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Yahoo
20 hours ago
- Science
- Yahoo
The San Andreas Fault: Facts about the crack in California's crust that could unleash the 'Big One'
When you buy through links on our articles, Future and its syndication partners may earn a commission. Quick facts about the San Andreas Fault How long is the San Andreas Fault? About 746 miles (1,200 kilometers) What was the biggest earthquake on the San Andreas Fault? The Great San Francisco Earthquake of 1906, which had a magnitude of around 7.9 When was the San Andreas Fault discovered? 1895 The San Andreas Fault is California's longest and most famous fault. At this fracture zone, two plates of Earth's crust move past each other. It stretches from the Salton Sea in Southern California to off the coast of Mendocino in Northern California. On the inland side of the fault, the North American Plate moves southeast. Toward the coast, the Pacific Plate creeps northwest. The San Andreas is capable of creating big, destructive earthquakes. Earthquakes are measured in magnitude on a scale that starts at zero. In this scale, each whole number represents an earthquake 10 times as large as the one before it. Most earthquakes under magnitude 2.5 aren't felt, while 2.5- to 5.4- magnitude quakes usually cause some shaking but not much damage. Quakes of 5.5 magnitude and higher cause damage to buildings, and earthquakes over 7.0 are considered major. In 1906, the northern section of the fault shook San Francisco and the Bay Area with a 7.9 magnitude quake, which caused a devastating fire in the city and killed more than 3,000 people, according to the U.S. Geological Survey. In 1857, the southern section of the fault shook and created a quake thought to be just as large. Only two people died, because California had a tiny population at the time. Geologists warn that the San Andreas will give off a large earthquake again — the only question is when. Over the past 3 million years, the San Andreas Fault has moved an average of 2 inches (56 mm) per year. If that rate continues, Los Angeles and San Francisco will be next-door neighbors in 15 million years! The 1857 Fort Tejon quake on the southern San Andreas Fault lasted between one and three minutes. During the 1906 Great San Francisco earthquake, 296 miles (477 km) of the fault moved. The San Andreas Fault was discovered just 11 years before the 1906 earthquake by geologist Andrew Lawson, who worked at the University of California, Berkeley. The San Andreas Fault is a "right-lateral strike-slip fault." That's a complicated way to say that if you stood on the North American Plate side of the fault facing the Pacific Ocean, the Pacific Plate side of the fault would be moving slowly to the right. At the San Andreas, the two plates are like blocks that are moving past each other and sometimes getting stuck along the way. When they get unstuck — quickly! — the result is a sudden earthquake. The fault is split into three segments. The southern segment starts northeast of San Diego at Bombay Beach, California, and continues north to Parkfield, California, near the middle of the state. A quake on this segment would threaten the highly populated city of Los Angeles. The middle section of the San Andreas is known as the "creeping section." It stretches between the California cities of Parkfield and Hollister in central California. Here, the fault "creeps," or moves slowly without causing shaking. There haven't been any large quakes on this section within recorded history, but scientists think there may have been earthquakes there at some point in the past 3 million years. Finally, the northern section of the San Andreas spans from Hollister to a special spot called the "triple junction" off the coast of Mendocino. The triple junction is where the North American tectonic plate, Pacific plate, and undersea Gorda plate meet. At this junction, the way the plates move past each other on the San Andreas Fault transforms into a different kind of geology known as a subduction zone. In the subduction zone, the Pacific Plate slides under the North American Plate instead of alongside it. The San Andreas Fault is about 746 miles (1,200 km) long and about 10 miles (16 km) deep. While the San Andreas is a giant fault that is even visible from space, if you zoom in, you'll see a network of many faults coming off the San Andreas. So the whole region is known more generally as the San Andreas Fault zone. This area includes faults like the Hayward Fault, which runs through the East Bay area. These side faults can produce their own serious earthquakes. For example, in 1868, the Hayward Fault rumbled to life with a magnitude 6.8 quake that killed 30 people. A similar quake today would affect the Bay Area, where millions of people live. A long time ago, the tectonic plate under the Pacific Ocean crashed directly into the tectonic plate carrying the continent of North America. The ocean plate dove under the continental plate, a pattern called subduction. Meanwhile, in the middle of the ocean there was a spot where molten lava, or magma, rose from inside Earth and formed brand-new crust. The place where the new crust formed wasn't very far from the subduction zone where crust got pushed back into the Earth. So about 30 million years ago, those two spots came together. The place where the new crust formed got pushed right under North America! This was a big change in how the geology worked in all of western North America. A new ocean plate was now touching North America. It was moving in a slightly different direction, so it didn't dive right under the continent. Subduction ended, and a new strike-slip fault (the San Andreas) was formed. The San Andreas Fault runs through and near many populated areas, including Los Angeles and the San Francisco Bay Area. It can produce damaging earthquakes, so scientists consider it a very dangerous fault. Geologists estimate that the southern San Andreas could produce a quake of up to magnitude 8.3. As far as they know, the fault hasn't ever produced a quake larger than the 1857 or 1906 quakes, both of which were probably around magnitude 7.9. That is plenty destructive, though. The magnitude 6.9 Loma Prieta earthquake that hit the Bay Area in 1989 killed 63 people. And remember that earthquake magnitude goes up by 10 for every whole number, so a magnitude 8.3 would be more than 25 times bigger than the Loma Prieta quake. If a magnitude 7.8 quake were to hit the southern San Andreas, geologists expect it would cause 1,800 deaths, 50,000 injuries and $200 billion in damage. Scientists can't predict when the next San Andreas earthquake — or any earthquake — will occur. But they can get an idea of the future risk by looking at how often earthquakes have occurred in the past. On the southern San Andreas, some sections seem to give off a good shake every 100 years or so, while others go as long as 300 years between major quakes. The Fort Tejon area, about 70 miles (113 km) north of Los Angeles, typically sees a large quake every 100 to 150 years. The last time it had a large earthquake was in 1857, so that area is considered overdue. The average time between earthquakes depends on the fault or section of the not always the same; they can vary by years or decades. Also, dangerous quakes can happen on side faults that scientists don't even know about. The magnitude 6.7 Northridge earthquake that struck Los Angeles in 1994 happened on a fault geologists previously didn't know existed. This fault wasn't part of the San Andreas, but it was a nearby fault affected by the San Andreas' motion. The U.S. Geological Survey, which tracks faults and measures earthquakes, has calculated that there's a 72% chance of a magnitude 6.7 earthquake in the San Francisco Bay region by 2043. And there's a 60% chance of a quake of 6.7 or larger in that time frame in the Los Angeles region. Image 1 of 5 One of the easiest places to see the San Andreas Fault is in the Coachella Valley of Southern California. The fault line is the narrow valley between the two white arrows, and the wrinkled landscape reveals how the movement of the plates creates hills and troughs. Image 2 of 5 The San Andreas Fault becomes complicated and branching in the San Gorgonio Pass north of Palm Springs, California. The white arrows in this image show one of the fault lines shaping this region. Image 3 of 5 The San Andreas Fault runs through Cajon Pass in California, which is a major artery for train and vehicle travel. Image 4 of 5 The 1989 Loma Prieta earthquake caused serious damage in the San Francisco Bay Area. This photo shows a car crushed under the third floor of an apartment building in the city's Marina district. The ground liquefied due to the shaking, causing the first two floors to sink and collapse. Image 5 of 5 The Hayward Fault, part of the San Andreas Fault system, runs directly through the University of California, Berkeley football stadium. Why can earthquakes happen far from plate boundaries? The 20 largest recorded earthquakes in history Nearly 75% of the U.S. is at risk from damaging earthquakes
Daily Mail
28-05-2025
- Climate
- Daily Mail
BREAKING NEWS California rocked by earthquake felt for 100 miles
California was hit by a 3.3 magnitude earthquake on Wednesday, along a major fault line overdue for a major one. The US Geological Survey detected the tremor at 9:31am PT outside of Borrego Springs, about 87 miles north of San Diego. California experiences around 27 to 35 earthquakes per day, but most are very small and go unnoticed. However, Wednesday's quake was felt by dozens of people who reported weak to light shaking. The seismic activity comes as scientists warned the Bay Area will soon suffer a devastating earthquake in the next few decades. Sarah Minson from the US Geological Survey (USGS) said this month that the chances of the long-feared 'Big One' striking San Francisco by 2055 have risen to a staggering 72 percent. That is because the region sits on top of the San Andreas Fault, an 800-mile-long fault which runs right through the Bay Area, which is overdue for 'The Big One' - a magnitude 7.8 earthquake or higher. While Minson believes there may be some time left for Californians, USGS disagrees and warns that the first major earthquake will come in just seven years. This is a developing story... More updates to come
Daily Mail
26-05-2025
- Science
- Daily Mail
Chances 'The Big One' devastates California by 2032 skyrocket as new earthquake swarm hits area
California 's Bay Area is now almost certain to suffer a devastating earthquake within the next few decades, with some experts warning it could come as soon as 2032. Sarah Minson from the US Geological Survey (USGS) has warned that the chances of the long-feared 'Big One' striking San Francisco by 2055 have risen to a staggering 72 percent. In fact, Minson said that 'one or more magnitude 6.7 or larger' quakes are more than likely to strike Northern California within 30 years. Scientists have warned that the San Andreas Fault, an 800-mile-long fault which runs right through the Bay Area, is overdue for 'The Big One' - a magnitude 7.8 earthquake or higher. While Minson believes there may be some time left for Californians, USGS disagrees and warns that the first major earthquake will come in just seven years. 'The threat of earthquakes extends across the entire San Francisco Bay region, and a major quake is likely before 2032,' the agency wrote in a report. The last time a quake stronger than 6.7 in magnitude struck the Bay Area was the Loma Prieta earthquake that killed 63 people and injured nearly 4,000 in 1989. The new fears that 'The Big One' is on the way come as a fresh earthquake swarm rattled California's coast Monday morning, right near the northern tip of the San Andreas Fault. USGS revealed early Monday morning that seven earthquakes struck the Pacific just off the coast of Northern California between 1:54am and 7:01am ET. Five of those quakes took place just minutes apart between 4:17am and 4:38am, with one of them registering at magnitude 4.6. The swarm took place roughly 50 miles southwest of Eureka, which sits near the northern boundary of the infamous fault line. No injuries or damage has been reported. Based on historical trends, it's estimated the San Andreas causes a major quake every 150 years or so. The last one was 167 years ago. The last 'Big One' in California was a magnitude 7.9 quake that decimated San Francisco in 1906, killing 3,000 people and leveling 80 percent of the city's buildings. Minson explained that such a massive earthquake is the rarest of the rare, making the Loma Prieta earthquake look common in comparison. 'For every magnitude 8, like the 1906 San Francisco earthquake, there are 10 Loma Prieta-sized earthquakes, and 100 Napa-sized earthquakes, and 1,000 magnitude 5 earthquakes,' the geophysicist told The Mercury News. Experts predict the next 'Big One' would cause roughly 1,800 deaths, 50,000 injuries and $200 billion in damages, according to the Great California Shakeout. Despite the growing likelihood that at least one major earthquake is just years away, Minson warned that Californians need to focus more on the threat coming from smaller quakes striking the state each year. 'Even though each of those smaller earthquakes impacts a smaller area and they are less likely to cause damage, they happen so much more frequently that overall the risk from them is higher,' Minson said. The USGS scientist compared major earthquakes to shark attacks, something so rare but so terrifying that many people overlook the more immediate danger. 'Sharks kill on average about five people a year and cows kill on average about 22 people a year,' she continued. To prepare for the inevitable 'Big One,' Minson said it's important to have a backup plan of how to get in contact with family in case normal communication and transportation goes down during the earthquake. 'You want water, food, those sorts of things. Think of your pets. You can go to for more information,' she added. Although the San Andreas is drawing most of the attention when it comes to predicting California's next big earthquake, Minson warned that a lesser known fault line could be the real trigger for disaster. 'The Hayward Fault seems to have the highest rate of earthquakes,' the USGS expert explained. The Hayward Fault runs along the foot of the East Bay hills. The last major earthquake hit on October 21, 1868, measuring a 6.8 magnitude. Historical records show that five people were killed and 30 were injured. Scientists have been monitoring the fault, finding it produces major quakes ever 140 years. Researchers at the University of California, Berkley said: 'Since it has been more than 144 years since the last major earthquake, the clock is ticking.' 'It is very likely that the Hayward fault will rupture and produce a significant earthquake within the next 30 years.'
Daily Mail
19-05-2025
- Climate
- Daily Mail
BREAKING NEWS California rocked by three violent earthquakes in a matter of minutes amid fears of the Big One
California has experienced multiple earthquakes in the last two minutes in an area being closely monitored for a major quake. The US Geological Survey (USGS) detected three tremors ranging from a 2.5 to 3.8 magnitude on Monday, staring just after 11am local (3pm ET). The seismic activity hit 21 miles north of Bakersfield, home to more than 400,000 people, and 80 miles from Los Angeles. The epicenter, in Grapevine, is a known location where the San Andreas fault passes under Interstate 5, specifically at Tejon Pass. This makes the Grapevine section of I-5 particularly vulnerable to damage from earthquakes. This is a developing story... More updates to come.
Daily Mail
19-05-2025
- Science
- Daily Mail
California fault line hit by earthquakes, sparking concerns over 'The Big One'
California experienced three earthquakes in an area being closely monitored for a major quake on Thursday and Friday. The U.S. Geological Survey (USGS) detected the seismic activity along the San Andreas Fault, which spans 800 miles from Cape Mendocino in the north to the Salton Sea in the south. Scientists warn this fault is overdue for a 'Big One' - a magnitude 7.8 earthquake or higher. The recent tremors ranged from a 2.5 to 2.9 magnitude, which experts say may cause mild injuries and damages. However, no injuries or damages have been reported as of yet. Experts are 'fairly confident that there could be a pretty large earthquake at some point in the next 30 years', Angie Lux, project scientist for Earthquake Early Warning at the Berkeley Seismology Lab, previously told Experts predict the 'Big One' would cause roughly 1,800 deaths, 50,000 injuries and $200billion in damages, according to the Great California Shakeout. Based on historical trends, it's estimated the San Andreas causes a major quake every 150 or so years, and the last one was 167 years ago. USGS detected the first quake, a 2.9 magnitude, on Thursday, northeast of San Francisco. This tremor was located on Calaveras Fault, a major branch of the San Andreas Fault system. The following earthquakes hit Friday morning, one along another branch of the major fault and another directly on it. The last major earthquakes on the San Andreas fault were in 1857 and 1906. The Fort Tejon earthquake of 1857 was a 7.9 magnitude, which caused ground fissures in the Los Angeles, Santa Ana and Santa Clara Rivers. Dr Sue Hough, a scientist in the USGS' Earthquake Hazards Program, told KTLA5 that there are conflicting studies about what signs precede a major earthquake. Some research suggested more activity happens before it hits, while others have found there is no warning, she added. Scientists are monitoring another fault line in California, the Cascadia Subduction Zone, which they believe could also produce a powerful earthquake soon. New research found that a 8.0 magnitude or higher quake along the Cascadia Subduction Zone, combined with rising sea levels, would cause coastal land to sink up to 6.5ft within 30 minutes of a major tremor. The team generated tens of thousands of earthquake models to estimate the potential range of earthquake-driven subsidence — sinking land — that can be expected from the next large Cascadia earthquake. They determined that the most severe effects would hit southern Washington, northern Oregon and northern California, densely populated areas in the region. This event would result in significant expansion of the coastal floodplain — an area with a one percent chance of flooding each year — increasing it from 35 square miles to 116. If such a quake struck today, the researchers estimate that an additional 14,350 residents, 22,500 structures and 777 miles of roadway would fall within the post-earthquake floodplain, more than doubling flood exposure. The Cascadia Subduction Zone has historically produced 8.0 or larger magnitude earthquakes every 400 to 600 years, with the last striking in 1700. This might suggest the 'sleeping giant' is poised for another big one soon.
