Researchers Develop Better Way to Detect Nuclear Blasts

In fact, determining accurate seismic locations for detected events — such as nuclear blasts — is a highly important aspect of nuclear test monitoring because location is key to identifying such events.

However, precisely locating events — especially small events recorded by limited numbers of monitoring stations — has proven difficult. Standard models to estimate arrival times of seismic waves can be in serious error for some source and station locations. (Seismic waves travel through the Earth, often as an earthquake, but sometimes from a nuclear blast.)

In their ESTC Award-winning article, SAIC's John Murphy, Theron Bennett, and Brian Barker summarized results of a three-year study designed to improve the way researchers locate small seismic events in eastern Asia. Their work included developing a new three-dimensional (3D) velocity model to better calibrate travel times of seismic waves for monitoring stations in eastern Asia.

For the new model, the researchers assembled and archived a large database of travel-time observations from ground truth events — explosions and earthquakes. This included a unique database of more than 1,000 carefully validated regional P-wave (the fastest seismic waves) arrival time observations from Soviet peaceful nuclear explosions and weapons tests, as well as large samples of observed travel times from ground truth events from the India/Pakistan and China/Mongolia regions. (Because many of the 30 monitoring stations had not been installed, the researchers' calibration was indirect — they used data recorded at historical surrogate stations near the planned stations to assess travel-time accuracy across the region.)

According to the authors, their new 3D velocity model for eastern Asia represents a significant improvement over the standard prediction model (known as IASP91). They expect that the 3D velocity model will provide excellent seismic event location capabilities, particularly for events recorded by the sparse network of regional IMS stations in eastern Asia.

In fact, such capabilities could help establish a more robust nuclear test-monitoring, which is critical to determine if a country is attempting to test the design and development of nuclear weapons.

The article by Murphy, Bennett, and Barker (and colleagues), "Calibration of International Monitoring System (IMS) Stations in Central and Eastern Asia for Improved Seismic Event Location," was published in the Bulletin of the Seismological Society of America.