New Tsunami Hazard Map Shows Santa Monica's Vulnerable Areas
A sign points to the direction of the evacuation route in the event of a tsunami warning, on Main Street, in Santa Monica, Calif., on Thursday, April 29, 2021. (Marco Pallotti | The Corsair)
The California Geological Survey (CGS) released updated hazard area maps that show more regions within Santa Monica, Venice, Marina Del Rey and the Port of Long Beach are vulnerable to tsunamis than previously estimated in 2009. The interactive maps were released in March during California’s Tsunami Preparedness Week, a campaign to educate residents of coastal regions that may one day be impacted by tsunamis.
Tsunamis are a series of waves most commonly caused by an earthquake beneath the seafloor, or by landslides. Two types of tsunamis exist — distant tsunamis and local tsunamis, based on where the earthquake or landslide activity occurs that then generates the waves.
Santa Monica College (SMC) geology professor Dr. Lisa Collins welcomed the government’s efforts to bring awareness to these unpredictable phenomena so people can plan accordingly. “In the last decades, what we thought were areas that are hazardous have changed, in part because of climate change," said Collins. "The sea level is rising more rapidly than expected."
The 2011 Tōhoku earthquake caused tsunami waves to reach California, though only in the northern part of the state. According to Collins, the reason Southern California is prone to different tsunamis than Northern California is because of the Channel Islands, a group of eight islands off the coast of California between Santa Barbara and Los Angeles counties. "They actually help protect [Southern California]," said Collins. "[A] tsunami coming from Japan has to go around the islands first, and so it dissipates or loses energy as it goes around the islands."
When considering a worst-case scenario, the CGS calculates that it would take a 9.3 magnitude earthquake off the Aleutian trench near Alaska to trigger a distant tsunami in Southern California. When that occurs, a warning would be distributed by the Emergency Alert System, the United States' public warning system, and individuals might have 5-6 hours to evacuate.
Local tsunamis originate from a source in close proximity to the coast. Waves could reach nearby shores within minutes and with very little warning. An earthquake at faults near Catalina Island, which lies about 22 miles off the coast of Los Angeles, or landslides on the Portuguese Bend in Palos Verdes, Calif., could send tsunami waves to Southern California.
Dr. Collins noted that one often overlooked threat is underwater landslides off the coast of Long Beach, Calif. “We have evidence that these submarine landslides have happened in the past.” In the event of an earthquake, sediments deposited by the Los Angeles River "will slump or fall down," said Collins. "All that water that's above them suddenly drops down and creates a wave that could create a tsunami."
Tsunami warning signs include strong earthquakes that last extended periods of time, over twenty seconds, a loud roaring sound coming from the ocean, or a sudden rise or fall of the ocean. Those who find themselves in a hazard zone should move to higher ground on foot, since roads and bridges may be damaged. “There’s no harm in getting to higher ground if nothing happens,” said Collins. “The harm is if you don't evacuate and then there is a tsunami.”
The CGS maps allow users to determine if they live, work or play in a tsunami hazard zone and provide evacuation routes. If a tsunami warning has been issued, local radio or television stations will provide additional information, and the public is urged to follow the instructions of emergency personnel. The City of Santa Monica provides an alert notification system, SM Alerts, to share emergency updates via phone, email, or text message.
Tsunamis may seem rare and unlikely, but when considering the vast coastal land use and popularity of recreational activity on the beach, familiarizing the community of the hazards could save many lives.
