'That was awesome!' California's earthquake early warning system let many know about today's temblor
Monday's magnitude 5.2 temblor marked another success for California's earthquake early warning system, with users in some areas saying they received alerts on their phones before they felt shaking.
The alerts in some cases provided pivotal seconds of lead time — a heads-up that could be critical in the event of a major earthquake.
'That was awesome! GREAT EARLY WARNING!!!' a resident told the USGS' ShakeAlert social media account on X. 'I got the alert on my phone near downtown San Diego several seconds before the primary [shaking] wave hit. WELL DONE!'
The temblor was centered near the San Diego County mountain town of Julian.
Because shaking from a quake travels at the speed of sound through rock, slower than the speed of modern communications systems, alerts sounded in some parts of Los Angeles before the shaking had even reached the city. No major damage or injuries were reported.
The ShakeAlert earthquake warning system — which is operational in California, Oregon and Washington state — is run by the U.S. Geological Survey. The system relies on a vast array of seismic sensors to detect shaking as soon as it happens. That information is then sent to computers to determine whether and where to send an alert.
People in Camarillo, Manhattan Beach, Palm Springs, Riverside, the San Diego neighborhood of Rancho Peñasquitos, Santa Ana and southern Orange County said they got the earthquake early warning before the shaking started, according to posts on social media and interviews with local news outlets.
"Corona Del Mar here. Got the alert about 5-10 seconds before a big jolt. Great service," one resident posted on X.
"I got the alert 1 second before I felt it! I'm in Palm Springs! I'm extremely impressed," another user added.
Read more: California earthquake early warning system: How to get it now
"SHAKE ALERT DID IT!! Had phone in hand ... and I had 5+ seconds to respond," wrote another.
Geologists at the California Geological Survey's office in Los Angeles also received early warning notifications on their phones "so we were prepared for some shaking," one scientist posted on social media.
One of the fastest ways people can get earthquake early warnings is by downloading MyShake, a free app developed by UC Berkeley that provides alerts in partnership with the USGS and the California Governor's Office of Emergency Services. The app can be downloaded to Android devices as well as on iPhones, iPads and Mac computers.
Android phones also have a built-in earthquake early warning app.
More than half a million people in California got early warnings through MyShake on Dec. 5 for a magnitude 7 earthquake that struck 30 miles off the Humboldt County coast; and on Dec. 9 for a magnitude 5.7 earthquake centered about 50 miles southeast of Reno, which was widely felt across Central California.
San Diego County also offers the free SD Emergency app, which includes the ShakeReadySD earthquake early warning tool.
Read more: California earthquake warning app is now available on more devices. Here's how to get it
Some Angelenos who got the alert said it elevated what is typically a fairly normal situation — especially for longtime residents. One person posted on X that she "was, frankly, scared" after getting the "Drop. Cover. Hold on" directions from the alert, though she's lived through dozens of other quakes.
That feeling, however, can lessen as people become accustomed to the alerts. For some, it's helpful to know that the shaking they're feeling is actually an earthquake, so they can take protective actions such as dropping under a desk, covering and holding on.
Earthquake early warnings are now commonplace in seismically active areas around the world, including in Japan, Mexico and Taiwan.
Android phones and those with the MyShake or ShakeReadySD apps installed have the lowest threshold for earthquake early warnings. They're set to trigger alerts if a quake is estimated at magnitude 4.5 or higher and the intensity of shaking at the phone's location is expected to be 'weak' — defined as Level 3 on the Modified Mercalli Intensity Scale.
Shaking of that intensity would be noticeable to people indoors, especially on the upper floors of a building, and may cause cars to rock slightly. Some people indoors might liken the feeling to vibrations from a passing truck.
Read more: California's earthquake revolution: Early-warning systems make strides, issuing more than 5 million alerts
People who don't have smartphones or haven't installed early warning apps can still get alerts on their cellphones — but only when a higher magnitude or greater level of shaking is projected at their location. Those alerts are sent through the Wireless Emergency Alert system, similar to Amber Alerts.
One downside to relying on the Wireless Emergency Alerts, however, is that they provide less information than an app-generated alert.
There is a setting you can change on your iPhone to improve the speed, accuracy and reliability of emergency alerts, Apple says. To do that, you can turn on 'local awareness' by going to settings, then notifications; scrolling down to 'Government Alerts,' then tapping 'Emergency Alerts' and navigating to the option.
On its website, MyShake suggests opening the app every month or so to keep it 'fresh and ready to receive alerts. Not using the app for a prolonged period might cause the app to be put into deep sleep.'
One easy way to do this, MyShake suggests, is to click on the app when it notifies you — without any urgent, alarming warning sounds — of a significant earthquake somewhere around the world, which typically happens every two weeks. 'By tapping on this notification, and opening the MyShake app, you can keep the app fresh, and not have to rely on your own reminders.'
MyShake is now available in six languages: English, Spanish, Tagalog, Korean, Vietnamese and Chinese — the last voiced in Mandarin, and using traditional characters. MyShake will use the first language that it supports from your device's language and region settings, but on an iPhone you can change the language by going to settings, then apps, and selecting MyShake before choosing a preferred language.
Times staff writer Grace Toohey contributed to this report.
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This story originally appeared in Los Angeles Times.
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Yahoo
2 hours ago
- Yahoo
California tsunami: Here's where damage and casualties could be the worst
Tsunamis pose a risk to the entire California coast. But should a major one strike, how bad could it be? A single tsunami likely won't cause the worst-case scenario for every region. But in total, more than 680,000 Californians are in a tsunami hazard area during the daytime. And in all, $12.6 billion in damage is possible across California's 20 coastal and bayside counties — a figure that doesn't include damage to ports, harbors, roads, essential facilities or other infrastructure. There are two main types of scenarios for a tsunami. The first, a "distant-source" tsunami, comes from far away, like one spawned by a major earthquake in Alaska. That would provide an extensive warning — six hours for L.A. and five hours for San Francisco — but could produce the highest level of inundation for large swaths of the state. Then there are "near-source" tsunamis, which can wash ashore in as little as 10 minutes following a nearby earthquake — leaving little time for a notice or evacuation. Here are some scenarios for different parts of California. Unless otherwise mentioned, figures are from the California Tsunami Program, which is run by the California Governor's Office of Emergency Services and the California Geological Survey. Read more: These California coastal cities face heightened flood danger from tsunami, data show Distant-source tsunami: More than 350 people could die or be injured along the Southern California coast if people wait to evacuate half an hour after an official evacuation warning is given. That includes about 200 casualties in Los Angeles County, roughly 80 in San Diego County, 60 in Orange County and about a dozen in Ventura County. A hypothetical magnitude 9.3 earthquake from Alaska — similar in scale to the monstrous 1964 tsunami-generating temblor — would offer six hours of warning; large temblors from Chile could provide 13 hours of warning. The maximum projected distant-source tsunami could bring waves of 15 feet above the mean sea level to Marina del Rey, the Santa Monica Pier, Naples and Alamitos Bay; 14 feet elsewhere in other parts of Long Beach; 10 feet at Manhattan Beach, San Pedro and the ports of Los Angeles and Long Beach; 9 feet in Malibu, Redondo Beach and Palos Verdes Hills; and 8 feet at Leo Carrillo State Beach. Those estimates were issued by the California Geological Survey and published in the city of Los Angeles' hazard mitigation plan. Damage estimate from distant-source tsunami: More than $1.4 billion. Near-source tsunami: Los Angeles could see a tsunami move from its source to coastal areas in as few as 10 or 15 minutes, the city's tsunami plan warns. According to public documents, depending on the fault that ruptures, or where an underwater landslide is triggered, there could be locally generated tsunami heights of 30 feet in Avalon on Catalina Island; 24 feet at Palos Verdes Hills; 18 feet in Two Harbors; 11 feet in Redondo Beach; 9 feet in Malibu; 8 feet in Long Beach and the Santa Monica Pier; 7 feet in Manhattan Beach and San Pedro; 5 feet in Marina del Rey; and 4 feet at Leo Carrillo State Beach. In the city of Los Angeles, officials say that the most catastrophic scenario would involve an underwater landslide triggered by an earthquake, because "we wouldn't know that that landslide would occur until the wave arrives," said Jon Brown, assistant general manager for the city's Emergency Management Department. Other L.A. County areas with considerable vulnerability include the ports, as well as San Pedro and Long Beach. The city of Los Angeles has an estimated 23,000 residents in the tsunami hazard area. In Long Beach, the number is 31,000. Read more: The tsunami that battered Santa Cruz highlights the threat facing California's coast Distant-source tsunami: More than 230 people could die or be injured if people wait half an hour to evacuate after an official warning is given. Santa Cruz County could see more than 130 casualties; San Luis Obispo County, about 80. The estimated potential casualty tolls could be 16 in Monterey County and seven in Santa Barbara County. Damage estimate from distant-source tsunami: More than $3.5 billion. Near-source tsunami: Santa Cruz and Monterey counties could see a tsunami within minutes following quake-triggered underwater landslides, documents from both counties say. "Even a moderate earthquake could cause a local-source tsunami from submarine landsliding in Monterey Bay," public documents say. A near-source tsunami could bring waves of up to 15 feet above the mean sea level in the city of Marina, 9 feet at the Salinas River; 8 feet at the Pajaro River and Sand City, just northeast of Monterey, and 6 feet at Moss Landing, according to data published in Monterey County's hazard mitigation plan. Such devastation would not be unprecedented. A large earthquake in the Santa Barbara area in 1812 resulted in a tsunami "that wiped out many coastal villages and destroyed ships in the harbor," according to the U.S. Geological Survey. And 7-foot waves resulted from a tsunami in 1927, generated by an earthquake about 5 miles west of the Santa Barbara County coast, according to the California Geological Survey. The USGS said there's evidence of deposits from underwater landslides offshore of Santa Barbara dating back over 160,000 years, which suggests that "future earthquakes could cause large submarine landslides and devastating tsunamis." Read more: Can a tsunami happen in Southern California? What should you do about it? Distant-source tsunami: More than 1,300 people could die or be injured if people wait half an hour to evacuate after an official warning is given. About 500 of them could be in San Francisco; about 300 apiece in San Mateo and Marin counties; nearly 200 in Alameda County and 33 in Contra Costa County. Just north of the region, in Mendocino County, five people could die or be injured in that scenario. A hypothetical tsunami-generating earthquake in Alaska could provide 5 hours of warning; one from Chile could provide 13 hours of warning. The maximum projected distant-source tsunami could result in tsunami of 32 feet above mean sea level in San Francisco's Ocean Beach; 31 feet in Pacifica in San Mateo County; 27 feet in Bolinas in Marin County; 18 feet in Alameda; 14 feet in Sausalito and San Francisco's Aquatic Park; 13 feet on Alcatraz Island; and 11 feet in Richmond and Treasure Island, according to the California Geological Survey. Damage estimate from distant-source tsunami: More than $6.5 billion. Near-source tsunami: In Northern California, a near-source tsunami could generate a tsunami of 9 feet above sea level in Bolinas; 8 feet in Pacifica; 7 feet in Sausalito; 6 feet at Ocean Beach; 5 feet in Alameda; and 4 feet at Alcatraz Island, Treasure Island, Aquatic Park, Redwood City and Richmond. Read more: The California tsunami danger is real. The 7.0 earthquake is wake-up call to prepare Cascadia scenario: Given its proximity to the Cascadia subduction zone, Del Norte County — the state's northernmost coastal region — is perhaps more exposed to tsunami risk than any other part of California. If people wait 10 minutes after an earthquake to evacuate — the shaking itself would be the warning to flee — more than 3,150 are at risk of being killed or injured by tsunami in Del Norte County, and more than 720 would be at risk in neighboring Humboldt County. Flooding could reach up to 30 feet above the average high tide along the outer coast of Humboldt Bay and the Eureka area, and up to 50 feet toward Crescent City. "A large quake generated by the Cascadia subduction zone could create waves twice as large as the 1964 event, especially in Crescent City," Rick Wilson, a former head of the California Geological Survey tsunami program, said in a statement. Damage estimates: Del Norte County, which is home to Crescent City, could see more than $1 billion in damage. Humboldt County, home to Eureka, could see $22 million. Sign up for Essential California for news, features and recommendations from the L.A. Times and beyond in your inbox six days a week. This story originally appeared in Los Angeles Times.
Los Angeles Times
3 hours ago
- 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.'
Los Angeles Times
3 hours ago
- Los Angeles Times
California tsunami: Here's where damage and casualties could be the worst
Tsunamis pose a risk to the entire California coast. But should a major one strike, how bad could it be? A single tsunami likely won't cause the worst-case scenario for every region. But in total, more than 680,000 Californians are in a tsunami hazard area during the daytime. And in all, $12.6 billion in damage is possible across California's 20 coastal and bayside counties — a figure that doesn't include damage to ports, harbors, roads, essential facilities or other infrastructure. There are two main types of scenarios for a tsunami. The first, a 'distant-source' tsunami, comes from far away, like one spawned by a major earthquake in Alaska. That would provide an extensive warning — six hours for L.A. and five hours for San Francisco — but could produce the highest level of inundation for large swaths of the state. Then there are 'near-source' tsunamis, which can wash ashore in as little as 10 minutes following a nearby earthquake — leaving little time for a notice or evacuation. Here are some scenarios for different parts of California. Unless otherwise mentioned, figures are from the California Tsunami Program, which is run by the California Governor's Office of Emergency Services and the California Geological Survey. Distant-source tsunami: More than 350 people could die or be injured along the Southern California coast if people wait to evacuate half an hour after an official evacuation warning is given. That includes about 200 casualties in Los Angeles County, roughly 80 in San Diego County, 60 in Orange County and about a dozen in Ventura County. A hypothetical magnitude 9.3 earthquake from Alaska — similar in scale to the monstrous 1964 tsunami-generating temblor — would offer six hours of warning; large temblors from Chile could provide 13 hours of warning. The maximum projected distant-source tsunami could bring waves of 15 feet above the mean sea level to Marina del Rey, the Santa Monica Pier, Naples and Alamitos Bay; 14 feet elsewhere in other parts of Long Beach; 10 feet at Manhattan Beach, San Pedro and the ports of Los Angeles and Long Beach; 9 feet in Malibu, Redondo Beach and Palos Verdes Hills; and 8 feet at Leo Carrillo State Beach. Those estimates were issued by the California Geological Survey and published in the city of Los Angeles' hazard mitigation plan. Damage estimate from distant-source tsunami: More than $1.4 billion. Near-source tsunami: Los Angeles could see a tsunami move from its source to coastal areas in as few as 10 or 15 minutes, the city's tsunami plan warns. According to public documents, depending on the fault that ruptures, or where an underwater landslide is triggered, there could be locally generated tsunami heights of 30 feet in Avalon on Catalina Island; 24 feet at Palos Verdes Hills; 18 feet in Two Harbors; 11 feet in Redondo Beach; 9 feet in Malibu; 8 feet in Long Beach and the Santa Monica Pier; 7 feet in Manhattan Beach and San Pedro; 5 feet in Marina del Rey; and 4 feet at Leo Carrillo State Beach. In the city of Los Angeles, officials say that the most catastrophic scenario would involve an underwater landslide triggered by an earthquake, because 'we wouldn't know that that landslide would occur until the wave arrives,' said Jon Brown, assistant general manager for the city's Emergency Management Department. Other L.A. County areas with considerable vulnerability include the ports, as well as San Pedro and Long Beach. The city of Los Angeles has an estimated 23,000 residents in the tsunami hazard area. In Long Beach, the number is 31,000. Distant-source tsunami: More than 230 people could die or be injured if people wait half an hour to evacuate after an official warning is given. Santa Cruz County could see more than 130 casualties; San Luis Obispo County, about 80. The estimated potential casualty tolls could be 16 in Monterey County and seven in Santa Barbara County. Damage estimate from distant-source tsunami: More than $3.5 billion. Near-source tsunami: Santa Cruz and Monterey counties could see a tsunami within minutes following quake-triggered underwater landslides, documents from both counties say. 'Even a moderate earthquake could cause a local-source tsunami from submarine landsliding in Monterey Bay,' public documents say. A near-source tsunami could bring waves of up to 15 feet above the mean sea level in the city of Marina, 9 feet at the Salinas River; 8 feet at the Pajaro River and Sand City, just northeast of Monterey, and 6 feet at Moss Landing, according to data published in Monterey County's hazard mitigation plan. Such devastation would not be unprecedented. A large earthquake in the Santa Barbara area in 1812 resulted in a tsunami 'that wiped out many coastal villages and destroyed ships in the harbor,' according to the U.S. Geological Survey. And 7-foot waves resulted from a tsunami in 1927, generated by an earthquake about 5 miles west of the Santa Barbara County coast, according to the California Geological Survey. The USGS said there's evidence of deposits from underwater landslides offshore of Santa Barbara dating back over 160,000 years, which suggests that 'future earthquakes could cause large submarine landslides and devastating tsunamis.' Distant-source tsunami: More than 1,300 people could die or be injured if people wait half an hour to evacuate after an official warning is given. About 500 of them could be in San Francisco; about 300 apiece in San Mateo and Marin counties; nearly 200 in Alameda County and 33 in Contra Costa County. Just north of the region, in Mendocino County, five people could die or be injured in that scenario. A hypothetical tsunami-generating earthquake in Alaska could provide 5 hours of warning; one from Chile could provide 13 hours of warning. The maximum projected distant-source tsunami could result in tsunami of 32 feet above mean sea level in San Francisco's Ocean Beach; 31 feet in Pacifica in San Mateo County; 27 feet in Bolinas in Marin County; 18 feet in Alameda; 14 feet in Sausalito and San Francisco's Aquatic Park; 13 feet on Alcatraz Island; and 11 feet in Richmond and Treasure Island, according to the California Geological Survey. Damage estimate from distant-source tsunami: More than $6.5 billion. Near-source tsunami: In Northern California, a near-source tsunami could generate a tsunami of 9 feet above sea level in Bolinas; 8 feet in Pacifica; 7 feet in Sausalito; 6 feet at Ocean Beach; 5 feet in Alameda; and 4 feet at Alcatraz Island, Treasure Island, Aquatic Park, Redwood City and Richmond. Cascadia scenario: Given its proximity to the Cascadia subduction zone, Del Norte County — the state's northernmost coastal region — is perhaps more exposed to tsunami risk than any other part of California. If people wait 10 minutes after an earthquake to evacuate — the shaking itself would be the warning to flee — more than 3,150 are at risk of being killed or injured by tsunami in Del Norte County, and more than 720 would be at risk in neighboring Humboldt County. Flooding could reach up to 30 feet above the average high tide along the outer coast of Humboldt Bay and the Eureka area, and up to 50 feet toward Crescent City. 'A large quake generated by the Cascadia subduction zone could create waves twice as large as the 1964 event, especially in Crescent City,' Rick Wilson, a former head of the California Geological Survey tsunami program, said in a statement. Damage estimates: Del Norte County, which is home to Crescent City, could see more than $1 billion in damage. Humboldt County, home to Eureka, could see $22 million.
