Update: After the 8.2-magnitude earthquake struck the coast of Chile April 1, the Los Angeles Times reported small tsunami waves and "unusual water movement" arrived in La Jolla. The article states "the National Weather Service ended a tsunami advisory for the state of Hawaii around 7:25 a.m. (Wednesday). But the first waves connected to the South American earthquake to strike California may have hit La Jolla hours earlier, said Bill Knight, an oceanographer with the National Tsunami Warning Center based in Alaska." No tsunami warning has been issued for California.
By Ashley Mackin
Several San Diego safety and public service organizations — including the San Diego County Office of Emergency Services, San Diego Office of Homeland Security, City Council District 1 and San Diego Lifeguards — gathered March 26 at Kellogg Park in La Jolla Shores to recognize Tsunami Awareness Week, March 23-29, and announce the distribution of new maps that outline the risk of tsunami, as well as suggestions on what to do in the event of one.
“San Diego has 70 miles of coastline and it’s important for San Diegans to understand our risk for tsunami,” said Holly Crawford, the county’s Director of Emergency Services. “Today, we mailed 33,000 brochures to homes and businesses that tell — not only what to do before, during and after a tsunami — but depict a map of the worst tsunami-prone zones and potential evacuation routes where residents can flee in a case of a tsunami.”
Two kinds of tsunamis
San Diego susceptible to both near- source and distant-source tsunamis, Crawford explained. “In the event of an earthquake right off the coast (a near- source tsunami), we might only have 10- 15 minutes to respond. So we want people to know, if the earth shakes for 20 seconds ... you need to leave the coast, go to a place that’s at least 100 feet above sea level or at least two miles inland.”
A distant-source tsunami, which would take longer to reach San Diego and therefore allow more time to respond, is a more likely threat.
Senior Geological Engineer from the California Geological Survey Rick Wilson explained large magnitude earthquakes — such as the 9.2-magnitude earthquake off the coast of Alaska that generated a tsunami that reached California in 1964 — are more likely to happen in areas like Alaska and Japan than they are in southern California. However, the tsunamis generated by these larger earthquakes have the ability to travel farther.
“From a distant-source perspective, a tsunami generated around the Pacific could strike our shores within hours,” he said.
Knowing the signs of a possible tsunami is key. In addition to being aware of the connection between significant earthquakes and possible tsunamis, Wilson said one sign a tsunami might be coming is water receding from the coastline. He said people often run toward the water to see the rocks and catch the fish that become visible, which is contrary to the consistent advice of getting away from the coast.
UCSD seismology professor Gabi Laske added that water can recede for up to 15 minutes before a tsunami hits. “Unfortunately, not every tsunami starts with water receding,” she said. “But if you see water receding for 15 minutes, you gotta run.”
Crawford strongly recommends signing up for the Alert San Diego system found at ReadySanDiego.org so citizens can be notified of any emergency.
“The county of San Diego wants to be able to reach you on your mobile phone to tell you to evacuate. But we cannot reach you unless you register for ... our mass notification system,” she said. When registering a phone number, a home address must also be registered so individuals will only be notified of disasters in their area or ones that they should be aware of.
In the event people are on the beach and there is a tsunami threat, lifeguards will use a device called long-range acoustic device (LRAD) to notify people across a far distance. Different from a PA system, which broadcasts wide across but not far out, LRAD devices beam a narrow, but farther reaching message.
During the Shores demonstration, Service Lieutenant John Sandmeyer sent a reduced-power test message to the lifeguard tower, approximately 500 feet away, and to a lifeguard truck a third of a mile away. Both recipients confirmed they heard the transmission. When turned to full power, Lt. Sandmeyer said a message sent from La Jolla Shores could be heard at La Jolla Cove.
However, Sandmeyer said those outside the “beam” might not hear the message due to the mechanics of the device, and to always listen to authorities such as lifeguards and police. These authorities would not only tell when to evacuate, but also when it’s safe to return, a notion Laske said is ever important.
“The common perception is, with a tsunami, it’s one big wave and the show is over, but that is not the case,” she said. “It’s a series of waves and it might be that the later waves can be higher than the first ones and it can go on for hours. In the 2011 Japan tsunami, it took days for the ocean to calm down.”
Eighth-grade students from the Old Town Academy attended the presentation and participated in an evacuation exercise. Wilson encouraged the students to be knowledgeable about tsunamis.
“Though tsunamis are rare, we can still do a lot to prepare for them,” he said. “We are going to face a tsunami at some time in the future, the important thing is to be prepared.”
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What’s a Tsunami?
■ A tsunami (from Japanese “harbor wave”) is a series of huge water waves caused by the displacement of a large volume of a body of water. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.
■ Tsunamis cause damage by two mechanisms: The smashing force of a wall of water travelling at high speed, and the destructive power of a large volume of water draining off the land and carrying a large amount of debris with it.