Examples of the Uses of Comprehensive Nuclear-Test-Ban Treaty Verification Data for Advancing Earth Sciences

The seismic component of the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) consists of 170 seismic stations in 76 countries around the world.  The purpose of these stations is to detect nuclear explosions, and if they occur, determine the location, timing, and yield of the detonation.  This goal is achieved by analyzing seismic waves generated by explosions that travel through the Earth, hence these waves carry information not only about the explosion, but also about the Earth's internal structure.  Even though investigation of the Earth’s subsurface is not a goal of the CTBTO’s seismic network, the stations serve unexpectedly well as powerful telescopes to view inside the Earth.

The seismic data show us the Earth’s interior from just beneath our feet to all the way down to the centre of the planet, at almost 4,000 miles below the surface.  Detailed knowledge of the internal structure is essential to unravel the dynamics and history of the Earth.  For example, just as there are continents and oceans, there are regions of fast and slow seismic wave speeds within the Earth's mantle.  Such structure is thought to be related to mantle convection which drives plate tectonics and hence processes at the surface (e.g., where earthquakes occur).  Diving even deeper, the Earth’s iron core, which is more than 2,000 miles deep, is divided into a liquid outer core and a solid inner core.  CTBTO data, for example, can inform us about the properties of the transition from the outer to the inner core.  This boundary is closely connected to the operation of the geodynamo that generates the Earth's magnetic field which, in turn, shields us from harmful cosmic rays.

The scientific value of the seismic probe into the Earth's interior is enormous, but a better understanding of the underground structure ultimately improves the identification and characterization of nuclear explosions.  This is because the distortion in the seismic waves caused by the underground structure can be properly accounted for, rather than being accepted as uncertainties in nuclear explosion detection.  In addition, CTBTO data can be used to study natural phenomena such as earthquakes and ocean waves.  In particular, the real-time collection of data from stations around the world ensures that these data are included in routine global earthquake detections.  Organizations such as the National Earthquake Information Center (part of the U.S. Geological Survey) rely on these near real-time data to identify potentially disastrous giant earthquakes.