Earthquake Modeling

The ground beneath us is always moving—but what can it reveal about our future? From detecting nuclear tests halfway across the globe to simulating the devastating effects of earthquakes before they strike, this episode explores how LLNL’s work is making the world a safer place—one seismic wave at a time.

• 0:01Speaker 00

  You're out for a walk on a beautiful afternoon. The late-day sun warming your skin, fall leaves crunching underfoot, cloudless blue skies. Your phone buzzes in your pocket. You pull it out to see an alert flashing across the screen. Earthquake, early warning, strong shaking expected in 10 seconds. You freeze for a moment, heart pounding as your mind races. Is this really happening? You glance around. A flock of birds suddenly lifts from the trees. Then, the ground starts to shake. At first, it feels faint, but the shaking grows stronger.

• 0:41Speaker 00

  You steady yourself, gripping a nearby tree, and take deep breaths as the tremors intensify. Now imagine you're a scientist. You're sitting in a seismic lab where vibrations from across the globe are recorded and analyzed in real time. Are these rumbles natural tectonic movements deep beneath the Earth? Has there been a large industrial accident? An underground nuclear test in a foreign nation? Or could there be another cause entirely? Today, we're diving into the world of seismic monitoring, where scientists at Lawrence Livermore National Laboratory use cutting-edge technology to answer these very questions.

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  We'll explore how they determine whether a rumble is an earthquake, an accident, or something more ominous. Welcome to the Big Ideas Lab, your weekly exploration inside Lawrence Livermore National Laboratory. Hear untold stories, meet boundary-pushing pioneers, and get unparalleled access inside the gates. From national security challenges to computing revolutions, discover the innovations that are shaping tomorrow, today.

• 2:09Speaker 01

  I do a mixture of management and science. I lead a group of about 40 scientists that work on nuclear explosion monitoring, research and development. And then I do a little bit of active research myself still, which is great.

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  Bill Walter leads a team of scientists at Lawrence Livermore National Laboratory, dedicated to seismic and nuclear test monitoring. Work that plays a key role in tracking nuclear explosions globally and understanding seismic activity. Scientists at the lab are constantly monitoring both seismic events like earthquakes and human-created explosions. Seismic monitoring became critical in the 1960s during the Cold War, when nuclear tests were forced underground. The Limited Test Ban Treaty banned nuclear tests in the atmosphere, outer space, and underwater. This shift meant that detecting underground nuclear detonations became vital for global

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  security, and seismic analysis quickly emerged as the primary tool.

• 3:07Speaker 01

  If an explosion goes off in the ground, it generates seismic waves, just like an earthquake does. And in fact, the waves look a lot like an earthquake. And so the big challenge is, when we detect seismic waves, what's the source? What's the cause of them? Is it an earthquake? Is it an explosion? Is it a mine blast? Is it some kind of an accident? There's many things that can generate seismic waves.

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  Long before seismic waves became a key tool for detecting underground nuclear tests, nuclear explosions were happening out in the open.

• 3:39Speaker 00

  By the 1950s and 60s, nuclear tests were a regular occurrence. Above ground, underground, and even underwater. Massive mushroom clouds became symbolic of that era. But unchecked testing posed serious risks to the environment, to people, and to global security. This led to treaties like the Partial Test Ban Treaty in 1963, and later the Comprehensive Nuclear Test Ban Treaty in 1996, which aimed to stop nuclear testing altogether. Bill's work is part of an ongoing legacy that began during this time of scientific and diplomatic cooperation between the US and the Soviet Union. The challenges remain significant, with seismic monitoring at the forefront of keeping

• 4:24Speaker 00

  the world safe from hidden nuclear detonations.

• 4:28Speaker 02

  In October 2006 Pyongyang announced its first nuclear detonation.

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  North Korea's state television gave details of its explosive power.

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  It took place underground in tunnels dug into mountains in the northeast.

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  The underground explosion occurred just before 2 o'clock in the morning. It measured 4.7 on the Richter scale according to America's National.

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  Nuclear tests are still happening today. Countries like North Korea have continued to develop and test nuclear weapons, often in defiance of international law. But how do we detect these tests? The answer lies underground.

• 5:06Speaker 01

  I remember very distinctly I was taking my youngest daughter to college in September 2017 and I had helped her move in and I was back in my hotel room and I was checking my email and there's a note. I had one of these emails, which doesn't happen very often, and immediately looked at it compared to past North Korean tests and saw that this is probably a North Korean nuclear test. And there was immediately a flurry of tweets going on about people saying this looks like a North Korean test and people were immediately trying to do analysis. So there's a very active international community that follows this stuff and it's activated in minutes.

• 5:45Speaker 00

  When seismic waves are generated, they travel through the earth, bouncing off different layers of rock, soil, and water. These waves are picked up by sensors all over the world, forming the foundation of global nuclear test monitoring systems. But how do you tell the difference between an earthquake and a nuclear test, especially when they can look so similar on a seismogram? To answer that, let's look at how seismic waves work. Imagine you drop a stone into a pond. The ripples travel outward and if you watch closely, you can see that the size, shape, and speed of those ripples tell you something about the stone. Seismic waves work the same way.

• 6:28Speaker 00

  When an earthquake or explosion happens, the energy sends out waves in all directions rippling through the earth.

• 6:35Speaker 04

  Seismic means an event that generates waves that propagate through the Earth, and those are seismic waves. They are important because those are the signals that tell us where the source was located, what was the origin, what was its content, what was the magnitude of that event. So all these are characteristic of a seismic event.

• 7:01Speaker 00

  Arbin Patarka leads a group at Lawrence Livermore National Laboratory that focuses on creating detailed computer models of how seismic waves travel through different materials. These models are crucial because the Earth's surface isn't uniform. It's made up of mountains, valleys, dense rock, and soft sediment, all of which affect how seismic waves move. Arbin's team uses advanced computational methods and high-performance computers to simulate how seismic waves behave. This helps scientists better understand the differences between natural earthquakes and other seismic events, like nuclear tests.

• 7:39Speaker 04

  In order to simulate ground motion, you need to have a seismic model of the Earth, and machine learning can help a lot. We're using so-called multi-resolution models that can be produced using machine learning.

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  One example of how seismic monitoring works in action is North Korea. Their first test in 2006 sent seismic waves across the globe.

• 8:03Speaker 05

  North Korea should not test this nuclear device. If they do test it, it will be a very different world the day after the test. All we can tell from our records is that this is a seismic event.

• 8:18Speaker 06

  The U.S. Geological Service's detection of a 4.3 magnitude tremor at the Pronggadi nuclear test site signaled North Korea's arrival as the world's eighth nuclear power. On October the 9th, 2006, the DPRK announced it had successfully

• 8:32Speaker 00

  conducted an underground nuclear test.

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  Over the years, North Korea has conducted six nuclear tests, all underground. Each time, the global network of seismic sensors detected the explosions within minutes, despite North Korea's secrecy.

• 8:51Speaker 01

  North Korea has tested six times they've declared nuclear tests. Each time they tested it, the first time you could look at the waveforms and compare them to the previous ones, and you could tell very quickly that this is another test from North Korea.

• 9:04Speaker 00

  Imagine that. A test conducted in a remote area of North Korea detected halfway across the world and identified as a nuclear test within minutes. This kind of rapid detection is critical for national security and global diplomacy. It allows governments to respond quickly, gather intelligence, and assess the situation.

• 9:25Speaker 01

  It's important for countries to understand what each other are doing. If we want to have stability in the world and peace in the world, we want to make sure that no one is off developing some sort of weapon system that nobody knows about. So being able to have a clear understanding of what's happening in the world is very important.

• 9:43Speaker 00

  Fortunately, full-scale nuclear tests, like what we have seen in recent years with North Korea, are few and far between. But other kinds of events are more common. For example, chemical explosions.

• 9:56Speaker 01

  It's a pretty big difference. So a chemical explosion is like dynamite. It's a chemical reaction that generates a lot of gas usually in a rapid fashion. And if you contain that underground, it will create seismic waves. But the energy is coming from that chemical energy. So it's what scientists would call a lower-density energy. Nuclear, there's a chain reaction of fission with atom splitting. And so you have a lot of energy being generated from radiation. You have a much higher energy density, a lot of energy in a much smaller space, much more quickly.

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  Seismic monitoring isn't just for detecting explosions. The same tools are also applied to studying natural disasters.

• 10:41Speaker 01

  It's not like we're sitting around waiting for an explosion to happen. One of the interesting things that happened recently, the Hanga Tonga volcanic eruption out in the Pacific.

• 10:52Speaker 01

  That was an enormous explosion. It was a case where an island was blown up in something that was equivalent to a megaton-sized explosion. Several of them, actually. It was formed by the lava coming up and interacting with the seawater, causing explosive eruptions. That created seismic and acoustic waves that were detected by the CCBT International Monitoring System and a whole group of people analyzed that. And there's been a whole bunch of papers that have come out of that.

• 11:22Speaker 06

  We are experiencing quite a bit of shaking. If you'll give us a brief moment here, we're making sure that nothing...

• 11:28Speaker 02

  Tonight, the aftermath and aftershocks in California from the largest earthquake in three decades. The massive 7.0 magnitude earthquake striking the northern coast, prompting a tsunami warning for more than 5 million people.

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  The Earth is constantly in motion, sending seismic waves of energy through its crust. Motion that, when unleashed, can change everything.

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  Turkey and northern Syria are vulnerable to earthquakes. They sit at the junction of four tectonic plates with fault lines along their margins.

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  In 2023, a 7.8 earthquake in Turkey and Syria leveled thousands of buildings and killed over 21,000 people.

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  In geological terms, it's one of Turkey's worst. But crude measures of geological force don't tell us much about the human scale of this tragedy. 7.5 magnitude quake struck close to the fishing region of Dongala. More than 300,000 people lived there.

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  In 2018, a 7.5 magnitude earthquake triggered a tsunami in Indonesia.

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  The tsunami that followed the quake brought waves as high as six meters.

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  Destroying towns and villages.

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  Coming in and simply wiping away the buildings on the shore.

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  And killing over 4,300 people.

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  Devastating scenes that we are finding out of Nepal, where a 7.8 magnitude earthquake struck near the capital city of Kathmandu.

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  And in 2015, Nepal faced a catastrophic 7.8 magnitude quake that left more than 8,800 people dead.

• 13:05Speaker 00

  Early detection and preparation are critical. Scientists at Lawrence Livermore National Laboratory are continually advancing seismic monitoring techniques to help predict and mitigate the impact of future seismic events. Their research is key to enhancing global safety and resilience against nature's deadliest forces.

• 13:27Speaker 01

  There's a saying in the business that earthquakes don't cause destruction, it's the engineering that really causes the problems. If you can engineer your building to withstand the shaking, then it's going to survive and do very well in earthquakes. But understanding how big that shaking is going to be and what its frequency content might be is important.

• 13:46Speaker 00

  A component of this work is advanced simulations that model how seismic waves interact with diverse geological structures. Arben and his team at the lab use these simulations to deepen our understanding of seismic activity and refine earthquake hazard assessments. Earthquake modeling involves simulating the seismic behavior of the Earth's crust to understand and predict when earthquakes can happen and their impact.

• 14:13Speaker 04

  Modeling started a long time ago, and it's a tool that is needed to actually not only explain recorded data, so we have seismic events that are recorded somewhere, and in order to understand their characteristic, you can use modeling to understand the main feature and where they come from. A seismic signal is affected not only by the source where it came from, but also through the wave propagation, wave path. The modeling is important because not only you can understand what was recorded, but you can also predict what could be the characteristic of a ground motion in the case of a seismic event.

• 14:56Speaker 00

  This kind of research is paying off. In places like San Francisco, where the risk of a major earthquake looms large, scientists are using seismic data to help create buildings that can better withstand the tremors. And while the science is complex, the goal is simple: to keep people safe.

• 15:17Speaker 04

  The large-scale simulations are something that a lot of engineers are more and more interested right now because we don't have enough data for large earthquakes and we cannot wait or afford waiting for a big one to really understand what can happen and what is the expected damage. So we are starting right now with this new technology to work with engineers and it has been very productive.

• 15:45Speaker 00

  California, with its crisscrossing fault lines, has long been on high alert for the next big one. The U.S. Geological Survey predicts a 72% chance of a major earthquake, 6.7 or greater, hitting the Bay Area within the next 30 years. And Lawrence Livermore National Laboratory, located right in this vulnerable region, is leading the charge to prepare for it.

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  The Earth is a constantly changing environment. Waves can bounce off different materials, get distorted, and even overlap with other seismic events like aftershocks.

• 16:25Speaker 01

  The Earth is a really complicated filter. The Earth can change an explosion signal and make it look just like an earthquake and it can take an earthquake signal and make it look like an explosion. That's our biggest challenge.

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  Seismic waves don't move instantly. They travel through the Earth at different speeds, depending on the distance and the material they pass through.

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  It can take up to 13 minutes for the waves to travel from one side of the Earth to the other side of the Earth.

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  One of the ways scientists are refining their models is through controlled experiments. Lawrence Livermore runs a series of experiments called source physics experiments. These experiments involve setting off large chemical explosions in different types of geological formations, like dense rock or soft sediment, and studying how the seismic waves behave. In 2023, for example, they detonated a 16-ton chemical explosion in Nevada.

• 17:20Speaker 01

  It ended up being a team of over 100 people from four labs, working for months and months to prepare for this experiment. The scale of that is really quite amazing.

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  Scientists monitored the explosion using a network of sensors, and the data they gathered helped improve their understanding of how waves travel through different types of rock.

• 17:41Speaker 01

  The fact that we can think of, "Well, what do we need to do?" and come up with an idea that gets discussed among a team of people, and then a plan developed, and then put in motion to execute it is really quite incredible to see that happen. It's not something that I have experienced anywhere else.

• 17:57Speaker 00

  The first test in this series involved a "tamped" explosion, meaning it was fully contained in the ground. But future tests will explore explosions in more unusual environments, like an empty cavity. For years, there has been concern that countries might use underground cavities to hide nuclear tests.

• 18:18Speaker 01

  You can reduce the size of the seismic waves by approximately a factor of 70 if you do something in a cavity. And we're looking at ways to tell if somebody is doing that. We're looking for signatures that somebody is testing something in a cavity, trying to hide a nuclear test. So it's a really important thing to be able to develop some techniques to identify that and use it to better understand what's happening out there in the world.

• 18:42Speaker 00

  Seismic research does more than uncover hidden tests. It deciphers the unseen movements of our world, building trust and accountability on a global scale. As technologies advance, so must our efforts to outpace those who seek to obscure their activities, ensuring that our commitment to a safer, more transparent future remains unshaken.

• 19:07Speaker 00

  From the quiet crunch of leaves on a fall day to the immense power of a nuclear test or a devastating earthquake, seismic waves carry stories that shape our world. At Lawrence Livermore National Laboratory, these stories aren't just recorded. They're decoded, understood, analyzed, and transformed into actionable insights that protect lives, strengthen security, and prepare us for what's to come. The ground beneath us may shift, but thanks to this groundbreaking work, we stand on firmer footing. Because whether it's the subtle vibrations of daily life or the thunderous rumble of a major event, every tremor teaches us something and ensures that we're ready for the next one.

• 20:08Speaker 00

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