3-D Earth model more accurately pinpoints explosions

Oct 28, 2013
A one-dimensional velocity profile with depth plotted within a three-dimensional Earth. The colors are compressional wave velocity in km/s. The rays are examples coming from a pseudo station at the North Pole. This model is used as the starting point to calculate the full SALSA3D velocity model.

During the Cold War, U.S. and international monitoring agencies could detect nuclear tests and measure their size. Today, they seek to pinpoint much smaller explosives tests. Under the sponsorship of the National Nuclear Security Administration's Office of Defense Nuclear Nonproliferation R&D, Los Alamos and Sandia National Laboratories (SNL) have partnered to develop a 3-D model of the Earth's mantle and crust called SALSA3D (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, with more accurately locating all types of explosions.

Significance of the research

After an explosion, the energy travels through the Earth as waves that seismometers at U.S. and international ground stations associated with nuclear explosion monitoring organizations detect. Scientists use these signals to determine the location of the explosion. The scientists first predict the time taken for the waves to travel from their source through the Earth to each station. To calculate that, they must know the seismic velocity of the Earth's materials from the crust to the inner core. If the energy travels through material with low seismic velocity, it takes signals longer to travel from the explosion's source to the receiver.

In the past 100 years, seismologists have predicted the travel time of seismic energy from source to receiver using one-dimensional models. However, these models do not do well at predicting travel time to nearby events where the waves spend most of their time in the Earth's crust or the shallowest parts of the mantle, both of which contain a larger variety of materials than the lower mantle and the Earth's core. Therefore, the largest errors occur close to the surface of the Earth where the most variability in materials exists.

SALSA3D and improved predictive accuracy

SALSA3D accounts for distortions of the seismic wavefronts caused by minor differences in the properties of rock and other materials. For example, waves are distorted when they move through a subduction zone, such as the one beneath the west coast of South America where one tectonic plate under the Pacific Ocean dives underneath the Andes Mountains. In recent tests, SALSA3D predicted the source of seismic events over a geological area that was 26 percent more accurate than the traditional one-dimensional . Monitoring agencies could use SALSA3D to precompute the from each station in their network to every point on Earth.

Research achievements

LANL's role is the data accumulation from the ground-based nuclear detonation detection research database for ground-truth events (seismic events where we know the location to some specific uncertainty, called LOCDB or location database), the associated paths to various seismic stations, collaboration on the tomographic process and the validation of the 3-D model for seismic location accuracy. Los Alamos provides Sandia the data to use for the tomography model (approximately ten million ray paths from approximately 13,000 distinct seismic stations and approximately 122,000 distinct events), Sandia runs their tomography code to produce the 3-D velocity model and then LANL takes the final model and runs tests to validate how well the model performs.

Explore further: Iron in the Earth's core weakens before melting

add to favorites email to friend print save as pdf

Related Stories

Iron in the Earth's core weakens before melting

Oct 10, 2013

The iron in the Earth's inner core weakens dramatically before it melts, explaining the unusual properties that exist in the moon-sized solid centre of our planet that have, up until now, been difficult to ...

Homing in on a potential pre-quake signal

Aug 02, 2012

In a new analysis of the 2004 magnitude 6.0 Parkfield earthquake in California, David Schaff suggests some limits on how changes measured by ambient seismic noise could be used as a pre-earthquake signal.

Recommended for you

NASA's HS3 looks Hurricane Edouard in the eye

8 hours ago

NASA and NOAA scientists participating in NASA's Hurricane and Severe Storms Sentinel (HS3) mission used their expert skills, combined with a bit of serendipity on Sept. 17, 2014, to guide the remotely piloted ...

Tropical Storm Rachel dwarfed by developing system 90E

13 hours ago

Tropical Storm Rachel is spinning down west of Mexico's Baja California, and another tropical low pressure area developing off the coast of southwestern Mexico dwarfs the tropical storm. NOAA's GOES-West ...

NASA ocean data shows 'climate dance' of plankton

16 hours ago

The greens and blues of the ocean color from NASA satellite data have provided new insights into how climate and ecosystem processes affect the growth cycles of phytoplankton—microscopic aquatic plants ...

Glaciers in the grand canyon of Mars?

18 hours ago

For decades, planetary geologists have speculated that glaciers might once have crept through Valles Marineris, the 2000-mile-long chasm that constitutes the Grand Canyon of Mars. Using satellite images, ...

NASA support key to glacier mapping efforts

18 hours ago

Thanks in part to support from NASA and the National Science Foundation, scientists have produced the first-ever detailed maps of bedrock beneath glaciers in Greenland and Antarctica. This new data will help ...

User comments : 0