Contact: Wendee Brunish
505-667-5724

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Seismic Monitoring

Technical Objectives and Benefits

Because it will be important in Ground-Based Nuclear Explosion Monitoring (GNEM) to be able to detect low-magnitude signals from small explosions, seismic signals must be recorded at regional distances (less than 2000 km from the source). These signals propagate through the structurally complex crust and upper mantle of the earth, requiring new analysis techniques to discriminate explosions from earthquakes. Regional seismic data may be used to calibrate regions of high interest, such as China. In areas where there is little data available, regional characterization combined with earth models and synthetic seismogram calculations can assist in developing and evaluating discriminants. Study of mining practices and their effects on monitoring effectiveness can also contribute to designing an effective IMS.

Successes

We have developed and used a three-dimensional computer code for modeling seismic wave propagation in complex geologies all the way from the source to the receiver. In addition, we have implemented techniques for linking the results of strong motion calculations, which realistically capture the highly nonlinear processes involved in nuclear detonations, with the seismic wave propagation code. These techniques allow us to determine how source effects and regional propagation paths affect the relative usefulness of various discriminants in different situations. The linkage of the strong motion weapons effects codes to the regional wave propagation code can provide valuable information on the waveforms to be expected from nuclear tests in areas where such tests have not been previously conducted, or where data from known test sites is unavailable.
Chinese Seismic Sources.
The May 2, 1995, earthquake measuring 5.5 M and the May 15, 1995, explosion measuring 6.1 M exhibit markedly varying behavior along different paths.


Mining explosion or nuclear detonation? In the first 17 months of operation, an IMS prototype system, GSETT-3, detects a high percentage of mining events occuring in the Powder River Basin of Wyoming. The red vertical bars at each of the monitoring stations show the percentage of 52 events that each station recorded. Studying mining explosions and their effects on monitoring effectiveness will contribute to better designs for a future IMS.

We have also completed a study designed to quantify the differences between cylindrical and spherical explosive sources, enabling discrimination between NUDETs and mining explosions and use of cost-effective calibration explosions for validating and calibrating the international monitoring system. Results indicate that modest-cost, simultaneously detonated explosions using standard mining explosion emplacement techniques could provide regional signals for calibration purposes.

Large-scale surface cast blasting associated with open pit coal mining operations has been found to trigger stations in the prototype international monitoring system, GSETT-3. This part of the experimental program is quantifying the range of blasting activities that trigger this system as well as assessing the quality of the locations and data. Data gathered from within the mine in combination with regional signals from the same explosions have been used to develop new physical models of these types of explosive sources.


As part of our discrimination effort, we are developing distance corrections and mapping out propagation effects on regional phases such as major phase blockages. We have also been measuring and compiling travel-time tables to be used in regional location studies. Regional magnitude scales that are tied to teleseismic mb are also being developed.


Blast models.Seismic sources from all over the world will have to be identified as part of GNEM R&E. Shown here is the detonation of a large explosion in southern Russia through video images (left panels) and models (right panels). The models show the generation of compressional waves in the earth (blue rings) and the acoustic signals (yellow ring) that could serve to identify similar sources


Los Alamos Role and Deliverables

Los Alamos has four major tasks in seismic monitoring research:

Such simulations can provide a powerful means for analyzing and understanding the processes important in shaping the observed waveforms, and thereby provide a physical basis for the empirically derived discriminants. Finally, our study of mining practices, first in the United States, and eventually in China, will contribute to the understanding of how mining explosions will influence the effectiveness of the IMS.