So... What's Going on with the San Andreas Fault? Geologist Explains

[00:00:00]Just recently, these news articles came out stating that the San Andreas fault has reached its highest level of stress in a thousand years, raising alarm bells of a possible massive earthquake occurring on the fault system in the near future. A paper published on June 3rd, 2026 in the Journal of Geoysical Research, Solid Earth, states that the southern section of the San Andreas fault near Los Angeles and the related San Hasinto fault that runs beneath San Bernardino have reached a quote critically loaded state, threatening the lives of over 20 million people across Southern California. The authors constructed a highly detailed computer model of stress accumulation and release during past earthquakes on the San Andreas fault at Coahhone Pass. Using paleocismic data from earlier studies of the fault. By analyzing these data from soil layers and rock layers along the fault, scientists have come to an alarming conclusion. Stress along the San Andreas fault at Coahone Pass has reached a critical level. But what does all of that actually mean? I'm Solomon Feinstein, geologist and science teacher, and today we're going to break down what this new research is saying and derive some important interpretations from it so that you can be more informed, more prepared, and more safe. We'll start by discussing some brief geology of the San Andreas fault. Let's do it.

[00:01:26]The San Andreas fault is one of the most studied fault lines in the world due mainly to its close proximity to large urban areas and its excellent exposures and catalog of geological record denoting the boundary between the Pacific and North American plates. It runs for roughly 800 m from the Sultan Sea in the south to Cape Mendescino in the north. At the San Andreas fault, the Pacific and North American plates laterally slide past each other at a rate of roughly 1 to two inches per year, forming what is known in geology as a transformed plate boundary. Though the San Andreas fault is the big bad wolf of the area, it's really just the main fault line in a complex system of related faults. As the two tectonic plates slide past each other, they tend to get stuck, accumulating large amounts of stress and potential energy. An earthquake occurs when this stress reaches a critical point and the fault can't take it anymore, releasing all of the builtup energy at once as potential energy is transferred to kinetic energy.

[00:02:27]The seismic waves generated from that energy release are what cause the shaking during an earthquake. The San Andreas is split into three main sections. The northern, central, and southern sections. These three segments of the fault all behave differently due in large part to the geometry of the fault line, the angle and direction in which it runs, and the geology and composition of the rocks that the fault cuts through in each section. The northern section of the fault tends to rupture every 200 to 300 years. And the last time it ruptured was in 1906 when the great San Francisco earthquake and fire killed over 3,000 people and all but destroyed the city of San Francisco.

[00:03:07]While the northern section of the San Andreas fault itself isn't likely to produce a large earthquake in the near future, there are several related faults throughout the San Francisco Bay area that are very likely to produce highly damaging earthquakes in the near future, such as the infamous Hayward fault that runs through Oakland, Hayward, Berkeley, and other cities in the East Bay. To learn more about the Hayward fault, click on this video. The central section of the fault doesn't generally produce large damaging tremors as it tends to simply creep along without causing earthquakes undergoing a phenomenon known as a seismic creep. This occurs in the central section of the fault because of the rock that it cuts through. The central section of the fault largely cuts through a metamorphic rock known as serpentanite which is a soft platey hydrated rock. Because serpentinite contains water in its chemical formula and it's so soft, this section of the fault is basically lubricated allowing for the relatively seamless and continuous slip to occur without causing damaging earthquakes. The Calaveris fault is a fault that branches off of the central San Andreas that showcases this phenomenon beautifully in the town of Hollister about an hour south of San Jose. To learn more about the Calaveris fault, click on this video. The southern section of the San Andreas fault is the one that has geologists alarm bells ringing the loudest for a litany of reasons. This section of the fault mainly cuts through granite and nice, two very hard rocks that tend to get locked up quite easily as opposed to the softer hydrated serpentanite that the central section creeps through. As such, the rocks that this section of the fault cut through generally accumulate huge amounts of strain. Additionally, the southern section of the San Andreas fault runs through or near highly populated areas, making it all the more deadly. An estimated 20 million people live within 50 mi of the San Andreas fault in Southern California. The southern section tends to rupture every 130 to 150 years. And it has been eerily quiet since it last ruptured 180 years ago in the massive Forthon earthquake of 1857 which registered an estimated 7.9 on the moment magnitude scale. Perhaps even more alarmingly, the Coachella section of the fault tends to go every 180 years, and it last ruptured 330 years ago in 1690, making that section incredibly overdue. Since these past large earthquakes, the fault has been building up a tremendous amount of stress, reaching stress levels higher than any seen in the last thousand years. Meaning that this stress has reached or exceeded typical breaking points that triggered earthquakes along the fault within the last thousand years. An absolutely sobering reality that spells disaster for San Bernardino, Los Angeles, and other areas across Southern California.

[00:06:06]Using that beautiful thing we all love, math, scientists are able to calculate how much stress it took to caused the fault to rupture in the past. And that's exactly what the authors of this paper did. By analyzing the displacement of rocks and soil that past earthquakes caused, scientists are able to calculate their magnitudes. Because the magnitude of an earthquake is a measure of how much energy was released during it, the amount of stress accumulated along a fault line is a key component that goes into determining the magnitude of an earthquake. Basically, more stress accumulated equals more energy released and thus a more powerful higher magnitude earthquake. Using both math and computer modeling, scientists were able to derive how much stress accumulated and how much energy was released during past earthquakes along the fall. At Coahone Pass, which is located where the I-15 crosses the San Gabriel Mountains between San Bernardino and Victorville, the amount of stress that the fault has accumulated is currently 2.8 megapascals. In the past, major earthquakes occurred on this segment of the fault when stress levels were between 1.2 and 2.7 megapascals.

[00:07:16]That's pretty alarming. But wait, it just gets worse. The San Hasinto fault is a major subfault in the greater San Andreas fault system that branches off of the San Andreas at Coahone Pass and runs right through San Bernardino, Coloulton, Hamett and other areas, terminating near El Centro in the Imperial Valley. In the past, the San Hinto fault generated major earthquakes when its stress levels were between 1.2 and 2.9 megapascals. The northernmost section of the San Hinto fault is currently sitting at a stress level of 3.6 megapascals.

[00:07:52]Yeah, that's incredibly alarming. The findings of this paper suggest that a large earthquake on the southern section of the San Andreas fault in the near future is very likely, but based on what I've seen in the news, the San Hinto fault is being overlooked. It's not as famous as the San Andreas is, and it just doesn't have that household cache that the San Andreas fault does. But when you look at the facts, the San Hasinto fault is undoubtedly more dangerous to the area than the San Andreas is for one simple reason. It runs directly beneath the 4.75 million people that call the Inland Empire home.

[00:08:29]The San Andreas fault, on the other hand, skirts the San Gabriel and San Bernardino mountains at the edge of major urban development rather than right through it like the San Hinto fault. Furthermore, the San Hasinto fault has built up much more stress than the San Andreas has, suggesting that for whatever reason, it has become the focal point of tension in the southern section of the greater San Andreas fault system.

[00:08:53]According to the authors of the paper, not only are the stress levels at Coahone Pass in the northern section of the Sanhesinto fault at 1,000-year highs, they are also in the range where historically both the San Andreas and San Hinto faults have ruptured simultaneously. The study focuses on Coahone Pass specifically because it is a very important location in the southern San Andreas fault. It's where the San Hasinto fault branches off of the San Andreas fault, making it what the authors refer to as a quote earthquake gate. If there is a high amount of stress at Coahone Pass, which there most certainly is, a rupture of one fault could propagate to or cause a rupture of the other, generating an absolutely massive earthquake. This would be an unprecedented disaster for Southern California, likely generating an earthquake as strong as magnitude 7.8. The paper does not dive into likelihoods of this event occurring within a specific time frame, but other research suggests that Southern California has a 67% chance of experiencing a magnitude 6.7 or greater earthquake within the next 30 years. The same study forecasted a 37% chance of a magnitude 7.5 to strike SoCal in the same time frame. This particular study that outlines these statistics was published in 2015, meaning we are 11 years into the 30-year projection that this study made. The likelihood of a major earthquake only increases as more time elapses. If we're going off of the study, there's a 67% chance of a 6.7 plus and a 37% chance of a 7.5 plus within the next 19 years, not the next 30, as we're already 11 years into this 30-year projection. In layman's terms, we might be cooked, chat.

[00:10:43]In the event of a joint rupture between the San Andreas fault at Kahon Pass and the northern section of the San Hinto fault beneath San Bernardino, Southern California would be absolutely devastated. Back in 1812, the great San Juan Capistrano earthquake which registered a magnitude 7.5 on the moment magnitude scale began on the San Hasinto fault and propagated to the San Andreas through the so-called earthquake gate at Coahone Pass. If a similar earthquake were to occur today, which the study suggests is quite likely and may be imminent, an estimated 52,000 casualties, including over 50,000 injuries and up to 1,800 deaths, could result. Over $213 billion in property damages, would also likely occur. These figures are based off of a 2008 paper published by the USGS that outlines what they forecast would happen in the event of a magnitude 7.8 8 rupture of the southern section of the San Andreas fault. Keep in mind that this figure is based off of the San Andreas fault, which runs through the San Gabriel and San Bernardino mountains, not the San Hinto fault, which literally runs directly through downtown San Bernardino. I can't overstate that enough. The San Hinto fault literally runs beneath thousands of people's houses. A specific study outlining the possible consequences of a joint San Hasinto San Andreas fault rupture has yet to be published. But given what we just discussed, one can only surmise that this hypothetical joint rupture would be deadlier than a rupture of only the San Andreas fault. Because the I-15, the I10, the I215, and the Union Pacific Railroad crossed the San Andreas and San Hinto faults at Coahone Pass and in San Bernardino. They would literally be split in half during the earthquake, being offset by as much as 33 ft. In fact, there are literally zero roads that enter the greater Los Angeles area that don't cross the San Andreas fault.

[00:12:45]So, you do the math. With these major transportation and shipping routes being destroyed, Southern California would be marooned for up to several months. The San Hinto fault runs through neighborhoods, commercial zones, and other builtup areas in San Bernardino.

[00:13:01]We're talking about houses and other buildings on top of the Sanhinto fault, literally being ripped in half during the earthquake. Utilities like water lines, gas lines, and power lines would also be outright destroyed as the ground they're built on or in rapidly shifts beneath them. If you don't live on top of the fault line, the good news is that your house or the building you are occupying likely won't be outright destroyed. And this is because California's buildings have to be built to strict seismic code, designed specifically to not collapse in an earthquake. With that being said, dealing with months of no water, gas, or electricity will be quite the struggle.

[00:13:40]Stockpiling extra food, water, and other supplies is paramount to surviving the aftermath of a major earthquake. Now, you might be thinking, "Well, what if I don't live in Southern California? Why should I care? Surely this won't affect me." Well, let me let you in on a little secret. A major earthquake along the southern San Andreas and or San Hasinto faults would drastically disrupt the global supply chain of shipping as the largest port on the west coast is the port of Long Beach receiving and shipping over 90 million metric tons of cargo per year mainly to and from Asia.

[00:14:16]When you purchase products that are made in Asia, the vast majority of them arrive at the store you are buying them from through the port of Long Beach.

[00:14:23]They get loaded onto semi-truckss or cargo trains at the port to be sent to wherever you're purchasing them from. If all of the roads that exit Los Angeles are destroyed by an earthquake, good luck getting your products that are made in China, which by the way, most household products we still use are.

[00:14:40]I've gone into greater specifics on how a major earthquake hitting Southern California could look like in other videos, so please consider checking this video out for more specific details on that. This new study is a frightening one that highlights just how critical the tectonic situation at the southern section of the San Andreas fault is.

[00:14:59]While the research is alarming, Southern California is earthquake country and that's just a reality we need to contend with if we live in the area. While we cannot predict when exactly the next earthquake will hit, we can only be as prepared for it as possible.

[00:15:18]The purpose of this video was not to fearmonger or scare people. It was just to bring some additional context to a breaking news story in the field of science. Thanks for watching. Stay safe out there and as always, peace.

[00:15:48]Thank you for tuning in to another episode of Solomon's Outdoor Adventures.

[00:15:51]If you enjoy content like this, please like the video and subscribe to the channel and check out some of our other adventures right here. As always guys, thanks again and peace.