property near the coast. If you or any loved ones are likely to be affected, plan ahead, learn your evacuation routes, and evaluate your insurance needs in case of tsunami damage.

Seismic activity in the far northern Pacific is often of the subduction type, with tectonic plates sliding under each nother. This can generate tsunamis thousands of miles away. Tsunamis from major earthquakes in Japan, Alaska, or the Cascade region of the Pacific Northwest can strike low-lying, northwest- or west-facing California coastal areas. Emergency officials may issue warnings hours ahead of a distant tsunami’s arrival.

The San Andreas Fault, where tectonic plates slip past rather than under each other, is less likely to create tsunamis. However, it can, and we may have little or no advance warning.

In California, the north coast around Crescent City is vulnerable. Half Moon Bay, Santa Cruz, and Monterey Bay, which are open to the ocean, have had damage to vessels, docks, and buildings in recent decades. Even vessels and structures within San Francisco Bay may be at risk from rising tides confined within the Bay.

TSUNAMI EMERGENCY

A major quake in the Pacific may prompt tsunami warnings in the Bay Area. If you hear or read such a warning, do not go to the beach or Bay to “sightsee.” Incoming tsunamis and resulting panics have killed curious bystanders around the world. Crowds can also hinder emergency operations.

A tsunami produced by a quake on the San Andreas Fault may arrive within a few minutes. If you are near coastal or Bay waters and feel a strong quake lasting 20 seconds or more, do not wait for a siren, radio, website, or other warning. Get away from the shore and onto higher ground as soon as it is safe to move. In many coastal areas, you will see signs reading “Tsunami Evacuation Route” with an ocean wave graphic. Depending on the location and traffic conditions, it may be faster and safer to evacuate on foot than to try to drive away.

Some of the preceding information can be found at the following websites, along with more detailed coverage of tsunami preparation, emergency response, California inundation zones, and historic tsunami case studies.

• City and County of San Francisco preparedness website:
  www.72hours.org
• City of Pacifica tsunami plan, including pre-planning advice and a safety brochure, much of which is applicable to San Francisco:
  www.cityofpacifica.org/depts/police/natural_disasters/tsunami.asp
• California Department of Conservation:
  www.consrv.ca.gov/cgs/geologic_hazards/Tsunami/Inundation_Maps/Pages/Statewide_Maps.aspx
• United States Geological Survey:
  walrus.wr.usgs.gov/tsunami/