Detection3D Earth model accurately pinpoints source of earthquakes, explosions

During the cold war, U.S. and international monitoring agencies could spot nuclear tests and focused on measuring their sizes. Today, they are looking around the globe to pinpoint much smaller explosives tests.

Under the sponsorship of the National Nuclear Security Administration’s Office of Defense Nuclear Nonproliferation R&D, Sandia National Laboratories, and Los Alamos National Laboratory have partnered to develop a 3-D model of the Earth’s mantle and crust called SALSA3D, or Sandia-Los Alamos 3D. The purpose of this model is to assist the U.S. Air Force and the international Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) in Vienna, Austria, more accurately locate all types of explosions.

A Sandia Lab release reports that the model uses a scalable triangular tessellation and seismic tomography to map the Earth’s “compressional wave seismic velocity,” a property of the rocks and other materials inside the Earth that indicates how quickly compressional waves travel through them and is one way to accurately locate seismic events, Sandia geophysicist Sandy Ballard said. Compressional waves — measured first after seismic events — move the particles in rocks and other materials minute distances backward and forward between the location of the event and the station detecting it.

SALSA3D also reduces the uncertainty in the model’s predictions, an important feature for decision-makers who must take action when suspicious activity is detected, he added.

“When you have an earthquake or nuclear explosion, not only do you need to know where it happened, but also how well you know that. That’s a difficult problem for these big 3-D models. It’s mainly a computational problem,” Ballard said. “The math is not so tough, just getting it done is hard, and we’ve accomplished that.”

A Sandia team has been writing and refining code for the model since 2007 and is now demonstrating SALSA3D is more accurate than current models.

In recent tests, SALSA3D was able to predict the source of seismic events over a geographical area that was 26 percent smaller than the traditional one-dimensional model and 9 percent smaller than a recently developed Regional Seismic Travel Time (RSTT) model used with the one-dimensional model.