Project Leader:
Jiakang Xie
(xie@ldeo.columbia.edu)
EI Collaborators:
Won-Young Kim
Additional External Researchers:
Khalturin Vitaly (vkhaltur@ldeo.columbia.edu)
Locations: Asia
Description:
Our recent studies show that for underground nuclear explosions (UNE) in central Asia, the source corner frequencies (fc) of regional P and S waves are very different. This difference explains why there has been an observed, statistical trend for the Pn/Lg ratios to be dependent on frequency and explosions magnitude. To explore why there is such a difference in fc values of regional P and S waves, we propose a comprehensive study to understand different excitation processes of the regional P and S waves from UNEs. Hundreds of clustered UNEs in central Asia and Nevada between the 1970s and 1990s were recorded at common regional stations. Under a reciprocal theorem, these waveforms provide dense time-space domain sampling of the wavefields in the near source region. We propose a three-stage study of the waveforms. Firstly, we shall use the source array to conduct a frequency-slowness power spectra (FSPS) analysis to determine the plane-wave composition of regional P and S waves as they leave the sources. In each frequency band we shall estimate the powers of various wavelets, including the direct, “diving” body wavelets and the scattered/multipathed waves, such as the lower frequency Rg waves. A bi-product of this stage will consist of improved depth estimates of the UNEs in Central Asia.
In the second stage we shall examine the compatibility between the observed FSPS and each of the previously proposed physical mechanisms for regional wave excitations. The best-fit mechanism will be found for each phase, in each frequency band and test site.
In the third stage we shall replace our simplified mathematical model of explosion sources by better models corresponding to the best excitation mechanisms determined in the second stage. We shall use the improved model to estimate source spectral parameters, including seismic moment and fc. We shall develop scalings of these parameters with event magnitudes and depths and explore the dynamic relations among all these parameters and testing styles, local structures, and geological environments. Accordingly, dynamic correction procedures will be developed for transporting the P/S spectral ratio discriminant across different frequencies, magnitudes and testing conditions.
EI Unit:
Lamont-Doherty Earth Observatory (LDEO)
Cross Cutting Themes:
Hazards and Risk
Core Disciplines:
Engineering
Funding Agency:
Department of Energy (DOE)
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