The Day the Ground Broke the Sound Barrier

Ola: Welcome back to Fault Lines. Amara: Okay, so we've got real footage this week, not a simulation. A security camera in central Myanmar catching the ground actually move. Ola: March 28th, 2025. The road just snaps sideways, two and a half meters of slip- Amara: Wow Ola: ... in about two seconds. Amara: I've watched that clip more times than I'd like to admit. Ola: And here's the awkward part. 11 episodes, asteroids, mass extinctions, oceans that stopped breathing. Amara: And never once an actual fault. Ola: A show called Fault Lines never covered a fault. Amara: Mildly embarrassing for us, honestly. Ola: So today we fix it. We're starting in Myanmar, where the rupture on the Sagaing fault apparently outran its own shear waves. Amara: A seismic sonic boom. Ola: Mm-hmm. Amara: And the paper draws a comparison to 1906 San Francisco. Ola: Wait, that 1906? Amara: That 1906. We'll get into why. Ola: And then we jump to California, a new stress study on the Mojave section, and something researchers are calling the earthquake gate at Cajon Pass. Amara: Is that a real predictive tool or a tidy story built after the fact? Ola: I've got thoughts. Amara's got different ones. Amara: Always. Ola: And by the end, we're putting the whole idea of predictable faults on trial. Myanmar's rupture path against California's paper trail. Amara: Let's start where the ground actually moved. Ola: Myanmar, go. Amara: Okay, picture this. March 28th, 2025, 12:50 in the afternoon, central Myanmar, and there's a security camera just sitting there filming a parking lot. Ola: Nothing dramatic yet. Amara: Nothing dramatic yet. And then the ground just rips sideways- Ola: Wow Amara: ... like someone yanked a tablecloth out from under a parking lot. Ola: That's one way to describe roughly two and a half meters of slip in about two seconds. Amara: Two seconds. And it's the first time anyone's caught a strike slip fault moving like that on video in real time. Ola: Heh. Which is, I'll admit, a little embarrassing for us. Amara: Here it comes. Ola: Eleven episodes in. We've done asteroids. We've done oceans that stopped breathing. We spent an hour on snowball Earth. Amara: And zero on an actual fault. Ola: The show is called Fault Lines. Amara: Noticed that too. Ola: Heh. So overdue. Amara: Massively. And this one earned the wait. Magnitude 7.7 near Myanmar. Ola: What's the toll? Amara: Phys.org's coverage of the new science paper out of USC puts it above 3,600 dead. Damage as high as 14% of Myanmar's economy. Ola: 14% from one rupture. Amara: One rupture, one camera, one very unlucky Tuesday. Ola: And unlike the eras we usually cover, this one runs on a clock we can actually live inside. Decades to centuries, not eons. Amara: Some of the newer literature says that clock is running faster than the models assumed. Ola: Hmm. I keep circling back to something. We've spent this whole podcast on processes running on hundred million year clocks. Amara: Right. Geologic time. Slow. Ola: This one ran on a two-second clock. So what actually happens physically when a geologist says a fault ruptured? Is it one clean snap or- Amara: Or something messier. Ola: Exactly. Two and a half meters in two seconds isn't a shrug. That's rock outrunning something. Amara: And that something is the speed sound travels through solid rock. Ola: You're telling me this thing moved faster than its own shear waves? Amara: You're gonna wanna sit down for this one. Ola: Okay. Amara? Amara: I'm not saying anything yet. I'm saying the rupture speed numbers are the part that made seismologists sit up straight. Ola: Okay. How fast are we actually talking? So the camera catches one snap, but the science paper says the Fault didn't stop there. Amara: No, it kept tearing 475 to 530 kilometers, according to the paper in Science. Ola: Wait, a magnitude 7.7 isn't supposed to rupture that far. What does standard scaling predict? Amara: Something like 200, maybe 220 kilometers tops. This ran more than double that. Ola: So either the Fault broke the rules or the rules are wrong. Amara: Bit of both. And the speed makes it worse. Rupture velocity exceeded five kilometers a second. Ola: Compared to normal? Amara: Normal strike slip ruptures move two to three kilometers a second, right around shear wave speed. This one outran its own shear waves. Ola: How do you outrun a wave you're generating? Amara: That's super shear. UCLA's Lingsen Meng calls it breaking the sound barrier, except in rock. Ola: A sonic boom underground. Amara: Basically, and they caught the actual shock front, a Rayleigh Mach wave that passed through parts of Thailand hundreds of kilometers out. Ola: They detected the boom itself? Amara: The wave itself. Meng's point is that shock front can roughly double shaking intensity way out there. Ola: Okay, but why this fault? Smooth, straight faults are supposed to be the boring, well-behaved ones. Amara: So smooth doesn't mean gentle. It means unobstructed. Right. Stack that with stress banked since the last major rupture back in 1839, plus contrasting rock stiffness across the fault interface, and you've built a runway. Speaker 3: Three things stacking, not one. Amara: Geometry, banked stress, material contrast. UCLA's release spells out all three. Speaker 3: If a structurally simple fault does this, what happens to every hazard map that assumes simple equals predictable? Amara: That's the uncomfortable part. The science authors point straight at 1906 San Francisco as the closest analog. Speaker 3: Shut up. 1906 ran SuperShare too? Amara: They call Mandalay a modern stand-in for it, and the paper flags that probabilistic hazard models don't really account for long ruptures at moderate magnitude. Speaker 3: Because they assume length and magnitude move together. Amara: Which clearly isn't a rule here. Speaker 3: So 1906 is the ghost in the room, and there's a California fault that hasn't let go since 1857? Amara: Fort Tejon. Yeah. That's exactly where the numbers start looking uncomfortable. Speaker 3: Then that's probably where we go. Ola, the Sagaing rupture blew through a seismic gap. Now flip that on its head. California's got a spot where the gap might actually hold. Amara: Cajon Pass. Speaker 3: Right. There's a new paper in JGR Solid Earth, June 3rd, from Liliane Burkhard's team. They ran a thousand years of stress simulation across the San Andreas and San Jacinto systems. Amara: A thousand years on a computer? Speaker 3: Modeled, yeah, anchored to a thirty-one site paleo seismic record and real GNSS slip rate data. Educated modeling, not just guesswork. Amara: I'll take it. Speaker 3: They're tracking stress in megapascals, MPa. Think of it as pressure building in a closed pipe. Amara: Right. Speaker 3: North of Cajon Pass, that pressure climbs about one point eight megapascals every century. South of it, only one point zero to one point five. Amara: Uneven pressure on either side of the same gate. Speaker 3: Exactly the setup. By 2025, the model puts the Mojave South segment at roughly two point eight megapascals, the highest in the entire thousand-year record- Amara: Wow Speaker 3: ... according to the ScienceDaily coverage. Amara: And nothing's let that out since? Speaker 3: 1957, the Fort Tejon earthquake, magnitude seven point nine. Nothing near that scale close to LA since. Amara: Almost a hundred and seventy years of banked stress. Speaker 3: Which is the whole idea behind the gate. CNN called it the earthquake gate for a reason. Ruptures historically stall at that junction when the stress on either side is mismatched. Amara: But pass through when it's balanced. Speaker 3: Right. And Burkhard reads it per that CNN piece as today's numbers drifting toward the pass-through case. Amara: Okay. Here's where I wanna connect it. The Sagaing fault banked something similar. Its last major rupture near the segment was back in 1839. Speaker 3: Almost two centuries. Amara: And the Cajon quake tore straight through ground that had been quiet that whole time. So quiet never really meant safe, just loaded. Speaker 3: My problem is a model's only as good as what you feed it. Amara: Mm-hmm. Speaker 3: This is a stress bookkeeping exercise. It tells you where pressure sits, not when the valve blows. Amara: Sure. But bookkeeping that's tracking real slip rates and real paleo seismic dates isn't nothing. Speaker 3: I'm saying two point eight megapascals is a number to work about, not a countdown clock. Amara: Fair. Southern California Edison's 2026 planning report isn't treating it as trivial either. They've flagged transmission lines crossing the San Andreas right at that pass. Speaker 3: Yes, but a joint rupture through Cajon Pass could run seven point four to seven point eight. That's highways, rail, and power lines in the same afternoon. Amara: Across several cities at once. Speaker 3: So the model says the gate's edging open. The real test is whether stress history predicts rupture behavior or just explains it afterwards. Amara: Which is exactly what Myanmar put on trial. That rupture didn't even start where the gap was supposed to hold it. Speaker 3: Funny how the fault that blew through its own gap is the best argument for worrying about ours. Building on that stress math, here's a wrinkle. The Sagaing rupture didn't even start inside the seismic gap USC flagged as the danger zone. It kicked off outside it, ran straight through it, then kept going another two hundred kilometers past the far edge. Amara: Phys.org's coverage of the science paper has the USC team reading that as proof gaps mark where stress sits, not where a rupture starts or stops. Speaker 3: Which is exactly my problem with Cajon Pass. If a gap mapped couldn't even hold the Sagaing rupture, why should I trust a mapped junction to stop one? Amara: Because it's a different claim. Sylvain Barbot on that same study pointed out a structurally simple fault still threw a multi-segment quake. The lesson isn't that the maps are wrong. It's that smooth geometry doesn't buy you predictability. Speaker 3: Okay. But Temblors review of Cajon Pass paper accepted the simplifying assumptions and still said flatly it doesn't narrow the one thing that matters, when the next rupture actually begins. Amara: Wait. They said that outright? Speaker 3: Yeah. And they flagged something else. Amara: Right. Speaker 3: The San Jacinto Fault racks up way more small quakes than the San Andreas sitting right next to it. Nobody's pinned down why. Amara: So what's your alternative? Hand hazard planners nothing? Ola: No. I want an observation that could actually break the gate idea. Show me a rupture starting inside a quiet junction and blowing straight through it. Amara: So is that fault memory a real physical property or bookkeeping that just looks smart after the fact? Ola: Ask me after the next one ruptures where the model says it can't. Amara: Mm-hmm. Ola: Until then, I call it good bookkeeping. Amara: Fair. Those MPa numbers are still the closest thing to a falsifiable claim we've got. Ola: Falsifiable eventually. Useful for headlines today. That's the honest split. Amara: Speaking of overlooked stress, wait until you hear what's sitting right under Seattle. Ola: Building on that uncertainty, Seattle's got its own surprise, and it's not the fault everyone watches. Amara: Right. Everyone points offshore at Cascadia, but ScienceDaily just covered a GSA bulletin study on the faults running directly under the city. Ola: Under Bainbridge Island too, apparently. Amara: Yeah. Dr. Stephen Angster and his team found these small bending faults inside the Seattle fault zone rupture roughly three hundred and fifty years. Ola: Wait, that's way more often than the main fault. Amara: Way more, and they've dominated the surface ruptures there for about twenty-five hundred years. The big one everyone worries about barely shows up. Ola: So the main fault is the celebrity and the actual troublemaker some side street nobody mapped. Amara: Pretty much. It's absorbing something like fifteen percent of the total strain moving through the Pacific Northwest. Ola: And you can't just walk out and see these things. Amara: No. Most strands never break the surface. They found them with magnetic surveys, lidar, the slow stuff. Ola: Okay, so line up all three papers for me. Myanmar says- Amara: Ruptures can blow past what the models allow Ola: ... Cajon Pass says the junctions themselves might be sitting there loaded, primed. Amara: And now Seattle says the fault that ruptures isn't even the one on the hazard map. Ola: Three different fault systems, three different flavors of- So the show is called Fault Lines, and we finally covered one. Amara: Eleven episodes in. About time. Ola: That security footage from Mandalay stuck with me, watching the ground actually rip sideways in real time. Amara: Yeah, and then we spent an hour arguing whether Cajon Pass is a warning system or just a great story told after the fact. Ola: Which is really the takeaway, right? Stress numbers don't predict timing. They just tell you where to watch. Amara: Exactly. Physics gives you the where. Nobody's cracked the when. Ola: If this one cracked something open for you, subscribe, leave a review. Amara: Got a fault zone or a theory you think we butchered? Email us, hello@heymato.com. Ola: I read every one. Amara: Even the ones telling Ola he's wrong about super shear. Ola: Especially those. Amara: Thanks for sticking with us through this one. Ola: Next time, we go somewhere new. Until then- Amara: Take care of yourselves.