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Los Angeles Times
12 hours ago
- Climate
- Los Angeles Times
An earthquake just off California's coast poses dire tsunami risk for many communities
SAN FRANCISCO — California does not often experience dangerous tsunamis, but there is one type of ocean surge some experts are increasingly concerned about. Near-shore tsunamis — those triggered by earthquakes just offshore — could pose a particularly dire risk for California's heavily populated coastal communities, according to experts, disaster modeling and local hazard plans. Depending on the strength and location of the quake, life-threatening waves could approach the coastline in as few as 10 minutes, perhaps not even enough time for an emergency alert to be issued, much less arrive on your cellphone. And it's a potential threat all along California's 840-mile coast, from the dense cities in the south to more remote reaches in the north. Data published in both the city and county of Los Angeles' hazard mitigation plans show how locally generated tsunamis could reach heights of up to 5 feet above the mean sea level in Marina del Rey; 7 feet in Manhattan Beach and San Pedro; 8 feet in Long Beach and the Santa Monica Pier; 9 feet in Malibu; and 30 feet on Catalina Island — depending on the fault that ruptures or where an underwater landslide is triggered. In Orange County, a magnitude 6.8 quake just offshore could bring a local-source tsunami to the coast in as little as 15 minutes, county documents say. A quake-triggered submarine landslide could inundate areas in Newport Beach — including Balboa Island, Balboa Peninsula and Lido Isle — and potentially surge so far inland up San Diego Creek that water approaches the 405 Freeway in Irvine. And in the San Francisco Bay Area, near-shore tsunami could cause waves to surge 4 feet above mean sea level at San Francisco's Aquatic Park, Alcatraz Island, Redwood City and Richmond; 5 feet in Alameda; 6 feet at San Francisco's Ocean Beach; 7 feet in Sausalito; 8 feet in Pacifica in San Mateo County; and 9 feet in Bolinas in Marin County, according to the California Geological Survey. Reginald Harrison, director of disaster preparedness and emergency communications for the city of Long Beach, said 'tsunamis are a rare but real threat to our community.' 'Unlike earthquakes, however, tsunamis provide natural warnings before they arrive,' Harrison said in a statement released ahead of Tsunami Preparedness Week. 'If you are near the beach when this occurs, you should move to higher ground as quickly as possible.' California is home to a number of communities where evacuating quickly could be immensely challenging. A study published in 2020 identified nine densely populated and particularly problematic places. They include Naples island in Long Beach; Oxnard Shores and southern Channel Islands Beach in Ventura County; the islands in Huntington Harbour; Balboa Island; Balboa Peninsula/Lido Isle; San Diego's Mission Beach peninsula; the Coronado peninsula, and Bay Farm Island in Alameda. Alameda is particularly vulnerable to tsunami. More than half its about 75,000 residents live in a designated hazard zone, and there are few exits from the community — which is split between Bay Farm Island (actually a peninsula) and the main Alameda island. However, officials there contend 'there is minimal risk of any significant tsunami occurring' from a local fault. Instead, they say, the greatest risk is from distant areas, which could produce tsunami of as much as 18 feet above sea level in Alameda. In other places, though, a near-shore tsunami could produce the highest waves. In Redondo Beach, for instance, a near-shore tsunami could bring waves of up to 11 feet above mean sea level, compared to 9 feet possible coming from a distant earthquake. Katie Eing, the emergency services coordinator for Newport Beach, estimated 45,000 people live in the potential local inundation zone, about half of the entire city's population. However, she noted many more visitors and workers could also be present, especially during tourist season. Eing said a near-shore tsunami could be devastating. The city's hazard mitigation plan cites a study from USC that estimates 'a potential submarine landslide anywhere along the steep Southern California offshore escarpment could generate a tsunami' that reaches an elevation of 30 feet to 33 feet above sea level. 'The concern with these local tsunami sources is that travel time between the local source of an earthquake and the arrival of the first waves along the coastline is estimated at 10 to 20 minutes, which does not allow much time for broadcasting of warnings and evacuation,' the report said. 'Several wave crests are likely, with the second and third waves likely to be higher than the first.' Evacuating all areas of the inundation zone, by comparison, would take hours, Eing estimated. That timeline is backed up by a 2015 study, which concluded a full evacuation of Newport Beach's tsunami-vulnerable areas could take almost 5 hours. Depending on the scenario, Eing said officials may recommend some people shelter-in-place rather than chance getting stuck in evacuation traffic at or below sea level. 'If it was a local-sourced earthquake… it's probably safer for [residents] to go to the third story,' she said. 'It's important to know where you live, if you're in the inundation zone.' The potential for chaos and confusion in an evacuation became all-too-apparent last December, when a magnitude 7 earthquake struck about 30 miles off the Humboldt County coast. An expansive tsunami warning arrived minutes later — sending alarms blaring on the cellphones of Californians from the North Coast through the San Francisco Bay Area, including Oakland, Berkeley and Alameda. Fortunately, only a small tsunami ended up materializing, just 2 inches high in Mendocino County. But the response and reaction shows plenty of room for improvement. Some of those who chose to evacuate didn't do so promptly, and there was widespread confusion whether evacuation was necessary at all. 'Many people questioned how a tsunami could enter the Bay and stated it must only be people on the coast who need to evacuate,' one person told the city of Berkeley in a survey. 'There was just tons of confusion all around, lots of complacency and not taking it seriously.' Another person complained that the only warning they got was the broad 'emergency alert' sent to all cellphones, as they weren't signed up for Berkeley's alert systems. As a result, 'we had no information at all about who should evacuate and who should not, access to a map, how much time we had,' that person wrote. Hesitation can be deadly. The 2011 magnitude-9.1 earthquake that struck near Japan spawned a tsunami that rose as high as 45 feet and reached the coast within just 30 minutes. More than 18,000 people died in the disaster, a toll exacerbated by an initial warning that underestimated the size of the tsunami before communications systems cut out entirely. Another issue, as documented by seismologist Lucy Jones in her book 'The Big Ones,' was the reluctance of some people to evacuate. That reluctance, as the Berkeley survey found, could be fueled by a lack of timely information. California's tsunami hazard map website didn't work during the alert period, for instance. In response, San Mateo County, just south of San Francisco, built its own online tsunami dashboard that lets residents and visitors plug in their location to see if they're in a hazard zone, as well as search for nearby safe places. Last December, Highway 1 was clogged with motorists trying to flee Pacifica. What many didn't realize is that in some vulnerable areas, heading just a few blocks inland was enough to safely be out of a tsunami's reach. Some evacuees also went in the wrong direction, driving from higher ground into lower-lying areas in an attempt to flee. Shruti Dhapodkar, director of emergency management for San Mateo County, heard from someone who lives in the coastal community of Montara — which is high enough in elevation that no tsunami would be expected to ever hit it. Yet that resident fled on Highway 1, directly into a low-lying area. 'I want to make this point very, very clear ... avoiding low-lying areas and moving to higher ground' is the objective, 'not necessarily getting in your car and coming over the hill,' Dhapodkar said. Understanding what areas of a city are threatened by tsunami are crucial — as is knowing where the safe areas are. If you're at the Santa Monica Pier, just head up above the bluffs, which are at about 100 feet above sea level. You don't need to run to Mount Baldy. In many parts of San Francisco, heading a few blocks away from the coast is enough to get to safety. The general advice is to evacuate by foot or on bicycle if possible to avoid traffic jams. But some officials acknowledge that could be a tough ask in car-crazy California. For more distant tsunamis, where hours may be available for an evacuation, scenarios can vary. 'For most of L.A., a huge chunk of our evacuation zone really is the beach and a couple of blocks inland,' said Jennifer Lazo, division chief of the innovation and technology division at the city's Emergency Management Department. But there are a number of areas in which people may need to drive out. In distant-source tsunami scenarios, firefighters and police officers would be dispatched to direct people out, Lazo said. Additional, crucial planning remains in the works. San Francisco says it needs to establish an evacuation strategy for people with disabilities, which it plans to complete by 2027. 'In areas where high ground is not immediately available, vertically evacuating and seeking refuge in tall buildings might be the best option for life safety, especially for people with disabilities or access and functional needs,' the city's hazards plan says. San Francisco also needs to develop and install signs on sidewalks and streets in low-lying waterfront areas to help people know where to go in case of tsunami and other coastal flood hazards, such as king tides, the city says. Some coastal areas have installed tsunami warning signs, but they're not ubiquitous. 'There is a lack of signage just throughout the entire state. Marin County — I'll speak to us — we definitely have limited signage throughout the county identifying tsunami inundation zones,' said Steven Torrence, Marin County's director of emergency management. The county Board of Supervisors doesn't have jurisdiction everywhere, he noted, but 'we need to make sure that the jurisdictions are clearly identifying these inundation zones.'
CBS News
25-03-2025
- Climate
- CBS News
San Mateo County launches online tool showing tsunami hazard zones
San Mateo County launched its new Tsunami Hazard Area Dashboard on Monday as part of a broader effort to better prepare for future tsunamis following last December's chaotic response to a regional tsunami warning . As part of California's Tsunami Preparedness Week, the county's Department of Emergency Management unveiled an online tool that allows residents to look at geographic areas designated as tsunami hazard zones before a tsunami happens. "We cannot control emergencies, but we can control our preparedness," said District 4 Supervisor Lisa Gauthier during a press conference unveiling the dashboard. On the morning of Dec. 5, 2024, San Mateo County residents received a cellphone notification from the National Weather Service warning them of a potential tsunami triggered by a magnitude 7.0 earthquake off the coast of Humboldt County. One hour later, the warning was canceled. The warning advised people in the tsunami hazard zone to retreat to higher ground. The tsunami hazard zone covered much of the county, including areas that were not actually at risk, according to District 3 Supervisor Ray Mueller. "Everyone in the county received a National Weather Service tsunami alert, even though not everyone was in danger," Gauthier said. The broad scope of the warning spurred many people along the coast to drive toward routes like state Highway 92 that move eastward. The influx of cars resulted in traffic jams along the few roadways that connect inland. "Many people ran to Highway 1, which is actually in the tsunami zone," Mueller said. "They got stuck in traffic when they could have just gone few blocks east." After gathering feedback from the community, the county's Department of Emergency Management identified areas of improvement to work on in preparation for future emergencies. The Tsunami Hazard Area Dashboard is one development intended to ameliorate preparedness and efficiency before and during a tsunami. The dashboard defines the exact areas in the county considered hazardous in the event of a tsunami. Specifying tsunami hazard zones minimizes the amount of people who need to evacuate, thus reducing traffic jams. The dashboard is a map of the county shaded in either green or yellow. Yellow zones, which are hazardous during tsunami, include parts of coastal towns like Half Moon Bay, Pescadero, El Granada and Pacifica. Along the San Francisco Bay, minimal portions of Burlingame, Foster City, Redwood City and East Palo Alto are also in the yellow zone. "On December 5, we heard so many stories about people who didn't know if their children were in safe locations or if their spouses were in safe locations," Mueller said. "They were traveling all over the coast in panic trying to figure out if they were safe and if who they loved were safe." The county also wanted to create its own resource since the California Department of Conservation's online dashboard crashed on Dec. 5 due to the magnitude of people trying to access the website. "People on the San Mateo County coast went to a state website to see if they were in a zone that could be impacted," Mueller said. "Because so many people were looking at that website, it actually failed ... When this event happens again in the future, should it happen again, we know that county resources will be backing that website." Other updates intended to bolster the county's preparedness for a tsunami include placing more warning signs in tsunami hazard zones. In several weeks, the county is planning to add high-low sirens to law enforcement vehicles that alert residents to evacuate during emergencies. People can sign up for SMC Alert , the county's mass notification system for communicating information during emergencies by going to the county's website and using the emergency services drop-down menu. Additional tsunami preparedness resources can be found online on the county's website, as well.
Yahoo
19-03-2025
- Climate
- Yahoo
Tsunami could flood ‘sizeable areas' of coastal Los Angeles County, experts say
Officials are cautioning residents to check whether they live in a tsunami zone ahead of Tsunami Preparedness Week, and there's a grim outlook for some of coastal SoCal should worse come to worst. The California Department of Conservation has released Tsunami Hazard Area maps and data that show the risk of a tsunami for coastal communities from the Mexico border to the Oregon state line. The most recent data for L.A. County was published in 2021 and indicates that a large tsunami could flood 'sizeable areas' of Marina del Rey and Long Beach to an elevation of 15 feet, according to Rick Wilson, head of the California Geological Survey's Tsunami Program. 'Flood levels for the Port of Los Angeles and the Port of Long Beach could reach elevations of 12 to 15 feet, which would inundate almost all of the land in the ports and some of the surrounding communities,' Wilson stated. 'Local officials have indicated that if both ports were shut down for one day, the economic loss to the county would be over $1 billion.' Tsunami Hazard Area maps can be viewed for Los Angeles, Orange and Ventura counties. To view all California counties, click here. California's Tsunami Preparedness Week is March 22 through March 30. Copyright 2025 Nexstar Media, Inc. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.
