Big Ideas Lab: Earthquake Modeling – Summary

Episode Release Date: January 21, 2025
Host: Mission.org
Hosted by: Lawrence Livermore National Laboratory (LLNL)

Introduction to Seismic Monitoring

The episode opens with a vivid scenario illustrating the sudden onset of an earthquake, setting the stage for a deep dive into seismic monitoring. The narrative contrasts the immediate human experience of an earthquake with the scientific efforts underway to understand and predict such events.

Leadership in Seismic and Nuclear Monitoring

Bill Walter, a leader at LLNL, introduces his dual role in management and active scientific research. He oversees a team of approximately 40 scientists focused on nuclear explosion monitoring and seismic research.

Bill Walter [03:49]: "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."

His team plays a crucial role in distinguishing between natural seismic events like earthquakes and human-induced explosions, such as underground nuclear tests or industrial accidents.

Historical Context and the Evolution of Seismic Monitoring

The narrative traces the origins of seismic monitoring back to the Cold War era, highlighting the shift from atmospheric to underground nuclear testing due to treaties like the Limited Test Ban Treaty (1963) and the Comprehensive Nuclear-Test-Ban Treaty (1996). This transition made seismic analysis essential for global security, enabling the detection of clandestine nuclear detonations.

Seismic Waves: Understanding the Signals

Arbin Pitarka, another key figure at LLNL, explains the complexities of seismic wave propagation. He leads a team dedicated to creating detailed computer models to simulate how seismic waves travel through diverse geological materials.

Arbin Pitarka [08:14]: "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."

Pitarka emphasizes the role of machine learning in developing multi-resolution models to enhance the accuracy of seismic simulations.

Arbin Pitarka [09:19]: "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."

Detecting Undetected Nuclear Tests: The North Korean Case Study

The episode delves into specific instances of nuclear testing, focusing on North Korea's underground detonations. Notably, in October 2006, North Korea conducted its first underground nuclear test, registering a 4.7 magnitude on the Richter scale.

Bill Walter [06:46]: "I remember very distinctly I was taking my youngest daughter to college in September of 2017... looked at it compared to passed North Korean tests and saw that this is probably a North Korean nuclear test."

LLNL's seismic monitoring system detected six underground nuclear tests by North Korea, each identified within minutes through global sensor networks. This rapid detection is pivotal for national security and diplomatic responses.

Bill Walter [10:31]: "Tested six times they've declared nuclear tests. Each time they tested. After 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."

Natural Disasters and Seismic Research

Beyond monitoring nuclear activities, LLNL's seismic research extends to natural disasters. The team examines events like volcanic eruptions and earthquakes to enhance predictive models and mitigate impacts.

Bill Walter [12:21]: "It's not like we're sitting around waiting for an explosion to happen... the Hunga Tonga volcanic eruption out in the Pacific, that was an enormous explosion... detected by the CTBT International monitoring system."

The discussion includes devastating earthquakes in regions such as Turkey, Syria, Indonesia, and Nepal, underscoring the human toll and the importance of early detection and engineering resilience.

Bill Walter [16:31]: "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 that's going to survive and do very well in earthquakes."

Advanced Simulations and Modeling Techniques

Arbin Pitarka elaborates on the necessity of large-scale simulations to understand seismic activities, especially given the limited data from major earthquakes.

Arbin Pitarka [17:18]: "Modeling started long time ago, and it's a tool that is needed to actually not only explain recorded data... you can use modeling to understand the main feature and where they come from."

These simulations help predict ground motions and assess earthquake hazards, which are critical for designing earthquake-resistant infrastructure, particularly in high-risk areas like San Francisco and California at large.

Controlled Experiments: Enhancing Detection Capabilities

LLNL conducts source physics experiments to refine seismic models. These controlled experiments involve detonating large chemical explosions in various geological formations to study seismic wave behavior.

Bill Walter [19:53]: "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."

One notable 2023 experiment involved a 16-ton chemical explosion in Nevada, involving over 100 scientists from four laboratories. These experiments aim to identify unique seismic signatures that distinguish nuclear tests conducted in underground cavities, which could be attempts to conceal such activities.

Bill Walter [21:23]: "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."

Global Implications and Future Directions

The episode concludes by emphasizing the global importance of seismic research conducted at LLNL. Through advanced monitoring, modeling, and experimental techniques, LLNL contributes to global safety, security, and resilience against both natural and man-made seismic events.

Bill Walter [19:29]: "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 just like an explosion. That's our biggest challenge."

The ongoing collaboration with engineers and international monitoring systems ensures that LLNL remains at the forefront of seismic research, ready to respond to future challenges.

Conclusion

"Earthquake Modeling" on Big Ideas Lab provides an in-depth exploration of seismic monitoring's pivotal role in global security and disaster preparedness. Through expert insights from Bill Walter and Arbin Pitarka, the episode highlights LLNL's cutting-edge research in distinguishing seismic events, enhancing predictive models, and safeguarding communities worldwide. As seismic activities continue to pose significant threats, the advancements made by LLNL's scientists ensure a more secure and resilient future.