ALTHOUGH most often associated with detecting earthquakes, seismic technology is also the primary method to detect and locate underground nuclear explosions. Lawrence Livermore’s seismic research program began in the 1960s, when our weapons program needed a method to promptly determine the yield of underground nuclear explosive tests conducted at the Nevada Test Site. In response, the Laboratory’s first group of earth scientists set up four seismic stations to form a network around the test site that provided data immediately after a detonation.
Seismic research efforts received a boost from Project Plowshare, created in 1957 by the U.S. Atomic Energy Commission to explore the use of nuclear explosives for peaceful purposes. Some of the Plowshare tests were conducted to determine the characteristics of the resulting underground seismic signals, thereby enhancing our knowledge of how seismic waves travel through different geologic strata.
In 1963 the Limited Test Ban Treaty banned nuclear explosions in the atmosphere, outer space, and underwater. With nuclear explosions confined to below ground, Livermore seismologists faced significant challenges in distinguishing nuclear explosions from earthquakes and mining explosions. The ability to do so is important for monitoring underground nuclear explosions worldwide.
Within a few years seismologists provided an important new technology: digital seismographs running continuously at the test site and acquiring data from infrequent nuclear explosions, as well as from earthquakes large and small. In the early 1980s, the Department of Energy deployed the Regional Seismic Test Network, composed of five continuously recording seismic stations around the United States and Canada. Livermore scientists helped to analyze the reams of data these sensitive stations captured.
By the early 1990s, the fall of the Soviet Union and the end of the Cold War gave renewed impetus for a Comprehensive Nuclear-Test-Ban Treaty (CTBT). The U.S. ceased nuclear explosive testing in 1992, and the CTBT was signed by President Clinton and other heads of state and government in 1996.
The Laboratory has played a significant role in supporting the CTBT’s international system of automated seismic monitoring stations. The stations transmit data via satellite to the International Data Center in Vienna, Austria, which in turn distributes the data to national data centers around the world for analysis.
Livermore supports the U.S. National Data Center (NDC) at Patrick Air Force Base in Florida, which is responsible for U.S. nuclear explosion monitoring as part of its international treaty monitoring mission. Our diplomats and scientists recognize that the value of nuclear treaties rests, in large part, on the technical capabilities available for monitoring compliance.
Several years ago, the U.S. NDC requested a technique to integrate regional-distance seismic data with its conventional long-range data. In response, Livermore seismologist Stephen Myers led a research effort that included scientists from Los Alamos and Sandia national laboratories. As Seismic Research Making Waves describes, the resulting technology—the Regional Seismic Travel Time (RSTT) model—improves the accuracy of locating seismic events by using a three-dimensional (3D) model of Earth’s crust and upper mantle to accurately incorporate regional seismic data for enhanced detection. Small-yield events are detected quickly and with an accuracy once achieved only with large, globally recorded events. The program has already been adopted by many nations. In addition, RSTT permits seismologists to better locate and characterize local earthquakes, their primary task.
Livermore seismic researchers are currently pursuing even more-accurate 3D models and developing new “big data” applications. Currently, each seismic event is analyzed on its own, independent of hundreds of previous seismic events in the same region. We are looking for ways to exploit the enormous data set we have accumulated over more than 60 years. Combined with 3D Earth models, we will then be able to create high-fidelity “synthetic” waveforms that any seismic station is likely to see. With these and other forthcoming advancements, a rogue nation or terrorist group attempting to silently set off a small clandestine nuclear explosion is likely to create a thunderous seismic disturbance that the entire world will “hear.”